jwn student notes

FIRESPEC ENGINEERING (M) SDN BHD

Industrial Standard and Glossary

Lighting Design

Hj Azlan Abass

11/7/2011

Proprietary and Confidential Information

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Firespec Engineering (M) Sdn Bhd By: Hj Azlan Abass

Contents

Basic Lighting Knowledge .................................................................................................. 2

1). Lumen(lm) .................................................................................................................. 2

2). Candela(cd) ................................................................................................................. 2

3). Beam Angle [Unit:degree] ........................................................................................... 2

4). LUX(lx) ........................................................................................................................ 3

5). Color Temperature / Correlated Color Temperature(CCT) ........................................ 3

6). Color Rendering Index(CR) ........................................................................................ 3

7). Efficacy(lm/W) ........................................................................................................... 4

8). Design Life Time ........................................................................................................ 4

9). Dimmability ............................................................................................................... 4

Why LED Lighting Solution ? ............................................................................................. 5

Industry Standards and Glossary ...................................................................................... 6

LumaStream embraces the industry standards evolving on both federal and state

levels. ........................................................................................................................... 6

Lumen Method Calculations ............................................................................................ 29

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Basic Lighting Knowledge

1). Lumen(lm)

Lumen is the international (SL) unit of luminous flux, a measure of overall light emitted by a light source.

2). Candela(cd)

Candela is the international(sl) unit of luminuous intensity,a measure of light emitted by a light source in a particular direction.

Any given light source will have different luminous intensities in different directions considered.

[candela = lumen/solid angle]

3). Beam Angle [Unit:degree]

Beam angle is the angle between two directions for which the luminous intensity is 50% of the

maxmum intensity as measured in a plan through the nominal beam centerline.Beam angle of a bulb

gives an idea of how the light beam spreads away from the beam center.

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4). LUX(lx)

Lux is the international(SL)unit of illuminance, a measure of light arriving at a surface, 1 lumen per

square foot equals 1 footcandle, while 1 lumen per square meter equals 1 lux .

[lux = lumen/m2]

5). Color Temperature / Correlated Color Temperature(CCT)

A black-Body radiator will have a different color whent it is heated up to different temperatures(in

kevin).The Temperature at which the heated black-body radiator matches the color of the light source

is the color temperature of the light source.

6). Color Rendering Index(CR)

Color rendering index ranges from 0-100 ,measures a light source's ability to reproduce the color of various objects being lit by a reference light source, black body radiator(CRI=100)

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7). Efficacy(lm/W)

Eifficacy is the effciency of a light source to concert electricity energy to light energy which is expressed

in lumen output per unit power input (watt)

[Efficacy = lumen / wattage]

8). Design Life Time

Design life time is the average life of a lighting product when it is operated at nominal lamp voltage,current and controlled working environment. Actual lamp life varies because of any different

from those rating condition.

9). Dimmability

Not all lighting prodcuts is designed for dimming function. Dimming a non-dimmable LED lighting

product will cause un-predictable result and may affect the life time of the products.The below figure

shows the typical input current variation while adjusting the DC voltage input to dimmable and non-

dimmable product.

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Why LED Lighting Solution ?

Technology is changing lives at a pace never before witnessed in all of human history, and

with it, the way we see the world. More than a hundred years ago the incandescent filament

brought illumination to the night, multiplying human productivity at an exponential rate.

Later, fluorescent light rose up as a power-saving alternative to the incandescent.

And now there is a new source of light, once again on the cusp of transformational change -

OPTILED has seen the future, and it will no doubt be lit by Light Emitting Diodes, more

commonly known as LED. A low-power, high-efficiency technology created with non-toxic

materials, LED lamps are the next generation of lighting, leading the way into the green age

of illumination. Because LED lighting by OPTILED is safe, long-lasting and increasingly

cost-effective, it will play an important role in creating a more environmentally sustainable

future for many years to come.

OPTILED has touted the benefits of LED since long before it became cool to do so and

continues to work hard to change perceptions of LED technology. LED is no longer just a

niche product, and we have the expertise, technical knowhow, R&D and the people needed

to create the best general functional LED lighting solutions on the market.

There are a number of important reasons why OPTILED LED lighting is better than other

lighting technologies:

Longer life spans: OPTILED LED lamps last 35,000 hours - 30 times longer than

incandescent, 25 times longer than halogen and 10 times longer than compact fluorescent

lamps. Not only will you be helping the environment, you'll be saving money, too.

High Efficiency: Saves users up to 70% on energy usage compared to standard dichroic

low-wattage halogen and incandescent lamps, lowering electricity bills. An 5W LED MR16

bulb generates as much light as an 9W CFL, an 35W halogen, and 80% energy saving

compared to CFL downlight - A 15W LED downlight generates as much light as a 2x13W

CFL downlight and 75W incandescent bulb. Energy usage translates directly into significant

cost savings, especially in commercial applications where large quantities of lamps are

used.

Green lighting technology: Lower energy usage makes LED lighting better for the

environment, but it's a very green technology in other ways as well. Since no heat is

produced, it can reduce interior temperatures by 1-2 degrees, lowering air-conditioning

costs and CO2 emissions. LED lighting is also much safer for the environment because it is

mercury-free and doesn't produce IR or UV rays, which can be harmful to humans. In other

words, LED lamps are the greenest and most environmentally-friendly source of light on the

market.

Superior color, increased comfort: Clear light and high marks on the Color Rendering

Index (CRI), which indicates accurate true color reproduction, means LED lights produce

light that is more pleasing and relaxing, increasing comfort and mood.

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Industry Standards and Glossary

Like traditional lighting products, LED-based luminaires sold in the US are subject to industry standards governing safety and performance. To accommodate LEDs, some

existing standards and test procedures are being modified and new standards have been

developed.

LumaStream embraces the industry standards evolving on both federal and state

levels.

Within this rapidly evolving industry, the "language" for certain concepts, components, systems, applications, etc. is not well established and consistent throughout the industry.

This fact has created confusion between vendors, engineers, consumers, manufacturers,

and others. LumaStream believes it is important to define the language we use within our

company and throughout our website. As naming conventions become standardized we will

update these definitions.

Binning and labeling

is the process of separating LEDs based on their various characteristics and assigning them with a specific bin code. LEDs with the same characteristics are placed on a reel. White

LEDs are sorted by color and brightness. Color LEDs are sorted by dominant wavelength

and brightness. LumaStream relies on Philips, an industry partner, for precise binning

specs of the Philips Rebel chip.

