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Best reflective surface for skylight shaft?
I have a skylight shaft that I've like to maximize the light coming down.
At the bottom is a stained glass window. I could paint the shaft sides gloss white. But what about silver? Is there some reflective sheet metal that I can buy that is even better? A glass mirror would probably be a bit difficult to get up there. Thanks, Don donwiss at panix.com. |
#2
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Best reflective surface for skylight shaft?
I think glossy white paint or silver or even mirrors will not pull more
photons out of the sky than plain white paint. White paint will do the job. -B "Don Wiss" wrote in message ... I have a skylight shaft that I've like to maximize the light coming down. At the bottom is a stained glass window. I could paint the shaft sides gloss white. But what about silver? Is there some reflective sheet metal that I can buy that is even better? A glass mirror would probably be a bit difficult to get up there. Thanks, Don donwiss at panix.com. |
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Best reflective surface for skylight shaft?
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#4
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Best reflective surface for skylight shaft?
"Don Wiss" wrote in message ... I have a skylight shaft that I've like to maximize the light coming down. At the bottom is a stained glass window. I could paint the shaft sides gloss white. But what about silver? Is there some reflective sheet metal that I can buy that is even better? A glass mirror would probably be a bit difficult to get up there. Thanks, Don donwiss at panix.com. Bright and shiny. I saw one of the DIY shows where they installed a skylight that used a round flexible duct to send the light from roof to the room ceiling. It was bright silvery coated like a mirror. Maybe you could get some highly polished stainless steel sheet metal or a bright foil lining. I have no idea where you would buy it, but the silvered Mylar film would work well. The stuff they make balloons from or line potato chip bags. Ed http://pages.cthome.net/edhome |
#5
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Best reflective surface for skylight shaft?
On 30-Jul-2004, Don Wiss wrote:
I could paint the shaft sides gloss white. But what about silver? Is there some reflective sheet metal that I can buy that is even better? A glass mirror would probably be a bit difficult to get up there. It would take a very good quality mirror to reflect more light than a good white paint. Cheap mirrors may only reflect about 70% or less of the light. Buy a high quality white paint and look for one with a high LRV (light reflectance value). IIRC, matt white should actually have a higher reflectance than gloss. Mike |
#6
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Best reflective surface for skylight shaft?
B wrote:
I think glossy white paint or silver or even mirrors will not pull more photons out of the sky than plain white paint. White paint will do the job. Sure, but I'm looking at a table that says white paint has 80% reflectance, vs 86% for aluminum foil and 92% for aluminized Mylar. The mirrorlike Mylar can minimize the number of bounces in the shaft, compared to diffuse white paint, further increasing the intensity at the bottom. A south-facing reflective sunscoop over the skylight can also help. Nick |
#7
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Best reflective surface for skylight shaft?
B wrote: I think glossy white paint or silver or even mirrors will not pull more photons out of the sky than plain white paint. White paint will do the job. It is not a question of pulling photons out of the sky. It is a question of moving the ones that you do have in the most efficient manner. There are much better materials than white paint to do the job. Depending on the particular pain and gloss, it is maybe 75 to 80% efficient. I don't have the specs on a mirror, but I'd guess it to be over 90%. |
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Best reflective surface for skylight shaft?
Don Wiss wrote:
I have a skylight shaft that I've like to maximize the light coming down. At the bottom is a stained glass window. I could paint the shaft sides gloss white. But what about silver? Is there some reflective sheet metal that I can buy that is even better? A glass mirror would probably be a bit difficult to get up there. Remember the foil reflecting material used over car dashes? Use that or similar for max reflectance. However, max reflectance may not give you the max output at the bottom because they are so directional. Think of a mirror...you have to angle it around to reflect the source light where you want it to go. For your purpose, a non specular (not glossy) white or aluminum paint would probably be best due to the usual shape of a skylight shaft. -- dadiOH _____________________________ dadiOH's dandies v3.0... ....a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico ____________________________ |
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Best reflective surface for skylight shaft?
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#10
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Best reflective surface for skylight shaft?
On 31-Jul-2004, "Edwin Pawlowski" wrote:
Depending on the particular pain and gloss, it is maybe 75 to 80% efficient. I don't have the specs on a mirror, but I'd guess it to be over 90%. Paints can be up to 90% reflective. These are high-quality titanium oxide based paints, of course. There are other oxides as well, but the Ti stuff is probably easier to find. Mirrors are highly variable, depending on the quality of the coating. Getting over 90% is quite difficult and expensive. I remember paying quite a premium to get a telescope mirror that was over 90% - the standard quality (still higher than, say, a bathroom mirror) was in the mid 80s. Dollar for dollar, paint is a much better deal and easier to install. Mike |
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Best reflective surface for skylight shaft?
