Effects of various aquarium covers on light transmission

[Dana Riddle]

I got a private message from GaryE and thought my reply might be of interest to others. Here’s the message:
I know you have done innumerable studies on the various different lighting packages available. Have you ever studied the effects of different coverings on PAR levels?

Specifically, I'm interested in the difference between glass top vs egg crate vs mesh type screens.

I started my tank with the standard glass tops that came with it and decided that I wanted to go to something more open, so I went open top for a while. I had a very nice little hawk go carpet surfing, so that was a bad option. I have since moved to egg crate (white plastic) and am not real excited about the amount of loss I can perceive. Just to the naked eye it seems to be quite a bit of drop in light level. Whether this is just a loss of spread or actual loss of PAR I don't know as I don't have a par meter to check.


Thoughts?
My reply:
This took a bit of lab work using an Apogee MQ-510 quantum meter and a ‘globe’ Cree 6500K LED as the light source.
Eggcrate material: There is ‘good’ eggcrate and ‘cheap’ eggcrate. Good eggcrate has a ‘thick’ side and a ‘thin’ side – this acts as a parabolic lens and can concentrate light. I wrote an article about this for FAMA in the late 90’s and found if that orientation could focus point source light as much as 25% - of course, there is a reduction in light outside of the focus area. I do not have ‘good’ eggcrate anymore - the stuff being sold in big box stores is the ‘cheap’ stuff. However, if you’re fortunate to have quality eggcrate – and if memory serves – light will be focused if the thick side is up.
I have only ‘cheap’ eggcrate, but found there is a difference between white and black material
Black eggcrate reduced light intensity by 20%, while the white by only 12%.
Glass: I used a glass cover made for an aquarium, maybe 1/8” to 3/16”. Light intensity was reduced by 12%. Bear in mind glass will often transmit ultraviolet radiation. Not much of an issue if you’re using LEDs, but could be if you’re using a metal halide lamp.
Acrylic (thin and thick pieces): Light reduced by 12%. Acrylic will absorb UV and will eventually yellow and possibly disintegrate (if it is thin.)
Fiberglass window screen material: Reduced light by 44%.

 

[ScottR]

I’ve always wondered this as well. Nice to read this write up.

 

[User1]

Thanks @Dana Riddle .

I know it is frowned upon but it is why I keep an open top. I do a safety or newcomers briefing for each new fish upon arrival. Anyway I explain how tall the tank is and that there is no safety net should they get coached into playing flipper or doing any Parkour.

On a serious note - always assumed there was be a loss just didn't know how much. Also didn't know about cheap vs quality egg crate. Learned something new today.

 

[gabrieltackitt]

I got a private message from GaryE and thought my reply might be of interest to others. Here’s the message:
I know you have done innumerable studies on the various different lighting packages available. Have you ever studied the effects of different coverings on PAR levels?

Specifically, I'm interested in the difference between glass top vs egg crate vs mesh type screens.

I started my tank with the standard glass tops that came with it and decided that I wanted to go to something more open, so I went open top for a while. I had a very nice little hawk go carpet surfing, so that was a bad option. I have since moved to egg crate (white plastic) and am not real excited about the amount of loss I can perceive. Just to the naked eye it seems to be quite a bit of drop in light level. Whether this is just a loss of spread or actual loss of PAR I don't know as I don't have a par meter to check.


Thoughts?
My reply:
This took a bit of lab work using an Apogee MQ-510 quantum meter and a ‘globe’ Cree 6500K LED as the light source.
Eggcrate material: There is ‘good’ eggcrate and ‘cheap’ eggcrate. Good eggcrate has a ‘thick’ side and a ‘thin’ side – this acts as a parabolic lens and can concentrate light. I wrote an article about this for FAMA in the late 90’s and found if that orientation could focus point source light as much as 25% - of course, there is a reduction in light outside of the focus area. I do not have ‘good’ eggcrate anymore - the stuff being sold in big box stores is the ‘cheap’ stuff. However, if you’re fortunate to have quality eggcrate – and if memory serves – light will be focused if the thick side is up.
I have only ‘cheap’ eggcrate, but found there is a difference between white and black material
Black eggcrate reduced light intensity by 20%, while the white by only 12%.
Glass: I used a glass cover made for an aquarium, maybe 1/8” to 3/16”. Light intensity was reduced by 12%. Bear in mind glass will often transmit ultraviolet radiation. Not much of an issue if you’re using LEDs, but could be if you’re using a metal halide lamp.
Acrylic (thin and thick pieces): Light reduced by 12%. Acrylic will absorb UV and will eventually yellow and possibly disintegrate (if it is thin.)
Fiberglass window screen material: Reduced light by 44%.