CALiPER

is Department of Energy's (DOE) SSL Commercially Available LED Product Evaluation and

Reporting (CALiPER) program. CALiPER independently tests and provides unbiased

information on the performance of commercially available SSL products. Working in the public's interest, the DOE publishes test reports, technical information, and summaries of

manufacturer's products and is intended solely for the benefit of the public, in order to help

buyers, specifiers, testing laboratories, energy experts and others make informed decisions

about SSL products and related technologies.

CALiPER Program

Department of Energy's (DOE) SSL Commercially Available LED Product Evaluation and

Reporting (CALiPER) program independently tests and provides unbiased information on the performance of commercially available SSL products. Working in the public interest, the

DOE publishes test reports, technical information, and summaries of manufacturer's

products and is intended solely for the benefit of the public, in order to help buyers,

specifiers, testing laboratories, energy experts and others make informed decisions about

SSL products and related technologies. Manufacturers' products are selected randomly for

CALiPER program testing. CALiPER's main tests measure and assess (1) energy efficiency of SSL products, as specified

in IES LM-79 under luminaire efficacy, via this formula: Total lumens emitted by the

luminaire, divided by the total watts drawn by the luminaire's power supply; (2) thermal

management and the effect of temperature on lumen depreciation.

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Correlated Color Temperature (CCT)

is the measure used to describe the relative color appearance of a white light source. CCT indicates whether a light source appears more yellow/gold/orange or more blue, in terms of

the range of available shades of "white." CCT is measured in degrees Kelvin (unit of absolute

temperature). Cool White targets a typical CCT between 10,000K and 4500K; Neutral White,

between 4,500K and 3,500K; Warm White, between 3,500K and 2,540K.

Color Rendering Index (CRI)

indicates how well a light source renders colors of people and objects, compared to a

reference source of like color temperature.

Integration

is the "marrying" of lighting and lighting control components. Integration can set proper light levels and atmosphere for office video-conferencing, or create comfortable dynamic

scenes within a residential setting.

Interface

is the human mechanism for interacting with the lighting system; typically consisting of a

computer or a wall mounted control panel.

LED Light Engine

is a subsystem of an LED luminaire that includes one or more LED packages, an LED

array, or an LED module; an LED driver, electrical and mechanical interfaces; and an

integral heat sink to provide thermal dissipation. An LED light engine may be designed to accept additional components that provide additional aesthetic, optical, and environmental

controls. An LED light engine is designed to connect to the branch circuit.

LM-79

IESNA approved method for the electrical and photometric measurements of SSL. LM-79

specifies procedures for measuring total luminous flux, electrical power, luminous efficacy,

and chromaticity of SSL luminaires and replacement lamp products.

LM-80

IESNA approved method for measuring lumen maintenance of LED light sources. LM-80

specifies procedures for determining lumen maintenance of LEDs and LED modules (but

not luminaires) related to effective useful life of the product.

Lumen depreciation

is the decrease in lumen output that occurs as a lamp is operated. For most light sources, the lamp fails before significant lumen depreciation occurs; for example, a typical

incandescent bulb's lumen output will only decrease 10-15% over 1,000 hours of use, but

the bulb will fail at this time.* Because LEDs will continue to operate at very low light

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levels, LED life is usually defined as lumen depreciation to a particular point, such as 70%

of initial lumens

Luminous efficacy

is the most commonly used measure of the energy efficiency of a light source. It is stated in

lumens per watt (lm/w), indicating the amount of light a light source produces for each watt

of electricity consumed.

NEMA SSL-1 Power Supply

National Electrical Manufacturer's Association (NEMA) standard that specifies operational

characteristics and electrical safety of SSL power supplies and drivers.

Retrofit

means to substitute new or modernized systems for older lighting equipment. LumaStream

design-build systems can incorporate partial or complete retrofit and upgrade solutions.

Scalability

is a desirable property and benefit of a solid-state lighting system whereby capabilities can

be put in place to successfully accommodate future lighting needs. LumaStream systems

allow for expanding lighting needs and system control.

Scalable System

is a system designed to accommodate scalability, i.e. it can grow as the client's lighting or

control needs grow and change. LumaStream specializes in identifying whether our client's

systems need to be designed to accommodate scalability.

Solid-State Lighting (SSL)

refers to a type of lighting that uses light-emitting diodes (LEDs) as its source of

illumination.

TM-21

Lumen Depreciation Lifetime Estimation Method for LED Light Sources. TM-21 will provide

a method for determining an LED luminaire or integral replacement lamp's expected

operating life, based on initial performance data collected per IES-LM-80.

UL1598/8750A

UL standard for Luminaires - specifies the minimum safety requirements for luminaires.

The requirements in this document may be referenced in other documents such as UL8750

or separately used as part of the requirements for SSL products.

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UL1310/8750

UL standard for Class 2 Power Units - specifies the minimum safety requirements for Class 2 power supplies. (as defined by the National Fire Protection Association (NFPA), 70-2005)

UL-8750

Underwriters Laboratory (UL) has developed this safety standard for "Light Emitting Diode

(LED) Light Sources for Use in Lighting Products." Currently, UL has in place an "Outline of

Investigation" that references all existing UL standards applicable to LED lighting products.

The purpose of the outline is to provide a comprehensive approach and listing of applicable

standards for UL treatment of lighting products based on LEDs. The outline will be used until the full LED specific document is completed.

White Light

comprises light from all the frequency bands in the visible spectral range. Hence, it is a

combination of red, orange, yellow, green, blue, indigo, and violet.

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Achromatic

Describing the property of having no colour (or hue). For example a neutral white, grey or

black colour.

Additive Primary Colour

The additive primary colours are Red, Green & Blue. When equal amounts of light of the three additive primary colours is combined, white light is generated. Combining two additive

primaries in equal amounts creates a subtractive primary colour. See also: Subtractive

Primary Colour.

Angstrøm (Å)

A unit of wavelength of light. One Angstrøm (Å) is 0.1nm (or 1 x 10-10 m).

Average (Luminous) Intensity

Applies to LEDs. The near-field luminous intensity for a non point source. Defined in CIE

document 127 as being the intensity (luminous flux per unit solid angle) measured by a

photodetector with an input area of 100 mm2 positioned at either 316mm (condition A) or 100mm (condition B) from the tip of the LED source, measured on the mechanical axis of

the LED. Average luminous intensity has units of candela (cd). Not to be confused with

luminous intensity which is a far-field measurement of the luminous flux per unit solid

angle from a light source. See also: LED; Luminous Intensity; Luminous Flux; CIE; Far-

Field; Near-Field

Bandwidth

See Linewidth.

