Eggcrate for focusing light

[DaveS]

Dave,

I don't remember if you were there when Anthony was discussing this, but his statement was to use the light diffusers in the reverse position so they would take the lightbeams that were spreading through the glass (since MH reflectors tend to induce spread) and focus them straight down into the tank.

 

 

Yea I remember him saying that. I thought it was "interesting science" at the time. Kinda like the theory from a new bestseller book about how Asians are good at math because of all the years of farming rice.

 

Maybe this idea for the eggcrate came from thinking that if you take something that works one way and reverse it, it works the other- use a diffuser in reverse and it becomes a focuser. I dunno. I do think that Origami's quick experiment is good enough to bust this myth.

Edited December 11, 2008 by DaveS

[astroboy]

I think the reason your nooks and crannies are better illuminated is because eggcrate is NOT a light focusing device but a light diffusing device. That's generally why they put it on fixtures. If it was meant to be a focusing device, it would be linearly parabolic- like the way T5 reflectors are. As it stands, what eggcreate does is take a linear "point source" and changes it into multiple point sources. Each grid surface is, by reflection/diffusion, a small source of light. As result, you get illumination over a great surface. The drawback is that each surface has less intensity as seen by the empirical results.

 

As Brian said, generally the thick edge of the grating is down, which will tend to scatter the light sideways (and out of the tank). If you put the thin side down it will tend to reflect beams going "sideways" "down" to some degree. As you say, you'd tend to get a (slightly?) more uniform illumination. You're right, this is a diffusing effect, although the increase in uniformity comes from light that would have lost thru the front and sides of the tank. Of course, the crate itself blocks some of the light, and the more I think about it the more I'm sure there's a significant overall loss. It sure looks that way to my eye, for my tank. However, just eyeballing the rock wall at the back of your tank to judge its effects might be misleading.

 

This is a really squirrelly problem.

[Coral Hind]

Just to clear some things up. Eggcrate louver is normally used to direct light downward and not as a general diffuser. Its main purpose is to reduce the glare from overhead fixtures. It was designed to be used with the wider side toward the light. Installed with the narrower side toward the light would make the light spread even less.

[www.fishnreef.com]

Gotta love the club!

[Origami]

Interesting perspective, Astroboy. I do appreciate the thoughts you've offered. Complicated though it might be, it seems that the history of independent measurements taken over the years by others (like rocko) in filled aquariums seems to indicate that the idea of improved efficiency is more legend than fact. That eggcrate somehow focusses the light seems to escape me and the evidence (including these measurements) would seem to support that. Egg crate does not seem deep enough relative to it's width to provide substantial directionality but then, as DaveS notes, it's designed to serve as a diffuser of light in order to provide an even illumination to work surfaces below and to cut down on glare (diffusers do cut down on glare). As such, I would expect that a single egg crate cell distributes light over a broad area, at least the light that makes it out and down. Much of that light is obviously reflected in directions other than down because it's easy to see from many perspectives that the egg crate is well illuminated (that is, bright). (This is probably because the diffuser surface is neither entirely front-surface reflective and because it is not entirely smooth.)

 

It would be interesting to see an analysis that incorporated diffusion, indexes of refraction, and illumination patterns from point sources through different reflectors in these various configurations. I'm not sure that it would change the outcome in any substantial way, however. In the end, I think we will find that the reflector design and its match to the tank application is going to be where PAR efficiencies are gained. Adding an inefficient diffuser like egg crate to the model just doesn't seem to work toward this end.

Edited December 11, 2008 by Origami2547

[astroboy]

Interesting perspective, Astroboy. I do appreciate the thoughts you've offered. Complicated though it might be, it seems that the history of independent measurements taken over the years by others (like rocko) in filled aquariums seems to indicate that the idea of improved efficiency is more legend than fact. That eggcrate somehow focusses the light seems to escape me and the evidence (including these measurements) would seem to support that. Egg crate does not seem deep enough relative to it's width to provide substantial directionality but then, as DaveS notes, it's designed to serve as a diffuser of light in order to provide an even illumination to work surfaces below and to cut down on glare (diffusers do cut down on glare). As such, I would expect that a single egg crate cell distributes light over a broad area, at least the light that makes it out and down. Much of that light is obviously reflected in directions other than down because it's easy to see from many perspectives that the egg crate is well illuminated (that is, bright). (This is probably because the diffuser surface is neither entirely front-surface reflective and because it is not entirely smooth.)

 

It would be interesting to see an analysis that incorporated diffusion, indexes of refraction, and illumination patterns from point sources through different reflectors in these various configurations. I'm not sure that it would change the outcome in any substantial way, however. In the end, I think we will find that the reflector design and its match to the tank application is going to be where PAR efficiencies are gained. Adding an inefficient diffuser like egg crate to the model just doesn't seem to work toward this end.

 

Oh, I certainly didn't mean to imply for an instant that your measurements (and other people's observations) weren't correct or well thought out! If it sounded that way I apologize!

 

I was getting hung up on the notion that having water in the tank would probably let more light out. In my job for the past year we've had alot of things that we thought were minor effects come back and bite us big time months later, so I've just gotten into the mode of nitpicking everything to death without any regard for reality.

[Origami]

... so I've just gotten into the mode of nitpicking everything to death without any regard for reality.

 

No offense taken. The devil's often in the details.

[howaboutme]

Bumping this useful thread. Tom's experiment is post #15. Someone should recreate this w/ LEDs.