Generic FAQs on Lighting

Lumen (lm): It is a unit of luminous flux and a measure of the total amount of visible light emitted by a source.

Efficacy (lm/W): It is a measure of how efficiently a lighting source produces visible light per unit of input wattage. LEDs have high efficacy >150 lm/W compared to GLS 10 lm/W or CFL 60 lm/W.

Lux (lm/m²): It is the unit of illuminance and measures the luminous flux per unit area. Each application has its standard lux requirements. The task-oriented areas like kitchens or sewing will require high lux values compared to non-task areas like corridors or lobbies.

Correlated Colour Temperature (K): It is a method of describing the colour characteristics of light, usually either warm (yellowish), neutral (off-white) or cool (white), and measuring it in degrees of Kelvin (°K).

Colour Rendering Index (CRI): It is the ability of a light source to produce natural colours. For example, an object seen in sunlight will show the natural colours (high CRI), whereas it will show different colour if seen under blue or green light (low CRI).

Beam Angle: It indicates the spread of light from the light source. A narrow beam gives concentrated light, which is better for accent lighting. A wide beam gives a more general, softer light suitable for ambience lighting applications.

LED stands for Light Emitting Diode. It emits light when current passes through it.

LEDs have numerous benefits over conventional lighting technologies –

a. Saves up to 50% energy over CFLs
b. Have long life of 50,000 hrs
c. Do not emit UV and IR radiations
d. Do not contain mercury
e. Can produce millions of colour options

Unlike conventional lamps that fail abruptly, LEDs depreciate slowly over time. The life of an LED is defined as when its lumen output depreciates to 70%.

GLS: 1,000 hr

Halogen: 2,000 hr

CFL: 5,000 hr

FTL: 6,000 hr

LED: 50,000 hr

4 hr daily operation: 34 yrs

8 hr daily operation: 17 yrs

12 hr daily operation: 11 yrs

24 hr daily operation: 5 yrs

LEDs are very sensitive to temperature and also produce a lot of heat during operation. This heat should be removed from the system to maintain the junction temperature within prescribed limits. LEDs are point sources, so are prone to cause glare if the optics is not properly designed.

It is the temperature of the PN junction in the LED chip.

An increase in junction temperature may drastically reduce LED performance, like:

a. It reduces LED life

b. LED may change colour

c. Lumen depreciates

d. LED forward voltage changes

Heat sink is required to dissipated heat generated by LEDs during operation. Since ambient temperature in India varies from – 5 0C to + 55 0C so the heat sink design should ensure effective thermal management under all circumstances. It should be made of high grade aluminum & should have no pores (like in gravity die cast heat sinks) providing resistance to heat flow. Garnet uses aluminum pressure die cast or extrusion heat sinks.