Barium Sulphate

A white pigment commonly used to coat the interior of integrating spheres and other reflecting chambers. Exhibits diffuse reflectance. Forms the basis of the following Labsphere

diffuse relfectance coatings: Spectraflect; Duraflect; and 6080.

Black

The (near) complete absorption of light as a result of no (low) reflectance. In colorimetry,

describes a colour of low saturation and low luminance.

Blackbody Radiation

Radiation that is full or complete, containing all wavelengths. The spectral power

distribution of light emitted from a blackbody is a function of its temperature only and is

described by Planck‟s law. See also: Colour Temperature.

Blackbody Radiator

A source that emits blackbody radiation.

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Brightness

That attribute of visual perception that describes the degree to which an object emits or

reflects light. In colorimetry, brightness is used in the HSB colour model – Hue, Saturation and Brightness. Describes the lightness of the colour, on a scale ranging from black to

white. Can be confused with saturation hence its use is discouraged. Can also be used

instead of luminance – again its use is not recommended. See also: Luminance.

Candela (cd)

The SI base unit used in photometry. The candela is the unit of luminous intensity. The

candela is one of the seven base units of the SI system. Since 1979, the candela has been

defined as: “the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 Hertz and has a radiant intensity in that

direction of 1/683 Watts per steradian” (where the steradian is the unit of solid angle). One

candela equals one lumen per steradian. See also: Luminous Intensity; Steradian.

Candela per Square Meter (cd/m2)

The SI unit of luminance. One cd/m2 equals one lumen per square meter per steradian. See

also: Luminance; Steradian.

Candle Power

The luminous intensity of a light source having units of candelas.

CCD

Acronym. Stands for Charge Coupled Device. A monolithic, two-dimensional semiconductor

(silicon-based) detector array. When illuminated by optical radiation in the range between approximately 300 and 1100nm, produces a photocurrent, the magnitude of which is

proportional to the level of light received. Each detector in the array is called a pixel.

CFL

Acronym. Stands for Compact Fluorescent Lamp.

Chroma

The lightness of a colour. Denotes the degree of lightness or darkness. See also: Lightness.

Chromatic

Described as having colour (or hue) – not white, grey or black.

Chromaticity

In colorimetry, describes the intensity or level of saturation of a colour (hue), defined as the

distance in the particular colour space of a colour from the neutral grey colour with the

same value.

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Chromaticity Coordinates (CIE)

A numeric descriptor of colour. Defined as the ratio of the three tristimulus values XYZ in

relation to the sum of the three, designated by xyz respectively. It is normal to assume that the chromaticity coordinates refer to the CIE 2° observer (1931). For reflected colour, it is

assumed to be calculated for standard illuminant C unless specified differently. See also:

(CIE) x, y; (CIE) u‟, v‟.

Chromaticity Diagram

The two-dimensional graph which plots the chromaticity coordinates. For the CIE 2°

observer (1931), x is plotted as the abscissa, y as the ordinate. The colour space plots the

spectrum locus of monochromatic radiation in the spectral range 380-770nm.

CIE

Acronym. From the French name "Commission Internationale de L'éclairage". In English this is the International Commission on Illumination. CIE sets the standards and provides

a worldwide forum for the exchange of information on the science of light, lighting, colour

and vision. Click here to visit the CIE's web site

CIE 1976 L*u*v* Colour Space

A uniform colour space adopted by CIE in 1976 that is used when measuring colour as a

result of additive mixing from emitters of light.

CIELAB

A uniform colour space adopted by CIE in 1976 within which L*a*b* colour coordinates are

plotted using a Cartesian coordinate system. This colour space plots equal colour differences at approximately equal distances. The L* value denotes the lightness, a*

represents the red/green axis, while b* represents the yellow/blue axis. CIELAB is that

colour space used in relation to the measurement of reflected or transmitted colour.

CIE Luminosity Function (Y)

See: Photopic Response.

CIE Standard Illuminant

Standard light source spectral power distributions as defined by CIE for several types of

light source. See Illuminant A, B, C, D, E & F.

CIE Standard Observer Function

See: Photopic Response; Scotopic Response; Tristmulus Response.

CMYK

Acronym. Stands for Cyan, Magenta, Yellow & blacK. See also: Subtractive Primary Colour.

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Colorimeter

An instrument that measures the colour of the light it receives. Applies to instruments that

measure reflected (transmitted) light as well as to those that analyse the light emitted by a source. Applies to instruments that use RGB optical filters to mimic the tristimulus colour

response of the human eye. See also: Tristimulus.

Colorimetry

The science of measuring the colour of light (emitted, reflected or transmitted) from an

object with a spectral response matching that of the human eye. See also: Tristimulus.

Colour

Can be described as being one aspect of an object‟s appearance. In colorimetry, colour is a

visual perception and is defined in respect of its hue, saturation and lightness.

Colour Difference

Being the size of the difference between two colours in a defined colour space.

Colour Rendering Index (CRI)

A metric which defines how well colours are rendered by different sources of illumination

compared to a defined standard illuminant. There are fourteen special colour rendering indices (Ri where i = 1-14) which define the colour rendering of the light source when used

to illuminate standard colours. The general colour rendering index (Ra) is the average of the

first eight special colour rendering indices (which correspond to non-saturated colours).

Colour Space

The three-dimensional solid enclosing all possible colours. The dimensions of the colour

space can be described in a number of different geometries, which leads to various spacings

within the colour space.

Colour Specification

Being the tristimulus values, chromaticity coordinates and luminance value (or other colour scale) that are used to uniquely describe a colour numerically.

Colour Temperature

Colour temperature defines the colour of radiation emitted from a perfect blackbody

radiator held at a particular temperature. Colour temperature is reported in units of Kelvin

(K). The plot of the chromaticity coordinates of a blackbody radiator with temperatures from

1,000 to 20,000 Kelvin is called the Planckian locus. Colours on this locus in the range

from 2,500 to 20,000 K are considered to be white, with 2,500 K being reddish white and

20,000 K being bluish white (warm to cool white). See also: Black Body Radiation; Correlated Colour Temperature.

Cone (Receptor)

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The visual receptor in the retina of the human eye responsible for daylight adapted, colour

vision. There are three types of cones, each sensitive to red, green or blue wavelengths. See

also: Retina; Rod.

Cornea

The transparent front part of the human eye. To use an engineering analogy, the cornea

functions as a "dust cap" and also performs primary focussing of the light rays into the eye.

