Basic Lighting Definitions
Lumen (lm): It is a unit of luminous flux & 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 & measures the luminous flux per unit area. Each application has its standard lux requirements. The task oriented areas like kitchen or sewing will require the high lux values compared to non task areas like corridor or lobbies.
Correlated Color Temperature (K): It is method of describing the color characteristics of light, usually either warm (yellowish), neutral (off white) or cool (white), and measuring it in degrees of Kelvin (°K).
Color Rendering Index (CRI): It is the ability of light source to produce the natural colours. For example an object seen in sunlight will show the natural colours (high CRI) whereas show different color 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 a concentrated light which is better for accent lighting. A wide beam gives a more general, softer light suitable for ambience lighting applications.
What is LED Lighting?
LED stands for Light Emitting Diode. It emits light when current passes through it.
What are the benefits of LED Lighting?
LEDs have numerous benefits over conventional lighting technologies –
a. Saves upto 50% energy over CFLs
b. Have long life of 50000 hrs
c. Do not emit UV and IR radiations
d. Do not contain mercury
e. Can produce millions of color options
How LEDs life is defined?
Unlike conventional lamps that fail abruptly, LEDs depreciates slowly over time. The life of LED is defined as when its lumen output depreciates to 70%.
How is the life of LEDs compared to conventional lamps?
GLS : 1000 hr
Halogen : 2000 hr
CFL : 5000 hr
FTL : 6000 hr
LED : 50000 hr
What is the physical significance of 50000 hrs life?
4 hr daily operation : 34 yrs
8 hr daily operation : 17 yrs
12 hr daily operation : 11 yrs
24 hr daily operation : 05 yrs
What are the challenges with LED Lighting?
LEDs are very sensitive to temperature & also produce a lot of heat during operation. This heat should be removed from system to maintain the junction temperature within prescribed limits.
LED are point sources so are prone to cause glare if the optics is not properly designed.
What is junction temperature?
It is the temperature of the PN junction in LED chip
What happens if the junction temperature increases?
An increase in junction temperature may drastically reduce LED performance like,
a. It reduces LED life
b. LED may change color
c. Lumen depreciates
d. LED forward voltage changes
What is the role of heat sink?
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.