Evolution of light by human being dates back to incandescent light. Today, LED technology has proved to be the most efficient system. A light-emitting diode (LED) is a semiconductor (electrical) device, that restricts current flow in one direction. Semiconductor diodes are comprised of two regions, one is p region (positive charges) and other is n region (negative charges). When voltage is applied, the electrons move across the n region into the p region. During the process of an electron moving through the p-n junction, it releases energy. The dispersion of this energy produces visible light.

LED Lighting can come in many different colours, the most common of these in household usage lights are Warm White, Neutral White and Cool White. Lighting colours Warm White with a Kelvin rating of 2700K-3300K, Neutral White with a Kelvin ranging from 5500K-6000K, Cool White with a Kelvin rating of 6000K-6500K.

CRI is a measurement technique, to define how well a given object displays the true colours of an object. The general colour rendering index rates colour rendering out of 100(100 being the sunlight). The higher the index, the better the colour rendering and different light sources have different colour rendering characteristics.

CRI <70    CRI >90

Colour temperature of a light source is the temperature of an ideal black-body radiator (solid object with certain properties heated up to point of incandescence) that radiates light of comparable due to that of the light source, and its temperature is expressed in Kelvins. For colours based on black body theory, blue occurs at higher temperatures, while red occurs at lower temperatures. This is the opposite of the cultural associations attributed to colours, in which 'red' is 'hot', and 'blue' is 'cold'.

High Efficacy

Efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI). Latest lab data showed efficacy more than 250 lm/W. However, in real lighting fixture we must consider several factors such as control gear performance, luminous flux depreciation with increasing junction temperature, optical losses etc., which reduce the overall system efficacy.

“Efficacy increase over the time for various light sources.”

Environmental Impact

Using LEDs reduce environmental impact in several areas. Longer lamp life means that fewer resources are required for maintenance. They also use no mercury and less phosphorus than fluorescent alternatives. These facts combined with high efficiency make LEDs a smart choice while reducing the footprint on the nature.

Controllability

LEDs can be integrated into the electronic control system which allows for control of color balance and intensity, independent of each other while maintaining color rendering accuracy. This is impossible with traditional light sources. For general illumination, LEDs can dim from 0.1 % to 100 %.

Durability

LEDs are highly rugged. They incorporated no filament or fragile glass bulb that can be damaged due to mechanical vibrations and shocks. LED light fixtures are especially appropriate in applications with strong probability of lamp breakage such as bridges, industrial areas, or stadiums.

Low-temperature operation

Low temperatures present a challenge for fluorescent lamps. At low temperatures, higher voltage is required to start fluorescent lamp, and luminous flux is decreased. In contrast, LED performance is inherently increased at low operating temperatures. This feature predestines LEDs for grocery stores, cold storage facilities, and outdoor application.

No UV emissions/ Health aspects

LEDs emit light with negligible ultraviolet (UV) and very little infrared radiation. Small amount of radiated heat by LEDs makes them appropriate for goods which are sensitive to heat. The lack of UV radiation (with appropriate design of optical part) makes them an attractive also for illumination of delicate objects such as artworks as well as materials subject to UV degradation.

LED vs Other Sources of Light

Incandescent or fluorescent bulb emits light and heat in all directions. For direct lighting applications LED lighting uses both light and energy more efficiently. For example, an incandescent or compact fluorescent (CFL) bulb inside of a recessed can will waste about half of the light that it produces, while a recessed down light with LEDs only produces light where it's needed.

Lamp Type	Incandescent buld	Halogen lamp	Metal halide lamp	Mercury vapor lamp	LED
Efficacy (lm/W)	6-16	16-30	75-125	40-75	80-160
Input power: (W)	20-60	55-100	20-24000	50-500	0.2-100
Hazardous chemical content:	no	Halogens	Argon, Mercury	Argon, Mercury	no
Electronics ballast:	no	In general no	needed to control the current	needed	needed
CRI:	100	100	70-95	40-60	65-97
Application:	Indoor, outdoor	Indoor applications like shops, residential	Floodlight, outdoor, shops	Outdoor applications, streetlights, facade	Indoor, Outdoor
Additional Information:	high IR radiation	high IR radiation	High UV radiation	High light pollution	little UV and IR radiation
Lifetime : (hours)	1000	1000-3000	6000-20000	4000	50000
CCT	2700	2700-3500	3800-7000	3200-4200	2700-8000
Dimmable	yes 0-100%	yes 0-100%	yes 50-100%	no	yes 0.1-100%

Way back in 1960s, a bulb was measured by its ‘candle power’. One would ask for a 40-candle bulb and be sure to get light equal to 40 candles. Over the years, the smart businessman changed it quietly to 40 Watts. The common man never realised the smooth transition to this word “watt”, and assumed 40 watts was equal to 40 candles. No. It is not. 40 watts consumes 40 watts power, but doesn’t deliver 40 candles of light.

Therefore, it is imperative for us to know the worth of light for the watts burned by bulb. The measure of light is called Lumens.

Lumens measure how much light you are getting from a bulb. More lumens mean it's a brighter light; fewer lumens means it's a dimmer light.

• Lumens are to light
• Pounds are to bananas
• Gallons are to milk

Lumens let you buy the amount of light you want. So, when buying your new bulbs, think lumens, not watts.

The brightness, or lumen levels, of the lights in your home may vary widely, so here's a rule of thumb:

To replace a 100-watt incandescent bulb, look for a bulb that gives you about 1600 lumens. If you want something dimmer, go for less lumens; if you prefer brighter light, look for more lumens.

Replace a 75W bulb with an LED bulb that gives you about 1100 lumens
Replace a 60W bulb with an LED bulb that gives you about 800 lumens
Replace a 40W bulb with an LED bulb that gives you about 450 lumens