Correlated Colour Temperature (CCT)

Correlated Colour Temperature (CCT) describes the colour temperature of those white light

sources whose colours don‟t fall exactly on the Planckian locus (i.e. for non blackbody emitters). The CCT of a non-Planckian source is the blackbody colour temperature that the

source resembles most closely. Correlated colour temperature is reported in units of Kelvin

(K). CCT can be considered to be a simplified metric for describing the colour of a white light

source. For coloured light sources, dominant wavelength can be used to express colour in a

single number. See also: Colour Temperature; Dominant Wavelength.

Cosine Diffuser

An object which exhibits Lambertian like reflectance or transmittance. Transmission diffusers are used in photometry to impart a cosine response at the input to a detector to

correct for the effective illuminance of off-axis rays, or to more uniformly illuminate a multi-

element detector. Thin sheets of ground glass (quartz), PTFE as well as the input port of an

integrating sphere all function as effective transmission diffusers. See also: Cosine

Response.

Cosine Response

The Lambertian spatial response of a perfect reflecting or transmitting diffuser whereby the intensity from or through the surface varies with the cosine of the angle subtended between

the direction of view and the normal to the surface. Applies to light meters (radiometers and

photometers) designed for measuring irradiance or illuminance which should apply a cosine

angular response to light rays received at angles other than normal incidence, typically

achieved using a transmission diffuser or integrating sphere. See also: Cosine Diffuser;

Lambertian.

CRT

Acronym. Stands for Cathode Ray Tube. The type of television display that was popular before the introduction of flat panel displays (LCD, OLED, RPTV & plasma).

Diode Array

A detector that comprises a linear array of segmented photodiode detectors. See also:

Photodetector; Photodiode; Spectroradiometer.

Dominant Wavelength

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Dominant wavelength is a useful measure of the effective wavelength (in nm) of non-

monochromatic light sources, in particular LEDs. It is defined in relation to a specified

standard illuminant (usually Illuminant E, but this is arbitrary). It is a measure of the hue

(or colour sensation) produced by the light source. Not to be confused with peak

wavelength. Dominant wavelength is normally applied to coloured LEDs whereas correlated colour temperature is applied to white LEDs.

Duraflect

Labsphere's proprietary, waterproof, diffuse white coating for the UV-VIS-NIR spectral

region (350-1200nm).

Electroluminescence

The emission of light as a result of the passage of an electrical current. Distinct from

incandescence which is the emission of light as a result of heat. See also: LED.

Electromagentic Radiation

Electromagnetic radiation is generated by the motion of electrically charged particles.

Optical radiation, light, X-rays, radio waves and microwaves are all examples of

electromagnetic radiation. See: Light; Optical Radiation.

EULUMDAT (File)

A standardised data file which expresses the light output of a luminaire as luminous intensity versus angle. EULUMDAT files are assigned the file extension ".ldt". Used by

lighting designers to model the illumination performance of a lighting scheme using

commercial lighting design programmes. An EULUMDAT file is commonly referred to as

"photometric data" for a luminaire. See also: Goniophotometer; IES (file).

Far Field

In photometry, that distance from a lamp (called the photometric distance) where the

emitter is considered to be a point source, usually at a distance of between 5-10 times the source diameter (although this is not the case for LEDs). Intensity measurements are

performed in the far field, in which the inverse squared law applies. See also: Near Field;

Intensity; Average Intensity; Inverse Squared Law; Point Source; Photometric Distance.

Fluorescence

The emission of light at a longer wavelength as a result of absorption of light at a shorter

wavelength in a fluorescent material. Applies for that case whereby the emission occurs at

the same time as the absorption. See also: Luminescence; Phosphorescence.

Fluorescent Lamp

A lamp comprising a glass tube filled with mercury gas and coated on its inner surface with a phosphor. When the gas is charged with an electrical current, ultraviolet radiation is

produced. This in turn is absorbed in the phosphor, causing it to emit visible light by the

process of fluorescence. See also: CFL; Fluorescence.

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Foot-candle (fc)

The English unit of illuminance. One foot-candle (fc) equals one lumen per square foot,

which equals 10.76 lux. See also: Illuminance; Lux.

Foot-Lambert (fL)

The English unit of luminance. One foot-Lambert (fL) equals 1/π candelas per square foot, which equals 3.426 candelas per sq. meter. See also: Luminance.

Fovia

That part of the eye‟s retina that has the greatest density of cones. See also: Retina, Cone.

Goniometer

A goniometer is an (electro) mechanical positioning device which allows one to change the

relative angle (φ, θ) at which a photometer (also a spectroradiometer or colorimeter) views a

light source. This can be accomplished by either moving the detector around a stationary

source or by tipping and tilting the source whilst the detector remains in a fixed position.

See also: Goniophotometer.

Goniophotometer

An instrument which performs measurements of the (far-field) luminous intensity or illuminance or (near-field) luminance of a light source as a function of viewing angle. Can

also be used to measure the total luminous flux of a light source by measuring the

directional luminous intensity and integrating over 4π steradians. A goniophotometer is

commonly used to measure so-called "photometric data" for luminaires. Photometric data in

this context is the light output (luminous intensity) as a function of angle presented in industry-standard file formats. See also: EULUMDAT; Goniometer; IES.

Hue

The perceived colour of a light source.

IES (File)

A standardised data file which expresses the light output of a luminaire as luminous

intensity versus angle. Derives from the acronym for the Illuminating Engineering Society of

North America (IESNA). IES files are assigned the file extension ".ies". Used by lighting

designers to model the illumination performance of a lighting scheme using commercial

lighting design programmes. An IES file is commonly referred to as "photometric data" for a

luminaire. See also: EULUMDAT (file); Goniophotometer.

Illuminance

Illuminance (Ev) is the luminous flux received per unit area. Illuminance is measured in lux

(lx) where 1 lux equals 1 lumen per square meter. See also: Foot-candle.

Illuminant A

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Illuminant A (CIE) represents the colour temperature of an incandescent lamp (2856K). See

also: Standard Illuminant; Colour Temperature.

Illuminant B

Illuminant B (CIE) represents the colour temperature of direct sunlight (4874K). See also:

Standard Illuminant; Colour Temperature.

Illuminant C

Illuminant C (CIE) represents the colour temperature of indirect sunlight (6774K). See also:

Standard Illuminant; Colour Temperature.

Illuminant D

Illuminant D (CIE) represents the colour temperature of daylight. There are several standard illuminants in the D series including D50 which represents bright incandescent

light (5000K) and D65 which represents natural daylight (6504K). See also: Standard

Illuminant; Colour Temperature.

Illuminant E

Illuminant E (CIE) is the colour temperature of an artificial, normalising source (5500K).

Has chromaticity coordinates of x=0.3333 & y=0.3333. See also: Standard Illuminant;

Colour Temperature.

