why top downs ?

[sphelps]

Originally Posted by Snaz

So if water has a comparable refractive index as glass then surely the 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.

Glass can filter UV but this would also be irrelevant since UV is not visible to us and therefore doesn't greatly effect how we see things. Glass will block/absorb light, but so does water which is why light intensity is less with more water depth. You should also note that the glass used in MH fixtures has a coating or specific formula to lower the emissivity which results in the high reflection of UV light, this is not typical with standard glass.

The point is the glass has little to no effect on the topic here. If you could remove the glass from your aquarium you would still see the same effect comparing top to side views (other than a little less green tint from the sides). Acrylic has no tint and the index of refraction is even closer to water and yet these tanks still suffer from side perspective. For this reason I don't see glass as part of the equation, if a variable can be removed without effecting the outcome then it is not part of the problem.

[fishytime]

So, why then do clams also look different through the glass then they do top down?.....I have one crocea that looks purple through the glass but is green top down.

[o.c.d.]

Iridophores have groups of cells that contain reflective platelets which act as light intensifiers. Depending on the orientation of the platelets, relative to incoming light, They can defect the light away or towards the clams eyes. That is also how the clam can react to a shadow of a hand passing over,or the difference of appearance form viewing at different angles.