dadiOH wrote:
Don Wiss wrote: I have a skylight shaft that I've like to maximize the light coming down... Remember the foil reflecting material used over car dashes? Use that or similar for max reflectance. However, max reflectance may not give you the max output at the bottom because they are so directional. Not according to the usual lightwell calculations. Think of a mirror...you have to angle it around to reflect the source light where you want it to go. For your purpose, a non specular (not glossy) white or aluminum paint would probably be best due to the usual shape of a skylight shaft. I doubt that. Can you find a specific example that makes your claim true? Nick 10 RHO=.9'lightwell wall reflectance 20 W=4'lightwell width (feet) 30 L=8'lightwell length (feet) 40 C=4'concentration factor 50 EC=.8'concentrator efficiency 60 TFLUX=8000*W*L*C*EC'total flux entering well (FC) 70 FOR F = 1 TO 8'floor number 80 H=8*(8-F)'lightwell depth (feet) 90 R=5*H*(W+L)/(W*L)'well cavity ratio 100 E=EXP(-.0443*R/RHO)'transmission 105 PRINT F,E 110 ATTN=ATTN+1/E'cumulative attenuation 120 NEXT 130 ATA=ATTN/8'average attenuation 140 PRINT ATA'average attenuation 150 AREA=32^2*8'floor area (ft^2) 160 ER=.9'secondary reflector efficiency 170 PRINT ER*TFLUX/ATTN/AREA 180 ER=.6'eg 2 wall bounces, and a bottom reflection... 190 PRINT ER*TFLUX/AREA Floor Lightwell number Transmittance 1 .0056940 2 .0119144 3 .0249304 4 .0521655 5 .1091535 6 .2283978 7 .4779098 8 1 Average diffuse well attenuation: 41.9 Illumination from diffuse well: .268 footcandles Illumination from mirror well: 60.0 footcandles(?) Nick |
#12
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Best reflective surface for skylight shaft?
Michael Daly wrote:
...I'm looking at a table that says white paint has 80% reflectance, vs 86% for aluminum foil and 92% for aluminized Mylar. Considering you can see through aluminized Mylar, I have my doubts about this claim. Full sun is about 10,000 footcandles. We can see in 0.1 FC, ie we can "see through" something that's 99.999% reflective. Consider what they cover telescope observatories with. The domes are almost always painted white with a high-titanium content paint. They are trying to reflect as much heat and light as possible in order to keep the observatory from heating up during the day. When have you ever seen them cover it with a mirror finish? That's not easy to do. The mirrorlike Mylar can minimize the number of bounces in the shaft, compared to diffuse white paint, further increasing the intensity at the bottom. Only if you can get it nice and smooth. I disagree. Wrinkles make little difference. Nick |
#13
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Best reflective surface for skylight shaft?
On Sat, 31 Jul 2004 15:44:05 GMT, Michael Daly wrote:
On 31-Jul-2004, "Edwin Pawlowski" wrote: Depending on the particular pain and gloss, it is maybe 75 to 80% efficient. I don't have the specs on a mirror, but I'd guess it to be over 90%. Paints can be up to 90% reflective. These are high-quality titanium oxide based paints, of course. There are other oxides as well, but the Ti stuff is probably easier to find. What is the paint they use when they paint flat roofs? Mine was just painted silver, and checking out the job just now I find it very reflective. Certainly paint would be the easiest. Are these titanium oxide paints readily available in my local hardware store? Don donwiss at panix.com. |
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Best reflective surface for skylight shaft?
dadiOH wrote:
...max reflectance may not give you the max output at the bottom because they are so directional. Not according to the usual lightwell calculations. ...a non specular (not glossy) white or aluminum paint would probably be best due to the usual shape of a skylight shaft. I doubt that. Can you find a specific example that makes your claim true? Can you line a skylight chase with mirrors (or even specular reflectors) so they reflect the skylight opening to the ceiling opening? Think "non-imaging." Direct sun aside, the question is: "Can a lightwell with diffuse reflective walls move more lumens into a room than one with specular walls, given a skylight that collects a certain solid angle of diffuse isotropic sun?" Intuitively, light rays enter the skylight from all directions. If the lightwell is vertical, vertical rays from overhead sky pass all the way down the well with no reflections in either case, like shining a laser down a pipe. Slightly off-vertical rays are reflected from the walls far down in the lightwell. More tilted rays hit the walls nearer the top. Specular reflectors pass these rays downwards with little intensity loss. Diffuse reflectors scatter the light all over the place--down, up, and horizontally to adjacent walls... We could make this more mathematical, if you like. Nick |
#16
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Best reflective surface for skylight shaft?
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#17
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Best reflective surface for skylight shaft?
On 31-Jul-2004, Don Wiss wrote:
What is the paint they use when they paint flat roofs? Roof paint. :-) Mine was just painted silver, and checking out the job just now I find it very reflective. The full moon looks almost white, but is something like 10-15% reflective and is quite black (check it tonight - it's a blue moon, BTW). Better check the actual LRV of the paint. Certainly paint would be the easiest. Are these titanium oxide paints readily available in my local hardware store? Many good quality white paints use TiO2. Cheaper ones use clays and stuff. Contact the paint manufacturers for this info. They can tell you which ones are the highest reflectance. This data is available for architects and interior designers. Mike |
#18
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Best reflective surface for skylight shaft?
wrote:
Specular reflectors pass these rays downwards with little intensity loss. Diffuse reflectors scatter the light all over the place-- down, up, and horizontally to adjacent walls... Agreed. But the difficulty would be to get the specular reflectors to collect the light from source and direct it to where desired. Keeping in mind that it is a skylight in (presumably) a home. Actually, if I were the OP and wanted to light a stained glass window in the ceiling I probably would have scrapped the skylight in favor of artificial, controllable light. We could make this more mathematical, if you like. Not me, I = R is about my limit -- dadiOH _____________________________ dadiOH's dandies v3.0... ....a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico ____________________________ |
#19
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Best reflective surface for skylight shaft?