Illuminant F

Illuminant F (CIE) represents the correlated colour temperature of light from a fluorescent

lamp. There are several standard illuminants in the F series including F2 which represents cool white light (4200K), F7 which represents broadband daylight (6500K) and F11 which

represents a narrow band white lamp (4000K). See also: Standard Illuminant; Colour

Temperature.

Imaging Photometer (Colorimeter)

A photometric instrument capable of spatially-resolved luminance, illuminance and colour

measurements. Sometimes referred to as a video photometer. Employs a CCD detector.

Incandescence

Light that is emitted by thermal radiation at a temperature high enough to be visible.

Incandescent Lamp

A lamp which emits light as a result of resistive heating when an electrical current passes

through a metal wire in a vacuum.

Infragold

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Labsphere's proprietary electro-plated gold coating for the infrared spectral region

(>800nm).

Infrared

Describing that part of the electromagnetic spectrum comprising optical radiation having

wavelengths longer than 780nm but shorter than 1mm. Infrared radiation is not visible to

the naked eye.

Integrating Sphere

A hollow, spherical chamber with a diffuse, high reflectance interior coating. Used in

photometry to measure the total luminous flux (power) of a light source.

Intensity

See: Luminous Intensity

Inverse Squared Law

Describes the relationship between the illuminance from a light source which varies in

inverse proportion to the square of the distance from the source. Applies to the case of a

point source of light in the photometric far-field. See also: Far-Field; Illuminance; Point

Source.

Iris

The variable, limiting aperture found in the human eye.

Irradiance

Irradiance (Ee) is the radiometric analogue of illuminance, the radiant flux received per unit

area. Irradiance is measured in Watts per square meter.

Isotropic

A light source is isotropic when it radiates with equal intensity (flux per unit solid angle) in

all directions. Not to be confused with Lambertian.

Kelvin (K)

The unit of measurement of colour temperature and correlated colour temperature. The Kelvin scale starts at absolute zero (-273°C). See also: Colour Temperature; Correlated

Colour Temperature.

Lambert's Cosine Law

See Lambertian.

Lambertian

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A Lambertian surface is one that reflects (or transmits) with equal radiance or luminance in

all directions. In other words, the reflected (transmitted) intensity (flux pew unit solid angle)

from a Lambertian surface varies in proportion to the cosine of the angle subtended

between the direction of view and the surface normal. See also: Cosine Response.

Laser

From the acronym for Light Amplification by the Stimulated Emission of Radiation. A light

source typically characterised by a combination of coherence, narrow spectral linewidth and a collimated beam. The term "laser light" refers to electromagnetic radiation with

wavelengths between 150nm up to 11µm. A laser was first demonstrated in 1960 by

Theodore H Maiman working at the Hughes Corporation, although the term „laser‟ was first

coined by Gordon Gould of Columbia University.

LCD

Acronym. Stands for Liquid Crystal Display.

LED

Acronym. Stands for Light Emitting Diode. LEDs are solid state light sources which

generate light by electroluminescence when an electrical current is passed through a semiconductor p-n junction. See also: Electroluminescence; OLED.

Light

Light is a term that we use to define that part of the electromagnetic radiation that humans

can see (“visible light”). Visible light has a wavelength bteween 380 and 780nm. More

accurately described as optical radiation, it forms part of the electromagnetic spectrum that

encompasses radio waves, microwaves, x-rays and gamma rays. Optical radiation is that

which obeys wave-like behaviour, as opposed to particle-like.

Lightness

See Chroma.

Linewidth

Denotes the spectral purity or width in wavelength of a light source. The spectral width of a light source is normally defined as the full width half max (FWHM) linewidth. The term

bandwidth is often used interchangeably with linewidth.

LOR

Acronym. Stands for Light Output Ratio. Being the ratio of the luminous flux produced by a

luminaire to that produced by the lamp (or lamps) fitted to the luminaire. A measure of the

efficiency of a luminaire. See also: Luminaire; Luminous Flux.

Lumen (lm)

The SI unit of luminous flux (lm).

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Luminaire

A light fitting which generally comprises a lamp in a housing together with a reflector

and/or lens. May include control gear (drive electronics).

Luminance

Luminance (Lv) is the luminous flux emitted per unit solid angle and per unit area. In the SI

system, luminance is measured in candelas per square meter where 1 cd/m2 equals 1

lumen per steradian per square meter. The photometric analogue of radiance. Luminance is

a near-field measurement of a light source; luminous intensity is the measurement made in

the photometric far-field. See also: Far-Field; Foot-Lambert; Luminous Intensity; Near-Field;

Nit; Steradian.

Luminescence

Luminescence can be taken to describe the process of fluorescence or phosphorescence.

See: Fluorescence, Phosphorescence.

Luminous Efficacy

The efficiency of a light source, the quotient of the luminous flux emitted divided by the electrical power consumed. Reported in units of lumens per Watt (lm/W).

Luminous Exitance

Luminous exitance (Mv) is the luminous flux emitted from a surface per unit area, measured

in units of lumens per square meter. Geometrically equivalent to illuminance, luminous

exitance is not however reported in lux.

Luminous Flux

The luminous flux (Fv) or more correctly the total luminous flux of a light source is the total

photometric power emitted in all directions. Luminous flux is measured in lumens (lm),

which is the photometric analogue of the Watt.

Luminous Intensity

The luminous intensity (Iv) in a given direction (often abbreviated to intensity, sometimes

referred to as beam candela) is the photometric power from a point source emitted per unit solid angle. Intensity is measured in the SI base unit of the candela (cd) where 1 candela

equals 1 lumen per steradian. Luminous intensity is a far-field measurement of a light

source; luminance is the measurement made in the photometric near-field. See also: Far-

Field; Luminance; Near-Field; Steradian.

Lux (lx)

The SI unit of illuminance (lx).

Mean Spherical Candle Power (MSCP)

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Mean Spherical Candle Power (M.S.C.P.) is the luminous flux of a light source divided by 4π

steradians.

Mesopic

Photopic (cone) vision operates when the eye sees luminance levels of ≥ 3 candelas per

square meter, whereas scotopic (night time) vision operates when the luminance falls below

0.01 candelas per square meter. For luminance levels between 0.01 and 3 cd/m2, both rods

and cones contribute to the vision process to varying degrees. This "in-between" region is called mesopic, and research is ongoing into the development of a standard observer

function for mesopic vision. See also: Photopic; Scotopic.

Micrometer (µm)

A unit of wavelength, normally used to describe infrared radiation. Often abbreviated

to 'micron'. One micrometer or micron (µm) equals 1 x 10-6 meters. One micrometer also

equals 1000 nanometers (nm).

