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Characteristics of LED 2018-03-27T20:41:00+00:00

Characteristics of LED

LEDs are solid-state devices. The advantages are:

1) Light Generated by LED is Directional

A. LED is all forward directional lighting, not Omni as conventional light bulb.
B. In general, beam angel is around 140 degree.
C. Utilize this directional characteristics and employee optical lens can achieve different light patterns.

2) LED can Generate Different Light Color

A. Wavelength determinate light color output: red, green, blue, yellow, or purple.
B. RGB light mix or different phosphor mix will create white light.

3) Temperature will Affect LED Efficacy

A. LED itself will generate heat, which will affect efficacy as well as LED life.
B. In general, 10 Degree increase will reduce 5 – 7% lumen output
C. Maintain P-N Junction temperature under 75 degree will enable LED last for over 50,000 hours.

4) Low Energy Consumption

A. 100 lm/W is commercialized, while over 200lm/W is achieved in lab.
B. ILess than 1/5 to 1/10 power consumption of conventional lighting is achieving or 80% to 90% of energy will be saved.

5) Long Life

A. No fragile parts, as conventional light bulb, to be broken.
B. Light will decay lumen output, but rarely burn out or dead.
C. A well-designed luminaire expects over 70% lumen maintenance at 50,000 hours usage.

LED Degradation and Failure: Junction temperature is the key parameter

Being solid-state devices, LEDs rarely burn out. Instead, the gradual degradation of light output, i.e. lumen depreciation, becomes the dominant failure mode of LEDs. The speed of lumen depreciation is closely relevant with the device’s “junction temperature”, which represents the temperature of the point where an individual diode connects to its substrate. Lower junction temperature leads to higher light output and slower lumen depreciation. Therefore, junction temperature is the key parameter for evaluating LED products’ life span.

The level of junction temperature is predominated by three factors, including drive current, thermal dissipation path and ambient temperature. In general, the higher the drive current, the greater the heat generated at the diode. As high-power LEDs are developed for general illumination application, the effectiveness of heat removal achieved by heat sink design becomes crucial in maintaining light output, life expectance and optical color.

To compare the durability of LEDs quantitatively, it is commonly referred to lumen maintenance, which represents how a lamp maintains its light output over its lifetime.LED products’ life span.

The level of junction temperature is predominated by three factors, including drive current, thermal dissipation path and ambient temperature. In general, the higher the drive current, the greater the heat generated at the diode. As high-power LEDs are developed for general illumination application, the effectiveness of heat removal achieved by heat sink design becomes crucial in maintaining light output, life expectance and optical color.