White LED

Light Emitting Diode or LED is one of the light sources. Basically, LED is diode which consists of two types semiconductor, those are n-type and p-type. These semiconductors are connected at a junction. As a diode, LED can be a conductor if forward current flow through the LED.  How can LED emit light??

Electrons are majority charge carrier at n-type semiconductor, while holes are majority charge carrier at p-type semiconductor. When forward voltage is applied to the LED holes and electrons are pushed to the junction, then they meet followed emitting light. This light depends on band gap energy between conductance and valence band.

Basically, LED can emit only one color, but now white LED which consist many colors has been introduced to be applied in technology such as monitor. Now, White LED has begun to replace incandescent lamp or fluorescent lamp as a lighting lamp. There are two primary ways to produce white LED, RGB system and Phosphor-based system.

In RGB System, three basic colors (Red, Green, and Blue) are mixed resulting white LED. The second way is similar with fluorescent lamp which use phosphor to create white light. How can Phosphor create white light??

Stokes Shift is the key how to produce white light in Phosphor based system. Light from junction could be blue light or UV light then the energy from this wavelength will be is absorbed by phosphor. Then phosphor emits the light with lower energy than it absorbs.

LED has many advantages compared with another light source such as incandescent and fluorescent. Long life, shock resistance, compact, high efficiency are the advantages. However, the problem that challenging now is how to maintain junction temperature. LED performance largely depends on the junction temperature. Increasing junction temperature will decrease LED performance. So that thermal management in LED is very important.