Monochromatic

Light that is composed of a single wavelength or colour (hue), having 100% purity and a

narrow linewidth.

Monochromator

See Spectrometer.

Nanometer (nm)

A unit of wavelength of light, normally used to describe visible light. One nanometer (nm) equals 10-9 meters.

Near-Field

In photometry, that region close to a lamp where the emitter is not considered to be a point

source, usually at a distance of less than 5-10 times the source diameter (although this is

not the case for LEDs). Intensity measurements are performed in the far field, in which the

inverse squared law applies. See also: Far Field, Intensity, Average Intensity, Inverse

Squared Law, Point Source.

Nit

A historically significant unit of luminance. Derives from the Latin "to illuminate". One nit equals 1 candela per square meter. See also: Luminance.

OLED

Acronym. Stands for Organic Light Emitting Diode. A type of light emiting diode (LED) with

an emissive electroluminescent layer made of organic compunds. Related devices are Light

Emitting Polymers (LEPs). See also: Electroluminescence; LED.

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Optical Density (OD)

Describes the level of attenuation of light as it passes through an optical filter. The higher

the OD value, the higher the attenuation (and the higher the protection). OD increases with increasing thickness of absorptive filters. Optical density is the logarithm (to the base ten)

of the reciprocal of the transmittance. For example, an OD of 1 means 10%, an OD of 2

means 1% and an OD of 3 means 0.1% transmittance (and so on)

Optical Radiation

Describing that part of the electromagnetic spectrum comprising rays that exhibit a wave-

like property (as opposed to particle-like). Includes ultraviolet, visible (light) and infrared

radiation.

Phosphorescence

The emission of light at a longer wavelength as a result of absorption of light at a shorter wavelength in a phosphorescent material. Applies for that case whereby the emission

occurs after the absorption. See also: Fluorescence, Luminescence.

Photodetector

A generic name given to a device that detects optical radiation. See also: Photodiode;

PMT; Diode Array; CCD.

Photodiode

A discrete semiconductor photodetector that produces a photocurrent the magnitude of

which is proportional to the level of light received when illuminated by optical radiation. In

photometers, the detector is based on silicon with a photopic filter; the combined detector plus filter is designed to provide a spectral responsivity scaled to match that of the photopic

response, the CIE standard observer for photopic vision.

Photometric Distance

That distance from a light source that defines the far field. In the photometric far-field,

illuminance (irradiance) varies in inverse proportion to the square of the distance form the

light source. See also: Inverse Squared Law; Far-Field; Near-Field.

Photometer

An optical instrument that measures a defined geometric property of visible light with a

photopic spectral response matching that of the human eye. See also: Photopic;

Radiometer; Spectroradiometer.

Photometry

The science of measuring optical radiation with a photopic spectral response matching that of the human eye. See also: Photopic; Radiometry; Spectroradiometry.

Photomultiplier Tube (PMT)

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A photomultiplier tube (PMT) is a photodetector that comprises a photocathode which is

held in vacuum and emits electrons when exposed to light. This charge is accelerated by a

high voltage field causing the electrons to hit a metal plate, whereupon more electrons are

emitted (the multiplier effect). Not normally used in photometers, PMTs are commonly used

in traditional scanning spectroradiometer (monochromator) systems.

Photopic (Response)

The daylight-adapted relative spectral response of the eye is called the spectral luminous efficiency function for photopic vision, V(l). This is an empirical distribution that was first

adopted in 1924. Applies for luminance values above 3cd/m2 to the spectral range between

380 and 780nm having a peak response at 555nm. The photopic response explains why the

human eye is more sensitive to green light than blue or red light. At luminance levels below

3cd/m2, the eye transitions through a mesopic response. At luminance levels at or below 0.01 cd/m2, the eye becomes dark adapted and possesses a scoptic response. See also:

Mesopic; Scotopic.

Pixel

The individual detector element in a two-dimensional CCD detector array. See also: CCD.

Plankian Locus

The locus of points on the CIE chromaticity diagram that plots the chromaticity of

blackbody radiators of differing colour temperatures.

Plankian Radiator

A synonym for blackbody radiator.

Point Source

A light source is considered to be a point source if it is observed at a position at or beyond

the photometric distance, that is, the far-field. See also: Intensity; Average Intensity; Far-

Field; Photometric Distance.

Polychromatic

Used to describe optical radiation that is comprised of multiple discrete wavelength or having a continuous spectrum.

Primary Colour

In colorimetry, primary (additive) colours are red, green and blue, and their subtractive

opposites cyan, magenta and yellow. See also: Additive Primary Colours; Subtractive

Primary Colours.

Purity

Purity is a measure of the degree of saturation of a light source, reported as a percentage. It

is defined with respect to a specified standard illuminant (usually illuminant E, but this

24 | P a g e


arbitrary). As most (coloured) LEDs have a narrow spectral emission (that is, near-

monochromatic), they have a purity of close to 100% (in other words, the colour cannot be

distinguished from a true monochromatic light source). See also: Saturation.

Radiance

Radiance (Le) is the radiant flux emitted per unit solid angle and per unit area. Radiance is

measured in Watts per steradian per square meter. The radiometric analogue of luminance.

Radiant Exitance

Radiant exitance (Me) is the radiant flux emitted from a surface per unit area, measured in

units of Watts per square meter. Geometrically equivalent to irradiance and the radiometric analogue of luminous exitance.

Radiant Flux

The radiant flux (Φe) - more correctly the total radiant flux - of a light source is the total

power emitted in all directions. Radiant flux is measured in Watts (W), which is the

radiometric analogue of the lumen.

Radiant Intensity

The radiant intensity (Ie) in a given direction (often abbreviated to intensity) is the radiant

flux from a point source emitted per unit solid angle. Intensity is measured in units of

Watts per steradian. The radiometric analogue of luminous intensity.

Radiometer

An optical instrument that measures the absolute amount of a defined geometric property

of light. A laser power meter is a type of radiometer. See also: Photometer; Spectroradiometer.

Radiometry

The science of measuring the absolute amount of optical radiation.

Retina

The light-sensitive area on the rear of the human eye containing photo-receptors. The area

containing the highest concentration of photo-receptors is called the fovea. See also: Rod;

Cone; Fovea.

RGB

Meaning Red, Green & Blue which are the additive primary colours. Used in relation to the

human eye‟s tristimulus colour response. See also: Additive Primary Colour.

Rod

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The visual receptor in the retina of the human eye responsible for scotopic (night-time,

monochromatic) vision. See also: Retina; Cone.

