LIGHTING & ACOUSTICS

INTRODUCTION

• The simplest definition of light is “visually perceived radiant energy". “Visible” light is just a small segment of the electromagnetic spectrum— a broad range of radiant energy which also includes X-rays, ultraviolet and infrared energy, micro-waves and radio waves.

• As visually perceived radiant energy, light powers the mechanism of sight. It is light, reflected from objects to our eyes, that allows us to see.

• Of all our senses, sight is the most dominant, controlling and defining how people perceive the world. And yet it’s impossible to prove that any two people see a given object in exactly the same way.

• In fact, it often seems that visual perception—an individual’s response to light—is extremely subjective. This makes it difficult to define and measure specific attributes of light.

• Furthermore, changes in light can change people’s perceptions. • A dark alley, for example, provokes an entirely different reaction than one that is

brightly lit. Lighting, therefore, can have a profound effect on people’s emotions and how they respond to an environment.

LIGHTING & VISION• The sun, stars & electric lamps are visible to us because of the light they generate.

• Most of what we see, however, it is visible because of the light that is reflected from the surface of objects.

• Our ability to see well- that is, to discern shape, color and texture and to differentiate one object from another-is affected not oly by the amount of light available for illumination but also by the following factors:

• Brightness

• Contrast

• Glare

• Diffusion

• Color

BRIGHTNESS• Brightness is an attribute of visual perception in which a source appears to be

radiating or reflecting light.

• In other words, brightness is the perception elicited by the luminance of a visual target. This is a subjective attribute/property of an object being observed.

• brightness, in physics, the subjective visual sensation related to the intensity of light emanating from a surface or from a point source.

•Even though these objects may be uniformly illuminated, their surfaces differ in brightness according to their•Color•Value •Texture

•Ability to reflect light

• Harmonious distribution of brightness is important for sharpness of vision and sensitivity to contrast, contrast being relatively small differences in brightness.

• Setting the brightness too low can again cause strain, decrease the visual stimulation and therefore also work performance.

• Darker surfaces in the room can work against the harmonious distribution of brightness and can cause feelings of oppression and anxiety.

• Brightness = illumination x reflectance

Contrast in brightness aids perception of shape & form

CONTRAST• Contrast is the difference in luminance and/or color that makes an object (or its

representation in an image or display) distinguishable.

• In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view.

• The maximum contrastof an image is the contrast ratio or dynamic range.

• Contrast is also the difference between the color or shading of the printed material on a document and the background on which it is printed, for example in optical character recognition.

Surrounding area (3) should range from 1/5 to 5 times the brightness of the task area (1)

3:1 is the maximum recommended brightness ratio between the visual task area and its immediate background (2)

Contrast using colors

GLARE

• Glare is difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night. Because of this, some cars include mirrors with automatic anti-glare functions.

• Glare is caused by a significant ratio of luminance between the task (that which is being looked at) and the glare source. Factors such as the angle between the task and the glare source and eye adaptation have significant impacts on the experience of glare.

SOLUTIONS FOR GLARE

Locate light fixtures out of the direct glare zone

Reduce the brightness ratio btw the light source & its background

• Exterior window shading strategies to avoid glare

• Use well sheilded or baffled fixtures that minimize direct view of bulbs or lamps.

DIFFUSION

Light diffusion• Light diffusion (how light is spread) can significantly

decrease dazzle and glare from the different surfaces and objects in a room.

• The more diffusely and evenly the light is spread the better dazzle and glare are prevented.

• Light diffusion can be defined as the ratio of the diffused reflected light to the totally reflected light.

• 1. Reflection from a bright polished metal surface or a mirror.

• 2. Reflection from an ordinary painted surface causes glare at certain angles.

• 3. Diffused reflection from EcophonAkutex™ surfaces prevents glare and dazzle.

• Diffused illumination reduces contrast & shadows.

• Concentrated source of light, incandescent downlight, produces a directional light with little diffusion. This enhances the perception of shape, form surface texture.

• Diffused light is useful for general vision.

• Can be used to provide visual accents, brightness variation.

• Examples of diffused lighting used in interiors.

COLOR• Color and Light

We tend to think of objects as having fixed colors—an apple, for example, is red. • In reality, an object’s appearance results from the way it reflects the particular light

that is falling on it. • Under white light, the apple appears red because it tends to reflect light in the red

portion of the spectrum and absorb light of other wavelengths. • If a filter is used to remove red from the light source, the apple reflects very little light

and appears black. • The fact that the color makeup of light can change, means that shifts can occur in the

color appearance of objects illuminated by it.

• All Light Is Not the SameDirect sunlight at noontime is an almost perfectly balanced light source—it contains all colors in nearly equal quantities.

• But daylight does experience color shifts. The colorappearance of objects changes dramatically in early morning or in the shade.

• Electric light sources can also exhibit variations in colormakeup. Incandescent lamps tend to produce more red and yellow light than green and blue, and appear to be “warm” in color.

• Because of the way incandescent light is produced, little can be done to manipulate its color characteristics.

• With fluorescent and high intensity discharge lighting, this latest technology makes it possible to manipulate the colormakeup of a given light source.

• White Light and Bright ColorsGenerally speaking, whiter light (comprised of equal amounts of all colors) makes colors appear more natural and vibrant.

• However, some portions of the spectrum are more important to a light’s colormakeup than others. Red, blue and green—the primary colors of light—can be combined to create almost any other color.

• This suggests that a light source containing balanced quantities of red, blue and green light can provide excellent color appearance even if this light source is deficient in other colors in the spectrum.

DAYLIGHTING

• The source of all daylight is the sun. its light is intense but will vary with the time of the day, from season to season and from place to place, it can also be diffused by the cloud cover, haze, precipitation or any pollution that may be present in the air.

• Daylighting is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides effective internal lighting.

• Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy use.

• Artificial lighting energy use can be reduced by simply installing fewer electric lights because daylight is present, or by dimming/switching electric lights automatically in response to the presence of daylight, a process known as daylight harvesting

High window openings allow daylight to penetrate more deeply into an interior space.

Locating window adjacent to perpendicular wall maximizes light entering.

DAYLIGHTING EXAMPLES• Bidirectional lighting – lighting from 2 directions raises

the level of diffused light in a space and reduces posssibilty of glare.

• Provision of skylights

Tubular skylights

Flat & domes skylights