Window screen reduced by 44%?!? That’s crazy!

 

[User1]

I wonder, and not for more testing, but the effects of standard layout panel vs. narrow puck style vs. lens. I know with the a360x from Kessil the spread is 130 degrees but adding the lens narrows it and increases par by more focus / direction.

Not sure what effect, if any, it would have to help or not. I guess the loss is the light being blocked so probably doesn't matter.

 

[swiss1939]

Egg crate is standard material used in film/tv lighting to reduce the spread of lighting fixtures. This means you are getting more parallel light beam, but will definitely reduce a.) total intensity, b.) how far of a spread a single fixture can provide that intensity. So if you are using egg crate you might need to use multiple fixtures to make up for lost spread. Egg crate works fine for broad lighting fixtures that cover the whole area trying to be blasted with light, while preventing that light from spreading beyond the intended target.

This effect is exponentially related to the distance away from center of the lighting source. So yeah you get 12% reduced par on the egg crate, but its less so directly below the light source and way more so the further away from center you get from the light sources aimed target. Using the par chart from Bulk Reef, you can see for 6" depth a single reefled90 is about 312 par in the center directly below the light and 165 at the outer edge of the tank. With an egg crate you would expect probably 265-300 par in the center and probably closer to 40-50 par at the outer edge. This is because the egg crate is sitting 6" below the light source, so the narrowing effect is increased as if you were to draw a direct line from the center of the light source to the egg crate, you would see the light is basically being blocked by the egg crate at the outer edges of the tank. This is because most of the light at that distance from center is not travelling parallel to the egg crate slats. This means that at 18" depth you are probably getting almost no par at the outer edge with a single light source in a 24" wide tank. If the egg crate was literally up against the light fixture, then you've got a more even par distribution loss because the angle of the light coming from the center of the source is much more parallel when it reaches the egg crate slats, but then your egg crate would no longer serve its purpose of preventing fish from jumping!

I can imagine using window screen would absolutely reduce the intensity the most because it is much finer holes which means you are getting more material covering the same space compared to egg crate.

I'm curious how the red sea diy screen kit affects lighting as its much less fine grain and is sort of clear plastic. I haven't put mine together yet to test it.

 

[GaryE]

Thanks for the write up Dana. This helps a lot. I may have to look into a different method to keep the critters in the tank.

 

[Dana Riddle]

Thanks @Dana Riddle .

I know it is frowned upon but it is why I keep an open top. I do a safety or newcomers briefing for each new fish upon arrival. Anyway I explain how tall the tank is and that there is no safety net should they get coached into playing flipper or doing any Parkour.

On a serious note - always assumed there was be a loss just didn't know how much. Also didn't know about cheap vs quality egg crate. Learned something new today.

I need to get your coaching technique. LOL. I just lost a clownfish the other day - only the second jumper I've ever had.

 

[Mastiffsrule]

Thanks for another great write up.

Shocked on the amount of loss on the fiberglass. I’m pulling the 1 panel I use in the center of my tank off right now. I had it for cooling and gas exchange since there is not much coral under it and I have glass above the other 2 sections of my tank.

Wow.

 

[ingchr1]

Here's a thread on what I found with my screen tops, it has a couple of iterations.

Screen Top PAR Reduction

I did a test today to see what the difference in PAR was for my tank from screen top on to screen top off. I used a Seneye and the results are shown in the screenshots. The Seneye was kept in the same position on the sand about center tank. For the screen top on I passed the Seneye cord through...

www.reef2reef.com

 

[Fernthereefer]

Thanks for the write up. I use a glass top on my DT... because of its unconventional format I can't make an esthetically pleasing mesh.

