LEDs operate similarly to photovoltaic cells, except that the transfer of electrons is reversed of how photovoltaics generate electricity from solar energy. The p/n junction with a semiconductor is still at work here, where the “p” energy band has an abundance of electrons and the “n” energy band has an abundance of electron holes, or atoms without electrons in their electron shells.
When you connect power to an LED, the electrons in the “p” band get excited and jump the band gap, where they fill electron holes called the junction point. When they fill the junction point, they emit a photon, or unit of light. This is called electroluminescence, the foundational phenomenon behind how an LED functions. Electroluminescence is based upon the properties of the semiconductor in the LED. For instance, an early LED (that produced visible red light) used gallium arsenide. LEDs that produce different colors use different semiconductors—such is the case with white LEDs.
How to Get White Light from an LED
In the mid-90s, blue LEDs were invented from Professors Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura. Blue LEDs were difficult to invent because they required a specific semiconductor in order to emit photons in the proper wavelength for blue light--it turns out that Gallium Nitride was the secret ingredient needed for blue LEDs.
This invention was groundbreaking because producing white light from an LED was closer to reality. It finally became one when a phosphorus layer was applied to the LED lens. White light LEDs paved the way for developments into newer technologies such as clearer televisions, more efficient light bulbs, and, of course, LED light fixtures for solar street lights.
We’ve seen improvements since the invention of white LEDs primarily in efficiency and longevity. White light LEDs have seen exponential increases in efficiency because of what’s known as Haitz’s Law. This law outlines the cost of LEDs vs efficiency on a logarithmic scale, thus demonstrating how LEDs have grown in efficiency and dropped in price over time.
LED Standards for a Manufacturer
Color Temperature
White LEDs are the result of a phosphorus layer on top of a UV-emitting diode, but the phosphorus layer often determines the color temperature of the light. A common color temperature for LEDs is 4,000K, or a “cool white,” but this can be adjusted based on the needs for the client.
