anyone use glass mirrors for MH reflectors?
- Thread starter rsteagall
- Start date
Adam
New member
rsteagall,
Glass mirrors aren't as efficient as you might think. The light has to pass through the glass of the mirror.... twice (in and out), so the effect is similar to having double the thickness of glass between your lamp and tank.
Acrylic is marginally better since it is clearer than glass, but it probably would melt from the heat of MH's.
www.aquatictech.com sells reflective aluminum for DIY projects.
HTH
Adam
Glass mirrors aren't as efficient as you might think. The light has to pass through the glass of the mirror.... twice (in and out), so the effect is similar to having double the thickness of glass between your lamp and tank.
Acrylic is marginally better since it is clearer than glass, but it probably would melt from the heat of MH's.
www.aquatictech.com sells reflective aluminum for DIY projects.
HTH
Adam
beaniebeagle
New member
when growing plants in greenhouses, mylar reflects 90-98% of light
a regular mirror is actually less than 90%
there are some acrylic paints that reflect 98%+ reflectance that dont get yellow under UV, I don't know how they will react with saltwater or with the fish
would check out some gardening/greenhouse or growing under lights forums
a regular mirror is actually less than 90%
there are some acrylic paints that reflect 98%+ reflectance that dont get yellow under UV, I don't know how they will react with saltwater or with the fish
would check out some gardening/greenhouse or growing under lights forums
rsteagall
New member
Interesting. I didn't know mirrors were so inefficient. I'll look into using other reflective materials.
Without creating another thread.... How do you guys feel about this retrofit system?
http://cgi.ebay.com/Dual-250-Metal-Halide-Reef-Aquarium-Retro-Kit_W0QQitemZ7740716101QQ
or possibly
http://cgi.ebay.com/36-Metal-Halide-VHO-Retro-kit-new-light-with-bulbs_W0QQitemZ7740690461QQ
Thanks.
Without creating another thread.... How do you guys feel about this retrofit system?
http://cgi.ebay.com/Dual-250-Metal-Halide-Reef-Aquarium-Retro-Kit_W0QQitemZ7740716101QQ
or possibly
http://cgi.ebay.com/36-Metal-Halide-VHO-Retro-kit-new-light-with-bulbs_W0QQitemZ7740690461QQ
Thanks.
hahnmeister
In Memoriam
According to lighting engineers, the best material is mirror polished aluminum.
a4twenty
Premium Member
we're not talking about collecting light for the hubble telescope here. i would stay away from using mirrors to reflect light as they create hot spots, and can be blinding. mylar works great for reflecting light, but considering it is only slightly more efficient than white paint ( 2 - 5 % ) and can pose a fire risk, it's not worth it ( also can create hot spots if it's not laid flat ). your going to have to paint or seal the inside of your canopy anyway, so just use flat white paint. they say that flat white paint reflects 90% of light and diffuses much better than silvery materials.
BeanAnimal
Premium Member
certain white paints are as reflective (or more so) than some shiny metals.
The surface of the reflector has a lot to do with how the light is scatterd as well.
A few percent does matter because the light that strikes the tank is mostly reflected. The biggest hurdle is getting the light to reflect into the tank on as few bounces as possible. This is where the SHAPE of the reflector comes in. The shape of the reflector has EVERYTHING to do with the efficiency of the lighting system. Light leaves the bulb in all directions. It has to be reflected and focused onto the area you want to use it. Light that spills out of the area is wasted. In addition lets look at the "bounce" of the light. Lets say your reflective material is 90% efficient. Light that take 2 bounces to be directed to where it needs to go loses 10% of 100% which is 90 and then loses 10% on the second bounce. The light is now 81% as bright as it was when it left the bulb envelope. In other words you have lost 19% of the original light already. Using the same bulb and different reflector that is say 87% reflective.... In this case you have lost 25% of the original light as compared to the first reflector.
Now remember that those number are not for the whole bulb, just those rays of light that shoot off at that particular angle. If you examine engineered reflectors you will notice that the bulb is placed high up in the reflector. This is so that light that comes off of the bottom half of the bulb strikes a reflecting surface and then the tank, instead of spilling out at a wide angle.
In other words, the best refectors are engineered to focus the light where it is needed in a specific shape. The reflective material is important, but the shape is more important.
Bean
The surface of the reflector has a lot to do with how the light is scatterd as well.