Saturation

The attribute of colour perception that describes the degree of departure of the colour from

the neutral grey of the same lightness. See also: Purity.

Scotopic

The dark-adapted relative spectral response of the eye is called the spectral luminous

efficiency function for scotopic vision, V‟(l). The scotopic response was first adopted by CIE

in 1951 and applies to the spectral region between 380 and 780nm, with a peak at 507nm. The Scotopic response applied to luminance levels of 0.01 cd/m2 of less. See also: Mesopic;

Photopic.

SI

Systeme Internationale d‟Unites, the international metric system of measurement units.

Silicon Photodiode

See Photodiode.

Solid Angle

See Steradian.

Spectral Power Distribution (SPD)

The power distribution of a light source as a function of wavelength. Determines the colour,

colour temperature and colour rendering properties of a light source.

Spectraflect

Labsphere's proprietary white reflectance coating. The coating is barium sulphate based

and hydroscopic. Available as a coating service and as a liquid paint (6080) for user application. Best applied by spray painting.

Spectralon

Labsphere's patented diffuse reflectance material. A solid thermoplastic which exhibits the

highest diffuser reflectance of any material in the 250-2500nm range. Integrating spheres

and reflectors are machined from a block of Spectralon. Spectralon is widely used as a

white reflectance standard (99%). Can be doped with inorganic materials to create grey

scale standards (2-80%), colour standards, wavelength standards and fluorescence

standards.

Spectrometer

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An instrument that separates polychromatic light into its constituent wavelengths. Employs

a dispersive optical element, usually a diffraction grating. A spectroradiometer and a

spectrophotometer comprise a spectrometer combined with a detector, normally a CCD

array. A (scanning) monochromator is a form of spectrometer in which the diffraction

grating rotates to transmit one wavelength at a time, whereas a CCD spectrometer analyses a wide range of wavelengths simultaneously.

Spectroradiometer

An instrument for measuring the radiant power from a light source as a function of

wavelength. Normally combines a spectrometer with a photodetector or CCD. Can be used

to more accurately calculate the photometric and colorimetric properties of a light source

than a photometer or colorimeter by multiplying the spectral radiant power by standard

photopic and tristimulus observer functions.

Spectrum

The spectral arrangement of electromagnetic energy in order of wavelength. See also: Spectral Power Distribution (SPD).

Spectrum Locus

The plot of the chromaticity coordinates of monochromatic light in the CIE colour space

diagram. See also: Chromaticity Diagram (CIE).

Standard Illuminant

See CIE Standard Illuminant.

Standard Observer

See: CIE Standard Observer Function.

Steradian

The steradian is the (dimensionless) unit of solid angle. A sphere contains 4π steradians

(and by definition, a hemisphere comprises 2π steradians). A steradian is that solid angle

subtended from the centre of a sphere by a spherical surface area having an area equal to

the square of the radius. In other words, the steradian solid angle of a beam of light is equal to the projected area divided by the square of the distance.

Subtractive Primary Colour

The subtractive primary colours are Cyan, Magenta & Yellow. When inks of these colours

are applied to white paper in equal amounts, these combine to produce black. Combining

two subtractive primaries in equal amounts creates an additive primary colour. See also:

CMYK; Additive Primary Colour.

Thermopile

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A broadband detector (thermal rather than optical) that is commonly used in the radiometry

of lasers. Comprises an array of thermocouple junctions.

Tristimulus

Describing the RGB 2° colour matching functions, which CIE transformed into the XYZ

colour matching functions. The XYZ functions define the CIE 1931 standard colorimetric

observer. The Y channel (green) was chosen to match that of the photopic response, so that

colour measurement instruments could double as photometers. For observer fields of view of greater than 2°, CIE published its 1964 supplementary standard colorimetric observer.

(CIE) u' Chromaticity Coordinate

Together with the CIE v' chromaticity coordinate provides a numeric description of colour.

The CIE u' chromaticity coordinate is plotted as the abscissa (horizontal axis) on the two-

dimensional colour space graph defined by CIE to communicate the colour of a light source.

The CIE v' chromaticity coordinate is plotted as the ordinate (vertical axis). Refers to the CIE

10° tristimulus observer function (1964) as plotted in the 1976 uniform colour space chromaticity diagram. The intersection of u' and v' within the CIE colour space diagram

uniquely defines the colour of a light source. See also: Chromaticity Coordinates;

Chromaticity Diagram; Tristimulus; (CIE) x; (CIE) y.

Ultraviolet (UV)


wavelengths between 100 and 400nm. Ultraviolet (UV) radiation is absorbed in the lens or

cornea and is not visible to the naked human eye.

UVA

That part of the Ultraviolet spectral range with wavelengths between 315 and 400nm.

UVB


UVC


(CIE) v' Chromaticity Coordinate

Together with the CIE u' chromaticity coordinate provides a numeric description of colour. The CIE v' chromaticity coordinate is plotted as the (vertical axis) on the two-dimensional

colour space graph defined by CIE to communicate the colour of a light source. The CIE u'

chromaticity coordinate is plotted as the abscissa (horizontal axis). Refers to the CIE 10°

tristimulus observer function (1964) as plotted in the 1976 uniform colour space

chromaticity diagram. The intersection of u' and v' within the CIE colour space diagram uniquely defines the colour of a light source. See also: Chromaticity Coordinates;

Chromaticity Diagram; Tristimulus; (CIE) x; (CIE) y.

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Visible (Light)


wavelengths between 380 and 780nm that can be detected by the retina in the human eye. Wavelengths in this range combine to create the sensation of colour.

V(λ) Function

See Photopic.

Watt (W)

The SI unit of power and radiant flux.

Wavelength

The periodic peak-to-peak distance in an electromagnetic wave. For ultraviolet and visible

light, defined in nanometers (nm); for infrared light, defined in micrometers (µm).

White Light

Light that appears to be white. Can contain a continuous spectrum of light (as from the

sun) or comprise as few as two colours. White light comprising two colours exhibits poor

colour rendering. Light on the Planckian locus (blackbody curve) on the CIE chromaticity

diagram with colour temperatures between 2500 and 20000K is considered to be “white”. See also: CIE Standard Illuminant.

(CIE) x Chromaticity Coordinate

Together with the CIE y chromaticity coordinate provides a numeric description of colour.

The CIE x chromaticity coordinate is plotted as the abscissa (horizontal axis) on the two-

dimensional colour space graph defined by CIE to communicate the colour of a light source.

