vi. terminology for display - hallym.ac.kr · 2015-04-10 · •radiometry: a set of techniques for...

VI. Terminology for Display

Special Topics in Display Technology 1st semester, 2015

* Reference books:

[Light Measurement Handbook] (http://www.intl-light.com)

[응용광학] (두양사) 21장

http://www.intl-light.com/

Contents

Radiometry and PhotometryLuminous FluxLuminous ExitanceIlluminanceLuminous IntensityLuminance

Several Aspects of PhotometryInverse Square LawLambertian SurfaceViewing-Angle Properties

MeasurementLuminous FluxIlluminance

• radiometry: a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye.• photometry: the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power.

Radiometry and Photometry

• In photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Typically, this weighting function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way.

Solid Angle

2-dimensional angle 3-dimensional solid angle

l

q

r

(radian)l

rq

2

2

2 2

(steradian, sr)

44 (sr)total

Surface

dAd

r

dA r

r r

The solid angle is the angle in the 3-dimensional space that an objectsubtends at a point. It is a measure of how big thatobject appears to an observer lookingfrom that point.

[Examples]

(1) If we look at the moon from the earth, what is the solid angle formed by our eyes and the area of the moon?

(2) Consider that an incandescent lamp is hung down from a ceil. The height of this lamp is 2 m. If we can assume this lamp to be a point source, what would be the solid angle formed by this lamp and the book you are holding by your hands. The area of the book is 30cm*40cm.

The nonpoint and/or nonuniform light sources may be treated as composedof small differential point sources, or the entire source can be observed at alarge distance so that its luminous flux may be considered as radiating from apoint.

555 nm, 1W - 683 lm

• fe (radiant flux): radiant energy per unit time, also called radiant power. (W)

복사측정학

측광학

• luminous efficacy: luminous power per unit input power (lm/W)

Luminous Flux

• fv (luminous flux or luminous power): the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.

[Example] (1) 1 lm of the light at 555 nm equals to 1/683 W. What is the watt of 1 lm at 630

nm?

(2) We have three lasers of which the wavelengths are 450 nm, 555 nm, 650 nm. If the output power of each lasers is 10 W, what is the total lumen?

복사측정학

측광학

• M (exitance): power emitted from a unit surface.

Me = fe / A (W/m2)

Mv = fv / A (lm/m2)

Luminous Exitance

• radiant exitance: radiant power emitted from a unit surface.

• luminous exitance: luminous power emitted from a unit surface.

복사측정학

측광학

• E (irradiance): radiant power incident on a unit surface, also called radiant flux density.

Ee = fe / A (W/m2)

• E (illuminance): luminous power incident on a unit surface, also called radiant flux density.

Ev = fv / A (lm/m2 = lux (lx))

Irradiance

Illuminance

복사측정학

• radiant intensity: radiant power per unit solid angle. (W/sr)

Ie = fe / w (W/sr) (w: solid angle)

측광학

• luminous intensity: luminous power per unit solid angle. (lm/sr = candela)

Iv = fv / w (lm/sr = cd)

Luminous Intensity

• LED: NSCW 215T (Nichia Co.Ltd)

Luminous Intensity Distribution

• Incandescent lamp

Example

1 cd

1 m

luminous flux?

illuminance?

2 m60o

area: 100 cm2

illuminance?

복사측정학

• radiance: radiant power per unit solid angle per unit projected source area.

Le = fe / (Acosq) w = Ie / Acosq (W/sr*m2)

측광학

Lv = fv / (Acosq) w = Iv / Acosq (lm/sr*m2=cd/m2=nit)

• luminance: luminous flux per unit solid angle per unit projected source area.

Luminance

n

dA

L

dIq

2

cos cos

cos

p

p

dd

d dIdL

d dA dA dA

dA dA

f

f w

w q q

q

Typical luminance values

sourceluminance level

(candelas/square meter)

Sun 1,550,000,000

Moon 2,500

Candle 10,000

60-W incandescent lamp 12,000

40-W fluorescent lamp 8,200

Zenith sky 1,100

Snow in sunlight 31,000

500-W tungsten filament 11,600,000

High pressure mercury arc 1,600,000

Typical Luminance Values

[Illuminating Engineering] (J. B. Murdoch, 2nd ed.)

The Inverse Square Law

• The illuminance is proportional to the intensity and inversely proportional to the square of the distance from the source. • The total luminous flux from a point source (intensity = I) is f = 4I. The area

of a sphere of which the center is coincident with the point source and the radius is d is A=4d2. Therefore, the illuminance on the inner surface of the sphere is E= 4I/4d2 = I/d2.

