when is it possible to look trough a tank and when does it act like a mirror?

[JelleBijker]

Hi everyone,

i have a rather complicated question, hopefully someone here knows the answer.

i have noticed that if you have a rectangular reef tank (say a room divider) you can look trough the front glass, trough the water AND trough the back glass and see whats on the other side of your tank. (so far its pretty DUH...)

however: if you look trough the front glass and try looking trough the tank out the side glass that won't work. in this case the side glass works as a mirror.

so if the glass is paralel it is transparant and if the glass is at a 90 degree angle its a mirror.

my question is: at witch angle does the side glass start to act like a mirror in a reef aquarium?

ik really hope someone can help!

greetings
Jelle

 

[Turtlesteve]

Have a read here: https://en.wikipedia.org/wiki/Total_internal_reflection

Beyond this, every interface (glass to air and glass to water) will reflect a little bit due to the difference in refractive index.

Steve

Hi everyone,

i have a rather complicated question, hopefully someone here knows the answer.

i have noticed that if you have a rectangular reef tank (say a room divider) you can look trough the front glass, trough the water AND trough the back glass and see whats on the other side of your tank. (so far its pretty DUH...)

however: if you look trough the front glass and try looking trough the tank out the side glass that won't work. in this case the side glass works as a mirror.

so if the glass is paralel it is transparant and if the glass is at a 90 degree angle its a mirror.

my question is: at witch angle does the side glass start to act like a mirror in a reef aquarium?

ik really hope someone can help!

greetings
Jelle

 

[JelleBijker]

Thanks for the reply!

i was already aware of the theory behind my question, problem is that I am unable to do the calculations that are nessecary to get the final answer...:hmm4: for starters my math aint good enough, but I also don't know several of the material related values.

i was kinda hoping someone here has the knowledge to calculate it, or even better... someone who tried it with some kind of aquarium setup.

 

[nereefpat]

my question is: at witch angle does the side glass start to act like a mirror in a reef aquarium?

If you look through the front, at a side, the side will look like a mirror. If you look through the side, at the other side, it won't act as a mirror.

From your fishes' view in the tank, nothing will look mirrored.

Does that answer your question?

 

[JelleBijker]

sorry, that is nog the answer is was looking for.

glass on a 90 degree angle mirrors. does is also on 80 degree? and 70?

at wich angle does is stop acting as a mirror?

 

[nereefpat]

It depends on the refractive indices of each material. It looks like the answer is in the "Critical angle" section of the page [MENTION=7162]Turtlesteve[/MENTION] linked.

The page lists the critical angle of visible light from acrylic into air as 41.8 degrees.

Your answer is possibly: angle = arcsin (1.33(water refractive index)/1.5(air refractive index)

 

[Turtlesteve]

The critical angles for glass and acrylic are almost the same. It's arcsin(1/1.52) = 41.1 degrees for glass and arcsin(1/1.5) = 41.8 degrees for acrylic.
For a 90 degree corner it's almost impossible to look diagonally through the corner and see through it. If you had a corner near this critical angle (say 45 degrees), it would either mirror or not mirror depending on what angle you looked at it.