The CIE y chromaticity coordinate is plotted as the ordinate (vertical axis). Refers to the CIE

2° tristimulus observer function (1931). The intersection of x and y within the CIE colour space diagram uniquely defines the colour of a light source. See also: Chromaticity

Coordinates; Chromaticity Diagram; Tristimulus; (CIE) u'; (CIE) v'.

(CIE) y Chromaticity Coordinate

Together with the CIE x chromaticity coordinate provides a numeric description of colour.

The CIE y chromaticity coordinate is plotted as the (vertical axis) on the two-dimensional

colour space graph defined by CIE to communicate the colour of a light source. The CIE x

chromaticity coordinate is plotted as the abscissa (horizontal axis). Refers to the CIE 2°

tristimulus observer function (1931). The intersection of x and y within the CIE colour space diagram uniquely defines the colour of a light source. See also: Chromaticity

Coordinates; Chromaticity Diagram; Tristimulus; (CIE) u'; (CIE) v'.

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Lumen Method Calculations

The lumen method is based on fundamental lighting calculations. The lumen method

formula is easiest to appreciate in the following form.

(1)

where E = average illuminance over the horizontal working plane

n = number of lamps in each luminaire

N = number of luminaire

F = lighting design lumens per lamp, i.e. initial bare lamp luminous

flux

UF = utilisation factor for the horizontal working plane

LLF = light loss factor

A = area of the horizontal working plane

2.1 Light Loss Factor

Light loss factor (LLF) is the ratio of the illuminance produced by the lighting

installation at the some specified time to the illuminance produced by the same installation when new. It allows for effects such as decrease in light output caused by

(a) the fall in lamp luminous flux with hours of use,

(b) the deposition of dirt on luminaire, and

(c) reflectances of room surfaces over time.

In fact, light loss factor is the product of three other factors:

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(2)

where LLMF = lamp lumen maintenance factor

LMF = luminaire maintenance factor

RSMF = room surface maintenance factor

2.1.1 Lamp Lumen Maintenance Factor

Lamp lumen maintenance factor (LLMF) is the proportion of the initial light output of

a lamp produced after a set time to those produced when new. It allows for the decline

in lumen output from a lamp with age. Its value can be determined in two ways:

(a) by consulting a lamp manufacturer's catalog for a lumen depreciation chart, and

(b) by dividing the maintained lumens by the initial lamps.

2.1.2 Luminaire Maintenance Factor

Luminaire maintenance factor (LMF) is the proportion of the initial light output from a luminaire after a set time to the initial light output from a lamp after a set time. It

constitutes the greatest loss in light output and is mainly due to the accumulation of

atmospheric dirt on luminaire. Three factors must be considered in its determination:

(a) the type of luminaire,

(b) atmospheric conditions, and

(c) maintenance interval.

2.1.3 Room Surface Maintenance Factor

Room surface maintenance factor (RSMF) is the proportion of the illuminance

provided by a lighting installation in a room after a set time compared with that

occurred when the room was clean. It takes into account that dirt accumulates on room surfaces and reduces surface reflectance. Figure 4 shows the typical changes in

the illuminance from an installation that occur with time due to dirt deposition on the

room surfaces.

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2.2 Utilisation Factor

Utilisation factor (UF) is the proportion of the luminous flux emitted by the lamps

which reaches the working plane. It is a measure of the effectiveness of the lighting scheme. Factors that affect the value of UF are as follows:

(a) light output ratio of luminaire

(b) flux distribution of luminaire

(c) room proportions

(d) room reflectances

(e) spacing/mounting height ratio

2.2.1 Light Output Ratio of Luminaire

Light output ratio of luminaire (LOR) takes into account for the loss of light energy

both inside and by transmission through light fittings. It is given by the following

expression.

(3)

Example 1

The total, upward and downward lamp output from a lamp are 1000 lm, 300 lm and

500 lm respectively. Calculate upward light output ratio (ULOR), downward light output ratio (DLOR), light output ratio (LOR) of luminaire and percentage of light

energy absorbed in luminaire.

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Amount of light energy absorbed in luminaire = 100 - 80 = 20 %

A greater DLOR usually means a higher UF.

A simple classification of luminaires according to their distribution is based on flux

fractions, as shown in Figure 5. Upward flux fraction (UFF) and downward flux

fraction (DFF) are used as a basis of comparison.

Example 2

For data given in Example 1 determine upward flux fraction (UFF), downward flux fraction (DFF) and flux fraction ratio (FRR).

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Figure 5 Flux Fraction of Various Luminaires

2.2.2 Flux Distribution of Luminaire

Direct ratio is the proportion of the total downward luminous flux from a conventional

installation of luminaires which his directly incident on the working plane. It is used to assess the flux distribution of luminaire. Since the intensity distribution pattern of the

light radiated from a luminaire in the lower hemisphere will affect:

(a) the quantity of the downward flux falls directly on the working plane and

(b) the quantity of flux available for reflection from the walls in a given room,

Direct ratio depends on both the room proportions and the luminaires. Direct ratio has a low value with a narrow room (small room index) and a luminaire which emits

most of its light sideways (BZ 10), and on the contrary, a high value with a wide room

(large room index) and a luminaire which emits most of its light downwards (BZ 1).

2.2.3 Room Proportion

Room index (RI) is the ratio of room plan area to half the wall area between the

working and luminaire planes.

(4)

where L = length of room

W = width of room

Hm = mounting height, i.e. the vertical distance between the working plane and the

luminaire.

2.2.4 Room Reflectances

The room is considered to consist of three main surfaces:

(a) the ceiling cavity,

(b) the walls, and

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(c) the floor cavity (or the horizontal working plane).

The effective reflectances of the above three surfaces affect the quantity of reflected

light received by the working plane.

2.2.5 Spacing to Height Ratio

Spacing to Height ratio (SHR or S/Hm) is defined as the ratio of the distance between

adjacent luminaires (centre to centre), to their height above the working plane. For a

rectangular arrangement of luminaires and by approximation,

(5)

where A = total floor area

N = number of luminaires

Hm = mounting height

Under a regular array of luminaires the illuminance on the working plane is not uniform. The closer spaced the luminaires for a given mounting height, the higher the

uniformity; or the greater the mounting height for a given spacing, the greater the

uniformity. If uniformity of illuminance is to be acceptable for general lighting,

(a) SHR should not exceed maximum spacing to height ratio (SHR MAX) of the given luminaire as quoted by the manufacturer, and

(b) geometric mean spacing to height ratio of the luminaire layout should be within the

range of nominal spacing to height ratio (SHR NOM) of the given luminaire as quoted

by the manufacturer, i.e.

(6)

jwn student notes

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