3. Electrons in the edge of p-type section. Electrons pass LED PN junction and finally reach the edge of p-type section. Most of them will be captured by the large amount of holes within p-type section. Since electrons have higher potential energy than holes, after being captured by holes, this potential energy will be released as the form of electromagnetic wave (LED Street Light). The light color all depends on the material of diodes. Different diodes has different band gap (different potential energy), which can emit lights with different wavelengths. As we all know, wavelength determines the color of the light. Wavelength within visible range can be seen by human eyes. Electrons from n-type section originally have a higher potential energy than holes within p-type section. In addition that electrons’ potential energy is raised when they pass though the space charge region. It is quite easily for them to reach up to the band gap potential energy. Notice that, this potential energy gained by electrons has nothing to do with external electric field, only decided by LED Projects materials used in n-type region and p-type region.
4. Electrons within p-type section. Most electrons will be combined by holes when they enter p-type region. This process will cause the reduction of holes in the edge of p-type region. Since we add a forward bias voltage on LED PN junction, this reduction can be immediately supplemented by holes given by the positive potential connected to the other side of p-type region. External electric field exerts a forward force on electrons and make them accelerate, collide with nucleus and other electrons within p-type region. During this process, energy created by external electric field is converted into heat energy.
According to the above analysis we can see that the light energy generated by electron-hole combination is not decided by external electric field by materials used in p-type section and n-type section. It is a fixed characteristic of LED PN junction. On the other hand, all of heat energy created by PN junction is a conversion of electric energy from external electric field. It is an inevitable outcome of LED. Thus a good cooling system is very important for LED lighting applications, especially for those LED lamps with high power consumptions. For the reason that LED cannot work in high temperatures.