2 2/ /E I d LS d L


d

b

2

cosIE

d

b



Point Source Approximation

“five times rule”: the distance to a light source should be greater than five times the largest dimension of the source at which the error is ~ 1% compared to the prediction from the inverse square law.


General Inverse Square Law


2

'cosIdAd Id

d

bw

2

cos

'

d IE

dA d

b

2 2

cos cos cosdI L dAdE

d d

b b

for a point source;

for an element of an area source;

2

cos

cos cos

S

S

I L dA

L dAE

d

b

assumed to have a luminance L in the direction of point P

d is large enough compared to the dimension of the source.

[코사인 제 3 법칙 (cosine-third law)]

• 점광원에서 방출된 빛이 표면과의 수직 방향에 대해 q의 각도를 이루며 입사할 경우,

( )2 2' 3 2cos / cos / / cos cos /E I d I d I dq q q q

Example

2 m

3 m

b

a flat circular lamp 15 cm in diameter15 cm

a table

illuminance?

intensity?


Polar Plot of Luminance

The polar plot of angular distribution of luminance contains all information about luminance distribution on an emitting surface.

A point on the polar plot indicates one particular viewing direction along which the luminance is measured.

The luminance value is normally expressed by a specific color.

Example of the Polar Plot

<edge-lit backlight>

Viewing-angle Characteristics of Emitting Surfaces

Angular distribution of luminance measured on a direct-lit BLU* Figures: G.J. Park, IDW’06 Digest, p.953 (2006)

side lobeTV용 직하형 BLU

Lambertian Surface

Lambertian surface has a constant luminance for any viewing angle, i.e. thesame apparent brightness to human eyes. Many diffuse surfaces are Lambertian such as the surface of white paper orthe emitting surface of the moon. The Lambertian surface has a simple relation between the luminance andluminous exitance.

luminance

(cd/m2)

viewing angle (o)

Lambertian distribution

0o



Lambert’s Cosine Law

( ) cosmI Iq q

q

L

q

Ap

q

I

( )( )

constantcos

mI I

LA A

qq

q

2 / 2

0 0

( ) cos sinA

A

I d LA d d LA

M LA

f q q q q

f

Example

an 8-cm square Lambertianflat light source with aluminance of 500 cd/m2

Luminous exitance?luminous flux?intensity?

EXPERIMENTAL SQUARE

FLUORESCENT LIGHT (GE, 1959)

q

Measurement: Luminous Flux I

2 / 2

0 0

( , ) ( , )sinI d d d I

q q q q [Illuminating Engineering] (J. B. Murdoch, 2nd ed.)

( ) ( )

( )( )

( )

( )

1 2

1 2

o

1 2o

1 2

180

0

2 sin

2 cos cos

ZC

ZC

d I d I d

I

I

I

q q

q q

q q

f q w q q q

q q q

q

q

Zonal lumens

<Gonio-photometer>

[IESNA Lighting Handbook] (IESNA, 9nd ed.)


Measurement Examples

double-axis Gonio-photometer

Measurement: Luminous Flux II

uniform reflectance r

<Ulbricht Sphere>

Luminance L

dA

2

2 2

cos

4Y

LdA LdAdE

d r

q

dA at point X Y

independent of the position of Y!

The indirect illuminance is uniform

throughout the sphere.

lumens

Total reflected lumens → illuminance due to reflected lumens

( )

( )

2

refl.

2

11

4 1r

E

rr r r

r

r

r

direct illuminance + indiredt illuminance

small shield

illuminancemeter


The sphere is calibrated bymeasuring a standard source whosetotal lumen output is known, andwhose spatial and spectral propertiesare similar to lamps being measured.

[IESNA Lighting Handbook] (IESNA, 9nd ed.)

From Wikipedia, the free encyclopedia

http://upload.wikimedia.org/wikipedia/en/9/93/Commercial_Integrating_Sphere.jpg

http://upload.wikimedia.org/wikipedia/en/9/93/Commercial_Integrating_Sphere.jpg

* 김일호(LMS), [BLU 광학특성평가] (인하대 OTEC)

Measurement Example

Measurement: Luminous Intensity


mm

beam candela 측정: representative of the candela at the peak intensity of the beam


[example]

total flux=0.1 lm

A: q=10o 4.2 cd

B: q=5o 16.7 cd

q



Measurement: Luminous Intensity

Common Photometric Quantities, Units, and Symbols

Symbol Name Unit Abbreviation

flux lumen lm

I luminous intensity

candela cd = lm/sr

L luminance nit (deprecated, “nit” is not approved for use anymore)

cd/m2

E illuminance lux lx = lm/m2

M luminous exitance

(do not use lux) lm/m2

vi. terminology for display - hallym.ac.kr · 2015-04-10 · •radiometry: a set of techniques for...

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