why top downs ?

[Snaz]

Originally Posted by sphelps

Glass actually has a refraction index close to water it's about 1.4 compared to 1.3...

So if water has a comparable refractive index as glass then surely then refraction is not the issue here correct? My logic is that the glass just does not allow some of the light through.

Again lets look at the 3/8" glass cover on the face of a metal halide light, it blocks up to 80%? of the UV rays does it not? This to me illustrates clearly that glass has great potential to block light.