SolaTubes for reef tanks

[barryhc]

<a href=showthread.php?s=&postid=6281425#post6281425 target=_blank>Originally posted</a> by delnino
I could be a little off here but I would recommend against using mirrored acrylic for any light reflectors. I know that standard glass mirror is terrible for this purpose because it has a black backing that actually absorbs light. A room filled with mirrors appears very dark. A room painted white is very bright. Mirrors are designed to show an accurate reflection and I think the acrylic mirror is made for the same purpose. Polished aluminum, silver oxide coated aluminum, or even white metal will much better I think.

The light never gets to the "backing" because it is reflected from the mirror surface. ( and out of the "mirror filled room" for that matter )

Take a miirror and a white sheet of whatever, and lay them both flat outside on a bright sunny day. Now look into the mirror so that you can see the sun, try the same with the white sheet, if you can still figure out where it's at, and you are not on your way to the hospital.

Questions? > barryhc :beachbum:

 

[hllywd]

I wouldn't bet my life, but if I remember correctly delnino is right concerning the reflectivity of a mirror. The mylar over aluminum type materials are supposed to reflect much more light. The glass itself will absorb some light since it has to travel through the glass twice to go where you want it...

 

[hllywd]

I wouldn't bet my life, but if I remember correctly delnino is right concerning the reflectivity of a mirror. The mylar over aluminum type materials are supposed to reflect much more light. The glass itself will absorb some light since it has to travel through the glass twice to go where you want it...

 

[gatohoser]

I heard that too.

 

[barryhc]

<a href=showthread.php?s=&postid=6292464#post6292464 target=_blank>Originally posted</a> by hllywd
I wouldn't bet my life, but if I remember correctly delnino is right concerning the reflectivity of a mirror. The mylar over aluminum type materials are supposed to reflect much more light. The glass itself will absorb some light since it has to travel through the glass twice to go where you want it...

I think you are getting confused about "dispersing" more light, and a white room will be very bright, in fact the brightest, by way of this "dispersion". Dispersion, however, is not what we are looking for when attempting to "direct" light to a "new location".

Also, the absorbtion of light through "mirror-grade-acrylic" is quite low.

Still, if this doesn't make any sense, then take the prospective materials outside on a sunny day, and look at the suns' reflection, and throw away the ones that don't blind you.

Did you ever notice how bright a white shirt looks under a "black light"? "Perception" is a "multi-edged" sword.

Happy Reef Keeping!!! > barryhc

:beachbum: :thumbsup:

 

[barryhc]

<a href=showthread.php?s=&postid=6292465#post6292465 target=_blank>Originally posted</a> by hllywd
I wouldn't bet my life, but if I remember correctly delnino is right concerning the reflectivity of a mirror. The mylar over aluminum type materials are supposed to reflect much more light. The glass itself will absorb some light since it has to travel through the glass twice to go where you want it...

Good "mirror" is 97% reflective, so how much more reflective is 100%, or "perfect reflection"?

Are we making progress?

> barryhc

 

[hllywd]

Sorry guys I hate to beat this to death but I went back and looked at some of my info on glass mirrors, acrylic mirrors are a little better reflectivity-wise at about 85% where a good glass "plane" mirror is about 80% reflective. A front surface mirror such as a telescope primary or secondary mirror, depending on the coatings and enhancements, can be up to about 98% reflective. Specular aluminum is from about 85% reflective to the high 90%s. Painted steel can be greater than 85% and can be enhanced to over 90%.
The confusion of appearances arises because of the way the light is reflected. A plane mirror reflects the light rays parallel and looks bright, a concave mirror's reflection converges at a focal point and if large enough won't blind you but will set your head on fire when you look at it, a convex mirrors reflection is divergent and will appear less bright. Specular aluminum, and painted surfaces can and usually are more reflective than a "regular" mirror. The difference is the light rays scatter or are more difuse.
Tim

BTW I agree white wouldn't be the way to channel light into a space but neither is a "regular" or "plane" mirror unless you're talking about reflecting the light once. Everytime the light changes direction you'll lose intensity. At 80% that will add up fast.

 

[barryhc]

If we look at "transferrence" of light, it is going to stack up a little bit differently. Firstly I will concede to Hollywood's numbers. And we can get into fine detail on reflectivity, but the "look at the sun" analogy, is going to remain. This redirects, or transfers the light to an "aimed" new location. We can get into exact energy absorption, and therefore supposed effeciencies, by reading the temperature on the back of the surface, but any "mirror surface is going to put many factors of "more" light to the new location relative to the alternative material that is not as "blinding".

Have a great day!! > barryhc

 

[hllywd]

I think there are different ways of resolving this issue to our goal. The manufacturers of the tube skylights as far as I know all use some kind of specular aluminum, I installed a couple 14" Velux "tubes" this past fall that had flexible tubes much like a dryer vent only 14" dia with a shiny aluminum coating. I don't think these deserve consideration for our purposes because my instinct tells me the rigid tube would direct more light where it's desired. I think my 10" rigid Solatube is brighter than the 14" flexible Velux unit. I don't have a light meter but that's what my eyes tell me.
I think these have promise for reducing dependance on artificial lighting but unless a way to implement a larger skylight and get most of the light onto the tank area they will remain suplimental.

