UV-light is a very useful tool to inspect the quality of hatching eggs. Exposure of (hatching) eggs to UV-light (preferably with a wave length of 365 Nm, and preferably combined with a black light filter) reveals contamination of the shell which cannot be observed in normal day light. When the eggs are lighted with a UV lamp any organic material on the shell shows very clearly, also after washing or brushing the eggs to take the dirt off. Also urates show very clearly on the shell under UV-light. When the light is directed to the point of the egg it can also be checked if the eggs are washed, as the washing water will dry up at that point and will show a clear stain. 

UV-light typically has a wave length between 100 and 400 Nm (wave lengths between 10 and 100 Nm are called extreme UV). Not all wave lengths are equally effective for the inspection of egg shells. Optimal wave length is approximately 365 Nm, which is in the range of the so-called UV-A. UV-B and UV-C lights are much less effective.