There are some key points in designing of photonic crystal LED street lights, one of which is period. Period is related with the diffraction distance. The smaller the period, the longer the diffraction distance. Therefore, it is needed for designers to find a suitable period.
Another key point is height. Height has closed relation with diffraction efficiency. As a matter of fact, not all light will be impacted by diffraction. Light affected related with the generation of diffraction efficiency. During the process of creating photonic crystal LED, scientists need to take some highly accurate calculation to find out the final G value (optimal value).
How to calculate the total light usage on the surface of LEDs? FDTD is a typically used mathematical method to do this job for photonic crystals. Non-photonic crystal LED flood light has relatively smooth surfaces. After sending out light, rays generated by lighting sources in contact with the air will be totally reflected back by the surface.
However, photonic crystal LED can keep light from totally reflection and “reflect” light outwards. From the distribution curve (in a certain height) we can find that when period get to 1.5um, the light efficiency can reach up to its crest value. However, the maximum value of light efficiency is around 2.5um. Thus we can deduce that this space have a very long period but a very low height. It is suggest that the producing of photonic crystals is rather simple: finding out the most suitable period 1.5um, longer than wavelength. Most existing photonic crystal LED lights can meet this period and consequently have a high efficiency. This kind of photonic crystal is also named period photonic crystals.
There are several technical methods to create photonic crystals. The current temporary used is EB. In the mass production and commercialization, designers usually chose to use another method which costs much less. Theoretically, the calculated light efficiency of photonic crystal LED should be 3 times higher than normal LED. But in practices, this value is only 50% higher. These errors mainly generated during the process of structure design: inappropriate period setting. Besides, the tiny cracks in chips may also reduce the light efficiency of photonic crystal LEDs. Every steps in the production process is rather important.