 

[barryhc]

<a href=showthread.php?s=&postid=6197689#post6197689 target=_blank>Originally posted</a> by barryhc
For a skylight applicaton, IF you are near a wall, two 4' x 8' sheets for "opposite walls" of mirrored acrylic could be curved in a nearly parabolic curve, from 4' wide at the top, to whatever tank width that you desire, with flat sheets at the sides, to make your "collector-amplifier". If you are 4' square wiyh the skylight, for instance, and run this into a 48" x 18" tank, you have captured 16' sq. ft. of light.

A 10" Sola Tube only delivers .55 sq. ft. per tube, so even if the skylight method was only half as effecient as the Sola Tube, 4 Sola Tubes offer a total of 2.2 sq. ft. of area, whereas the skylight version, even when rated at 50% would effectively deliver 8 sq. ft. of sunlight.

This mirrored acrylic sheet is readily available in 1/8" thick sheets, and is not that expensive. I think the relative effeciency would actually be better than 50%. It would require a bit of "boxing" in the rafters, but it wouldn't be that bad.


> barryhc :beachbum:

Selfexplanatory

 

[goby1]

Actually, a good front-surface mirror can be pretty much 100% reflective. As long as the material is reasonably pure, and the roughness is less than the wavelength of light you want to reflect, you're good to go. Of course, that would be cost prohibitive for the casual solar collector. Edmund optics has cheap parabolic mirrors, FYI.
G1

 

[salty joe]

If your skylight measures 4' x 4', and your aquarium measures 4' x 18", what is the advantage of curving the reflective material in the light tunnel versus running flat panels?

Joe

 

[hllywd]

The idea is to "focus" the light onto a spot the size of the tank.

 

[salty joe]

But the sun does not stay in a fixed position. It seems that the light would be focused at different points in different times of the day. Maybe I'm being really dense here, but I still can't see the advantage of curved panels versus flat tapering panels.

 

[Trickman2]

When I finally get a house and not a condo. I plan on doing the solatubes for my tank.

 

[hllywd]

Salty, The thead is specifically about Solatubes and has been expanded to the large "square" skylight idea. My personal feelings are that the Solatubes are a better idea for the reason you stated although their collection area is limited. The one I installed is not over a tank but over the dining room table where my wife keeps a ficus tree during the months it can't be outside. In bright sunlight it offers a lot of light and it's directional nature isn't affected by the sun's changing position although it's intensity is. It provides about a 6' circle of light on the floor from the 8' ceiling, moonlight is also transmitted enough to light the table at night during the more "full" phases of the lunar cycle. It was very easy to install taking about an hour and a half to complete. I think the application, at least in NW Ohio, is supplimental lighting not a replacement for the artificial lights.

I also think if you can figure out how to make the 4 x 4 hole in the roof and maintain the roof's integrity, keep it from sweating and leaking, and focus the light on the tank, that is an even better idea but due to our winter length of day and timing you still wouldn't completely replace the artificial lights.

Unless somebody comes up with a revolutionary idea for this short of a heliostat and high quality mirrors for a system costing many thousands I'll continue to make my plans for the other $400 worth of Solatubes waiting in the attic for just such a project.

Tim

 

[hllywd]

Trickman, I installed 2 of the 14" Velux units in a condo I built an addition on this past fall. Installation isn't terribly invasive and you don't alter any structural components. Unless your association is different from how they work here you shouldn't have a problem.

Tim

 

[Trickman2]

Wish I could but I am a lower unit and have someone directly above me.

 

[salty joe]

Thanks for the reply Tim.

I understand that on a lot of applications, a flat roof for instance, a Sola tube will collect more light than a conventional skylight of comparable size.

I am thinking of a large skylight facing true south. From the solar panel industry, I found that the optimum angle is easily ascertained. Where I live it is approximately 45Ã"šÃ‚°. In this type of situation, I think any advantage from the Sola tube is negligible.

So back to my question. If the skylight is 4' x 4', and the aquarium is 4' x 18", how could using curved panels in the light tunnel yield more light than flat tapered panels in the light tunnel?

Joe

 

[barryhc]

Joe, it's just a matter of getting that 45 degree condition at the collector lense ( or skylight ) "turned" to match the "level" condition at the top of the tank. ( by way of curving the panels ) Also let's throw out any conception of "parabolic" here while we're at it, that was a poor choice of words, way back, on my part.

Also, the bottom portion of the mirror panels can be made to be more nearly parallel with each other so that the light is "funneled" more directly "down" into the tank, which reduces the amount of light that is able to "escape" through the tank walls.

I hope this is helpful. > barryhc