why top downs ?

[Snaz]

I would agree that corals are more pigmented where the "sunlight" hits them but a glass interface reduces the amount of light through.

Imagine looking at penny top down through one foot of water. Then imagine looking at the same penny through one foot of glass. The penny under the glass would look dull compared to the water penny.

[sphelps]

Originally Posted by Snaz

I would agree that corals are more pigmented where the "sunlight" hits them but a glass interface reduces the amount of light through.

Imagine looking at penny top down through one foot of water. Then imagine looking at the same penny through one foot of glass. The penny under the glass would look dull compared to the water penny.

Interesting logic but I'm not sure who's tank was 12" thick glass or who even has a piece of glass like that lying around to try such an experiment Glass actually has a refraction index close to water it's about 1.4 compared to 1.3, so given that tanks are generally built with thin glass when compared to the amount of water you're looking through the effects are not that relative. Try looking through glass from top down, which is often done for photography, you won't see a real noticeable difference.

The fact is, like already said, everything looks brighter and more vivid because you're looking parallel to the light source. Our vision is based on how light reflects back to our eyes and parts in direct light look brighter while other parts not in direct light are more shaded and dull. Look around outside as some stationary objects when the sun is low in the morning and when it is high in the afternoon.

[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.

[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.

[Myka]

Originally Posted by Snaz

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.

Take a look at Sanjay's lighting pages. Several of the DE bulbs give PPFD numbers with glass, and without glass. There is very little difference. The glass does not block very much of the light.