A few percent does matter because the light that strikes the tank is mostly reflected. The biggest hurdle is getting the light to reflect into the tank on as few bounces as possible. This is where the SHAPE of the reflector comes in. The shape of the reflector has EVERYTHING to do with the efficiency of the lighting system. Light leaves the bulb in all directions. It has to be reflected and focused onto the area you want to use it. Light that spills out of the area is wasted. In addition lets look at the "bounce" of the light. Lets say your reflective material is 90% efficient. Light that take 2 bounces to be directed to where it needs to go loses 10% of 100% which is 90 and then loses 10% on the second bounce. The light is now 81% as bright as it was when it left the bulb envelope. In other words you have lost 19% of the original light already. Using the same bulb and different reflector that is say 87% reflective.... In this case you have lost 25% of the original light as compared to the first reflector.
Now remember that those number are not for the whole bulb, just those rays of light that shoot off at that particular angle. If you examine engineered reflectors you will notice that the bulb is placed high up in the reflector. This is so that light that comes off of the bottom half of the bulb strikes a reflecting surface and then the tank, instead of spilling out at a wide angle.
In other words, the best refectors are engineered to focus the light where it is needed in a specific shape. The reflective material is important, but the shape is more important.
Bean
MiddletonMark
Premium Member
Totally agree with Bean.
The difference between a flat reflector, and curved [and various styles] is large, and striking.
Take a look at Sanjay Joshi's research on reflectors [papers, discussions here] as it's incredibly instructive, and IMO will suprise you with the difference between reflectors.
Don't go with glass, and IMO don't cheap out.
You're paying for the power to run the bulb - get every photon you can to your corals. IMO, it's all about efficiency - and trust me, going from a flat white reflector to PFO parallel blew me away - visually far more light, far better distribution - went from dark corners to even light across the tank.
Just my opinon
The difference between a flat reflector, and curved [and various styles] is large, and striking.
Take a look at Sanjay Joshi's research on reflectors [papers, discussions here] as it's incredibly instructive, and IMO will suprise you with the difference between reflectors.
Don't go with glass, and IMO don't cheap out.
You're paying for the power to run the bulb - get every photon you can to your corals. IMO, it's all about efficiency - and trust me, going from a flat white reflector to PFO parallel blew me away - visually far more light, far better distribution - went from dark corners to even light across the tank.
Just my opinon
BeanAnimal
Premium Member
The pipe is not really the greatest shape, but it is better than a flat or odd shaped hood. In the end as long as your happy with your creation, that is all that matters.
BeanAnimal
Premium Member
I also hope that PVC pipe is for fluorescent type bulbs, as PVC and high heat (halides) could spell disaster.
fppf
New member
You can get glass mirrors that are +95%. They are mainly used in stage lighting and solar collectors. Glass mirrors are prefered in solar collectors because aluminum will oxidize and loss efficiency over time and any coatings will do the same. The glass mirrors will hold over time. The main reason there used in stage lighting is to reduce heat. The bigger lights are so intence at the output where aimming mirrors are placed low efficiency mirrors over heat and crack.
MiddletonMark
Premium Member
Good reading on reflectors can be found here:
http://www.advancedaquarist.com/issues/mar2003/feature.htm
Of note is the final measurements on the bottom, where he compares a painted white flat reflector to the other reflector #'s shown. [getting at the efficiency of that]
http://www.advancedaquarist.com/issues/mar2003/feature.htm
Of note is the final measurements on the bottom, where he compares a painted white flat reflector to the other reflector #'s shown. [getting at the efficiency of that]
what do you guys think a mirror is?
the glass is just giving it substance. glass is still clear. its the backing that is reflecting anything at all; and the backing is only as reflective as whatever polished film its made of.
Id bet the high output mirrors are just using starphire glass. but its a mute point for this. you'd be amazed how shiny you can make metal. think of a polished metal car rim(not a chrome rim, but they look the same)
the glass is just giving it substance. glass is still clear. its the backing that is reflecting anything at all; and the backing is only as reflective as whatever polished film its made of.
Id bet the high output mirrors are just using starphire glass. but its a mute point for this. you'd be amazed how shiny you can make metal. think of a polished metal car rim(not a chrome rim, but they look the same)
Adam
New member
fppf,
Specialized optical mirrors are scary expensive. And as an esoteric extension of your point, there are mirrors called "cold mirrors" and dichroic mirrors that are designed to reflect certain wavelengths and transmit certain wavelengths.
