Hi Actually it doesn't hurt your retina, it damages your cornea. This frequency of uv doesn't penetrate very far into the eye. This means that extra care is needed since it isn't just a matter of looking at the light. Any direct path from the lamp to the surface of your eye can cause damage. Most reflected uv light is attenuated quite a bit and is not as dangerous but one should still design their box to avoid reflective surfaces like aluminum. Even though 90% or so is lost, these lights are intense. Cardboard or conductive foam has about 0% reflections. One can get an idea of the reflected quantity by placing a piece of 'T'shirt near. It will glow if hit by the uv. Dwight