Don Wiss wrote:
I have a skylight shaft that I've like to maximize the light coming down. At the bottom is a stained glass window. I could paint the shaft sides gloss white. But what about silver? Is there some reflective sheet metal that I can buy that is even better? A glass mirror would probably be a bit difficult to get up there. Thanks, Don donwiss at panix.com. Think LOTS of optical fibers. |
#20
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Best reflective surface for skylight shaft?
Don Wiss wrote:
I have a skylight shaft that I've like to maximize the light coming down. At the bottom is a stained glass window. I could paint the shaft sides gloss white. But what about silver? Is there some reflective sheet metal that I can buy that is even better? A glass mirror would probably be a bit difficult to get up there. Thanks, Don donwiss at panix.com. Or a sunlamp in the shaft. Hmmm. Can one get a REVERSE photocell? |
#21
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Best reflective surface for skylight shaft?
Michael Daly wrote:
Full sun is about 10,000 footcandles. We can see in 0.1 FC, ie we can "see through" something that's 99.999% reflective. I can see thru some aluminized mylar in a dimly lit room. My guess is that these are no more than 50% reflective. You might see 0.1 FC in a 5 FC room through a 2% transmissive film. High-reflective aluminized mylar is harder to get and more expensive. If you're going to recommend Al mylar, you have to be specific about the quality and reflectivity. I like Duraflex from Graphic Arts Systems in Cleveland. About 10 cents/ft^2 in 0.002"x54"x100' rolls. It's a myth that mirror finishes (metallic coatings, polished metal etc) are great reflectors of heat and light. Good quality white paint can outdo mediocre mirror finishes easily and are often a lot cheaper. Duane Johnson gets great results with Mylar heliostat mirrors. Nick |
#22
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Best reflective surface for skylight shaft?
dadiOH wrote:
wrote: Specular reflectors pass these rays downwards with little intensity loss. Diffuse reflectors scatter the light all over the place-- down, up, and horizontally to adjacent walls... Agreed. So a lightwell lined with mirrors acts like a crab trap for entering rays. Rays enter, but they never come out. They are all passed downwards, with more reflections for rays from lower sky elevations and fewer for rays from higher elevations. But diffuse reflectors scatter light back up and out of the well. That seems like enough to convince most people that specular lightwells deliver more light, without any math... But the difficulty would be to get the specular reflectors to collect the light from source and direct it to where desired. I'm assuming that part is the same for the diffuse and specular lightwells, that indirect sun rays come equally from all over the sky hemisphere, and each point on a diffuse reflector reflects each ray out from its wall equally over its hemisphere, but a specular reflector beams each ray downwards with an angle of reflection that equals the angle of indicence. Always downwards, never upwards, because of the way rays enter a lightwell with parallel sides. ...if I were the OP and wanted to light a stained glass window in the ceiling I probably would have scrapped the skylight in favor of artificial, controllable light. That might be nice at night. A specular lightwell with no diffuser at the bottom might have glare problems in direct sun. SunOptics makes skylights with lots of "microprisms" that spread direct sun about 30% more efficiently than white plastics with bubbles inside. They produce enough skylights every week (Wal-Mart is one of their customers) to offset 1 megawatt of peak electrical lighting power, without any government subsidies. Nick |
#23
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Best reflective surface for skylight shaft?
On Sat, 31 Jul 2004 18:23:57 -0400, "dadiOH" wrote:
Keeping in mind that it is a skylight in (presumably) a home. Yes, a 1892 row house in Brooklyn. Actually, if I were the OP and wanted to light a stained glass window in the ceiling I probably would have scrapped the skylight in favor of artificial, controllable light. But the shaft is only a couple feet deep (the thickness of the roof). The amount of light that comes in would cost a fortune to replace with artificial. And the skylight is orginal, just I replaced the outside glass with an InsulaDome. Don donwiss at panix.com. |
#24
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Best reflective surface for skylight shaft?
Don Wiss wrote:
But the shaft is only a couple feet deep (the thickness of the roof). The amount of light that comes in would cost a fortune to replace with artificial. And the skylight is orginal, just I replaced the outside glass with an InsulaDome. Well, there's my problem...I was thinking of my own that come down to a dropped ceiling in hall, etc.. Shafts are 6-8'. -- dadiOH _____________________________ dadiOH's dandies v3.0... ....a help file of info about MP3s, recording from LP/cassette and tips & tricks on this and that. Get it at http://mysite.verizon.net/xico ____________________________ |
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