ARC 252 : Lighting & Acoustical Design Department of Architecture I BRAC University 1ARC 252 : Lighting & Acoustical Design LED

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LED Light Emitting Diodes ARC 252 : Lighting & Acoustical Design3

4 What is LED lighting? A Light Emitting Diode (LED) is a semiconductor device, which converts electricity into light. LED lighting has been around since the 1960s, but is just now beginning to appear in the residential or industrial market for space lighting. At first white LEDs were only possible by “rainbow” groups of three LEDs - red, green, and blue - by controlling the current to each to yield an overall white light.

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8 LIGHT TYPELIFE TIME Incandescent3k Halogen10k T12 fluorescent20k Metal halide5k-15k T8 fluorescent20k Best-in-Class Power LED>60k High-pressure sodium20-24k T5 fluorescent20k Low-pressure sodium18k LIGHT Source Comparison

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10 LEDs are produced in a variety of shapes and sizes. The color of the plastic lens is often the same as the actual color of light emitted. purple plastic is often used for infrared LEDs. most blue devices have colourless housings. Modern high power LEDs such as those used for lighting and backlighting are generally found in surface-mount technology LED Types

ARC 252 : Lighting & Acoustical Design11 Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world. They do dozens of different jobs and are found in all kinds of devices. Among other things, they form numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. Collected together, they can form images on a jumbo television screen or illuminate a traffic light. How LED Works

ARC 252 : Lighting & Acoustical Design12 Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescent bulbs, they don't have a filament that will burn out, and they don't get especially hot. They are illuminated solely by the movement of electrons in a semiconductor material, and they last just as long as a standard transistor. The lifespan of an LED surpasses the short life of an incandescent bulb by thousands of hours. Tiny LEDs are already replacing the tubes that light up LCD HDTVs to make dramatically thinner televisions.

LED ARC 252 : Lighting & Acoustical Design13 Advantages

ARC 252 : Lighting & Acoustical Design14 LEDs are better at placing light in a single direction than incandescent or fluorescent bulbs. Because of their directional output, they have unique design features that can be exploited by clever designs. Water-/ gas-proof (IP67 & 68), outdoor fixtures (buildings, street lighting, expressways) are also available.

ARC 252 : Lighting & Acoustical Design15 LED lights are more rugged and damage-resistant than (compact) fluorescent and incandescent bulbs. LED lights do not flicker. They are very heat sensitive; excessive heat or inappropriate applications dramatically reduce both light output and lifetime. LED lighting can be dimmed.

ARC 252 : Lighting & Acoustical Design16 Typically, a LED-based light bulb uses 10% of traditional and only 50% of energy-saving lighting technologies. It produces almost no heat (e.g. savings on air conditioning). Lifetime is in the order of 50’000 hours (even up to 100’000 hours). Tremendous energy savings up to 90%. Over a lifetime, fewer light bulbs need to be used. Energy Savings

ARC 252 : Lighting & Acoustical Design17 LED light bulbs do not contain any hazardous materials and therefore do not generate any hazardous waste. LED light bulbs can be recycled. LED light bulbs do not flicker, do not cause RF interference, are much easier on the eyes, and its ‘light temperature’ makes you feel much more comfortable. Environmental Considerations

ARC 252 : Lighting & Acoustical Design18 Initial higher purchasing costs are easily returned within three years! Electricity cost savings in the order of 40 to 95% are realistic. New constructions: Cost savings (e.g. installation, cabling, transformers, ballast, and interior design) are in the order of 20-30%. Investment Considerations

COLOR Rendering ARC 252 : Lighting & Acoustical Design19

ARC 252 : Lighting & Acoustical Design20 Although light sources may have the same color appearance, this doesn’t necessarily mean that colored surfaces will look the same under them. Two lights that appear the same white, may be the result of different blends of wavelengths.

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And since the surface may not reflect the constituent wavelengths by the same extent, its color appearance will change when it is exposed to one or other light. A piece of red cloth will appear ‘true’ red when seen illuminated by white light produced by a continuous spectrum, but in an equally white looking mixture of yellow and blue light it will look greyish brown. Because of the absence of red wavelengths, there is no red for the cloth to reflect into the eye to notice. ARC 252 : Lighting & Acoustical Design22 Color Rendering

ARC 252 : Lighting & Acoustical Design23 is an important criterion when selecting light sources for lighting application solutions. To classify light sources on their color rendering properties the so called color rendering index (CRI or also denoted as Ra) has been introduced. The scale of the Ra ranges from The following table shows the meaning of the Ra values: Ra = Excellent color rendering properties Ra = Good color rendering properties Ra = Moderate color rendering properties Ra < 60 Poor color rendering Color Rendering

Color Temperature ARC 252 : Lighting & Acoustical Design24 Although white light is a mixture of colours, not all whites are the same since they depend on their constituent colours. So a white with a higher proportion of red will appear warmer and a white with a higher proportion of blue will appear cooler. In order to classify the different types of white light, the concept of colour temperature is applied which is described as the colour impression of a perfect black- body radiator at certain temperatures.

This concept can be best explained with the help of familiar thermal radiators like the filament of an incandescent lamp or an iron bar. When these materials are heated to a temperature of 1000 K their colour appearance will be red, K they will look yellow white, 4000 K neutral white, and K cool white. In other words: the higher the colour temperature, the cooler the impression of the white light becomes. ARC 252 : Lighting & Acoustical Design25 Color Temperature

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