The loss of PAR is definitely something to consider....

 

[Dana Riddle]

I wonder, and not for more testing, but the effects of standard layout panel vs. narrow puck style vs. lens. I know with the a360x from Kessil the spread is 130 degrees but adding the lens narrows it and increases par by more focus / direction.

Not sure what effect, if any, it would have to help or not. I guess the loss is the light being blocked so probably doesn't matter.

I'll take a look when I get a chance.

 

[User1]

I'll take a look when I get a chance.

OH - no, sorry. I didn't mean more tests . Please don't. I was just thinking out loud. I actually have an open top and keep fish that are not known to jump. I know that is not a guarantee.

 

[Dana Riddle]

OH - no, sorry. I didn't mean more tests . Please don't. I was just thinking out loud. I actually have an open top and keep fish that are not known to jump. I know that is not a guarantee.

If I remember correctly, the focusing effect by egg crate didn't apply to line sources (fluorescent lamps) as opposed to point sources (MH, and likely LED pucks) but then it has been 25 years, and my memory isn't what it once was.

 

[swiss1939]

If I remember correctly, the focusing effect by egg crate didn't apply to line sources (fluorescent lamps) as opposed to point sources (MH, and likely LED pucks) but then it has been 25 years, and my memory isn't what it once was.

It is not as severe under fluorescent lamps because they are by nature a more soft light source that creates a more even ambient source unlike the reflector or fresnel lenses in singular/point light sources, but still exists. MH and LED definitely suffer more from this as their light is inherently more directional, especially on something like the ReefLED 90 which has all leds behind a rudimentary fresnel lens which serves to focus the light even more directional than leds already are.

In fact, a kind of strange thing happens with fluorescent lights and egg crates.. the effect kinda reverses based on distance from the light. If you place the egg crate right up against the light, it reduces the spread vs holding it 6" away from the light source. This is because the light has more room to bounce around and become more ambient or the equivalent of a larger source when the egg crate is further away from the fluorescent source vs when the egg crate is right up against it. You can test this by holding your hand right up against a fluorescent light and you will have sharper/more contrasty shadows on you hand vs holding it 6" to a foot away from the fluorescent light. You are effectively making an ambient light source less ambient and more directional when you hold the egg crate right up against fluorescent lights.

 

[Kodski]

44% reduction from window screen!

I was using window screen on a tank for a period of time. No wonder I really had to crank up my light. I assumed it was quite a bit, but not close to 50%!

Dana have you tested screen coverings that are often sold for this specific application? IE the netting from BRS or the redsea screen kits? I would assume negligible light loss due to the wider patterns but I'm curious on your thoughts none the less.

 

[Dana Riddle]

44% reduction from window screen!

I was using window screen on a tank for a period of time. No wonder I really had to crank up my light. I assumed it was quite a bit, but not close to 50%!

Dana have you tested screen coverings that are often sold for this specific application? IE the netting from BRS or the redsea screen kits? I would assume negligible light loss due to the wider patterns but I'm curious on your thoughts none the less.

No, I've haven't tested either, but I'll order some next time. Think I'll go for the 1/4" clear mesh.

 

[xabo]

44% reduction from window screen!

I was using window screen on a tank for a period of time. No wonder I really had to crank up my light. I assumed it was quite a bit, but not close to 50%!

Dana have you tested screen coverings that are often sold for this specific application? IE the netting from BRS or the redsea screen kits? I would assume negligible light loss due to the wider patterns but I'm curious on your thoughts none the less.

Pretty much the same with smoke. That's one reason Firefighters remove the window screens when ventilating a room after a fire. The screens reduce the smoke removal by the same 44%.

 

[Calm Blue Ocean]

I have wondered the effect of condensation on glass lids.

 

[Billldg]

@Dana Riddle , when I get my new tank up and running, gonna be awhile, I plan on adding a Octo Lids top, if you have the time maybe you can come over and do test on it.