In the case of "cold mirrors", they reflect visible light but infrared passes through. Imagine how much energy could be saved on chillers if only a fraction of the heat from lamps was reflected into the tank!
Unfortuantely, the cost of such mirrors is scary prohibitive.
areze,
I think many posters in this thread have made it clear that they understand exactly what a mirror is. In addition to the fact that the reflective coatings probably come in a range of grades... as you yourself said, so does the glass. Even starfire glass is not perfectly clear, so some light is lost as the light passes through.
Adam
Specialized optical mirrors are scary expensive. And as an esoteric extension of your point, there are mirrors called "cold mirrors" and dichroic mirrors that are designed to reflect certain wavelengths and transmit certain wavelengths.
In the case of "cold mirrors", they reflect visible light but infrared passes through. Imagine how much energy could be saved on chillers if only a fraction of the heat from lamps was reflected into the tank!
Unfortuantely, the cost of such mirrors is scary prohibitive.
areze,
I think many posters in this thread have made it clear that they understand exactly what a mirror is. In addition to the fact that the reflective coatings probably come in a range of grades... as you yourself said, so does the glass. Even starfire glass is not perfectly clear, so some light is lost as the light passes through.
Adam
fppf
New member
Yes there is a whole slew of special mirros. They can make a mirror or filter depending who you ask to pass or reflect just about any wavelength you want.
I never said they where cheap. But the mirrors used on solar arrays are not horrible $$$. To get the high numbers they use really thin glass with a silver backing. Most of them are only 1-2 mm thick. Its the silver backing that gets ya.
I never said they where cheap. But the mirrors used on solar arrays are not horrible $$$. To get the high numbers they use really thin glass with a silver backing. Most of them are only 1-2 mm thick. Its the silver backing that gets ya.
BeanAnimal
Premium Member
Most high efficiency mirrors are front coated and used in a sealed invironment. Mirrors that are coated or put behind a glass binder are at a disadvantage, no matter how thin the coating or glass. There are at leat 2 additional angles of incidence that are parasitic to the amount of light reflected to it's final destination. Differetent materials have different critical angles but because both surfaces of the coating are not perfectly parallel planes, some light is bound by the mirror and bounces back and forth between the coating and the protector. Yet more light is scattered off at angles other the angle of incidence because of the uneven surfaces.
This thread has kinda gone from useful to musings about mirrors. Furthermore, a specialzed high efficiency mirror is useless for our purposes. It can not be shaped to maximize the focus where we need it. Remember we are trying to get the most out of a round bulb that radiated in all directions. We ARE NOT trying to transmit a shaft of focused light from point A to point B
The bottom line is that you need to choose a properly designed reflector to maximize the light from your selected material. In our hobby or in our reality there are very few choices to choose from. Polished metal, white or colored paints, and mylar or other flexible plastics are about the only options.
This thread has kinda gone from useful to musings about mirrors. Furthermore, a specialzed high efficiency mirror is useless for our purposes. It can not be shaped to maximize the focus where we need it. Remember we are trying to get the most out of a round bulb that radiated in all directions. We ARE NOT trying to transmit a shaft of focused light from point A to point B
The bottom line is that you need to choose a properly designed reflector to maximize the light from your selected material. In our hobby or in our reality there are very few choices to choose from. Polished metal, white or colored paints, and mylar or other flexible plastics are about the only options.
Adam
New member
Bill,
True, true!!
Thanks for bringing this back to the point.
Anyone who wants to beat this horse any more really must read the work by Sanjay Joshi that is referenced above in this thread. You will quickly see that nit-picking over 1-2% of reflectivity is nothing compared to the 10's of percents that can be had or lost by changing the reflector design.
As for Bill's point about materials choices... when it comes to the reflectors themsleves, polished metal really is the only choice because of the heat involved. Mylar/reflective plastics and paints may be suitable for canopy interiors though.
Adam
True, true!!
Thanks for bringing this back to the point.
Anyone who wants to beat this horse any more really must read the work by Sanjay Joshi that is referenced above in this thread. You will quickly see that nit-picking over 1-2% of reflectivity is nothing compared to the 10's of percents that can be had or lost by changing the reflector design.
As for Bill's point about materials choices... when it comes to the reflectors themsleves, polished metal really is the only choice because of the heat involved. Mylar/reflective plastics and paints may be suitable for canopy interiors though.
Adam
