During the use procedure of LED light bead, the generated photon may occur to the loss of photon in the following condition when gives out light. If so, the luminous quantity of LED would be declined and finally the ray of light is unable to pass through chip and arrive in the external.
- The internal chip exists any structure defect or the material contains optical absorption.
- In the emergent surface, photon may suffer reflecting loss which is caused by the difference of refractive index.
- Since the angle of incidence is bigger than critical angle of total reflection, it may result in total reflection loss.
Due to the reasons mentioned above, nowadays, the luminous efficiency of majority of big power LED flood lighting is about 70% while the rest 30% is forced to convert into heat energy. This is the reason why LED light bulbs always need to be equipped in heat dissipation device. In any event, it is just a temporary expedient because heat dissipation device would make the weight of fixture soar.
Fortunately, with the high practiced LED production processes, in order to cut down unnecessary photon loss, manufacturers add some packaging adhesive in the surface of chip, whose refractive index is a little higher, aiming to enhance extraction efficiency. In addition, the other function of packaging adhesive is to protect chip be free from damage. At the moment, the most common used packaging adhesive is epoxy resin and silicone. Depending on the feature of high light transmittance, large refractive index, good heat stability and low hygroscopicity, silicone is superior to epoxy resin so that it is always applied to big power LED flood lighting packaging.
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