Mirrors for growing, definitive answer..

So I known this is a repeat of the dozens of other threads with the same title, and to be fair I have read a lot of them before posting this. The problem I have with the answers is most of them give out wrong information.

While I don't really have any experience growing, I did re-read my physics book chapter on reflectivity. So here are a few misconceptions often posted: mirrors don't reflect as much light as say mylar, that is almost always incorrect, if a mirror has a silver back (which most mirrors these days do) they reflect about 95%+ of the light. This can easily be tested by taking a lux metering of the reflected light, you won't notice a difference from that of the source.

Second less obviously wrong answer is that mirrors don't reflect the right spectrum, that is also incorrect, any reference that I read says mirrors reflect the same wavelength (spectrum) that the source emmits. Logically, if it didn't emit the right spectrum as in if it absorbed some part of it, then the reflected part would lack that color, so the light would be bluish or reddish, common experience shows that wrong.

Third one is that glass in the mirror somehow absorbs/stops/changes the light wave, that is also not true. Metal halide lamps and high pressure lamps have pretty thick glass/plastic covers which are made of much lower quality glass then mirror glass, and they don't pose a problem.

And lastly a more valid argument of hot spots, this might be true, but !, this could be easily corrected with proper tilting/positioning with correct angles. You can't just place them on walls, which is how I think most of these erroneous arguments got started, if you don't tilt them the right way, the reflected rays won't bounce in the right direction!

I've read one thread where a guy said his mirror reflected less then a white wall, I guarantee that he measured from the wrong perspective and had the mirror flat against the wall! If you measure in the wrong spot then it will show the rating of the surface it's reflecting, if it's reflecting a part of the grey ceiling for example it will show the luminosity of the cieling, which could be much lower then the light.

So all in all I'd like to to get some decent answers, or at least a more logical scientific explanation as to why it should not be used. To be honest I think even hot spots are a myth, a flat mirror doesn't focus light, the light rays it reflects are parallel to each other, the mirror has to be curved to focus, and in a small mirror lets say a foot by a foot will have an almost perfectly flat surface, and it could be easily tested just by looking at the reflected light on a clean sheet of paper.

I'm not just asking this for theoretical reasons, I'm starting a one plant grow in a wooden box in my apartment, I can't have more then one or two bulbs as I live with my parents and I can't hit the electric bill by anything more then a few dollars. So I need to duplicate the light source, without actually using more power, so right now single light bulb right overhead and two correctly calibrated, tilted mirrors on each top corner is the plan that im charting out. I'd like to get some decent answers to this one without too much guess work.

The negligible difference doesn't really justify the cost of true mirrors over Mylar. Also, Mylar or white paint is much easier to work with than a room covered in mirrors. I guess there could be applications for a smaller grow box like your goin with.

None of these things are going to increase the actual power your light provides in the significant way you're thinking. I doubt its going to increase your yield vs white paint.

I like to use white plastic shower curtain liners. Very cheap and quite flexible.

Be very careful growing in a location that is not yours. Without your parents consent it is quite disrespectful.

Mirrors absorb light far more so than they reflect it.

flat bright white ceiling paint

Yes it will work if you can keep moisture/water droplets off the glass,no the extra 5-10% even if you buy an outer coated mirror reflectivness wont justify the price. It would cost me 10 1000watt hps to line my closet with quarter wave parabolic mirrors. I actually tried making a grow light fixture with cfl's and a home mirror, long story short, my day and night temps have enough gap to fill the hanging mirror with water and moisture by morning then once the lights come on, the water drops into the lights. I gave up and painted it white, whats funny is i swear the beam looked brighter when i painted it white without the mirror. I think it had alot of molecular light loss through the glass with CFL's, it seems like the light reflected was not reflected downwards.

Panda film 20x10 sheet for 20$

Wavels said:

I like to use white plastic shower curtain liners. Very cheap and quite flexible.

Be very careful growing in a location that is not yours. Without your parents consent it is quite disrespectful.

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Listen to this. You are risking the forfeiture of your parent's house by growing in there. Not trying to judgmental cause I did plenty of crazy things as a kid, but maybe this is something you hold off on for a few years.

Thanks for all the quick replies, didn't expect so many to be honest, great forum. The thing is it's going to be a small plant, maybe 12 inches tops, I will let it grow a bit and put on 12/12 in about 2-3 weeks. My goal is to extract as much crop as possible and for some reason I think that with 1 or 2 light bulbs and just white paint only the few top leaves will have any decent buds. I'm really relying on the bottom branches to come through here as well to make it worth it.

@Southerner I understand what you guys are saying, but I have been smoking for a while in the house and I have all the proper precautions in place already. I will have a perfectly insulated box with an inflow fan pointed up, and and outflow fan that will run through moist carbon filled container, a small version of which I built to dispell the smoking smell and it works like a charm, it will lead outdoors. My pot size will be about 6 inches wide, maybe 1/3 gallon capacity, so really it will be a tiny plant as I understand that it's a dangerous operation if not done properly, not to mention I live in NYC and mj laws are nowhere near leglaization.

I got insipred by the 1 oz chllange, https://www.icmag.com/ic/showthread.php?t=51480, a really interesting thread if anyone's interested.

@Cobnobuler that's just not true, mirrors reflect more light then any other surface, besides higher quality mirrors.

@SPLFreak808 that's intreseting, so you're saying there's precipitation on the mirror? How would this happen though? Mirror would most likely be warmer then ambient temperature, how would it precipitate anything? But this leads me to a side question, I'm thinking of a hydroponic system, but I would insulate the roots from the leaves, so there wouldn't be too much moisture in the leaf "compartment" anyways besides ambient room humidity, would that be enough or does it need more moisture?

PS @SPLFreak808, the reason it looked brigher is because plain white color reflects things in a diffuse pattern, where as mirror reflects at only specific angles. What that means is that once the rays bounce off the walls, they bounce in different directions a lot of which end up in your eyes, that by itself shows that it's less powerful as imagine how much of that light that's hitting your eyes could have been aimed at the plant.

Indole8 said:

@Cobnobuler that's just not true, mirrors reflect more light then any other surface, besides higher quality mirrors.

.

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Really...?? OK That makes it hard to understand why nobody uses them then because they absorb more light than they reflect. Nobody ( cept you of course) has mirrors in their grow room. If they were the least bit beneficial, at least a few people would.

https://www.rollitup.org/t/reflective-materials-using-mirrors.402912/
https://www.rollitup.org/t/reflective-material-mirrors.231188/
https://www.rollitup.org/t/myths-about-mirrors.362629/
https://www.rollitup.org/t/mirrors-instead-of-mylar.53358/
https://www.rollitup.org/t/mylar-vs-orca-grow-film-vs-flat-white-paint.398859/

Indole8 said:

Thanks for all the quick replies, didn't expect so many to be honest, great forum. The thing is it's going to be a small plant, maybe 12 inches tops, I will let it grow a bit and put on 12/12 in about 2-3 weeks. My goal is to extract as much crop as possible and for some reason I think that with 1 or 2 light bulbs and just white paint only the few top leaves will have any decent buds. I'm really relying on the bottom branches to come through here as well to make it worth it.

@Southerner I understand what you guys are saying, but I have been smoking for a while in the house and I have all the proper precautions in place already. I will have a perfectly insulated box with an inflow fan pointed up, and and outflow fan that will run through moist carbon filled container, a small version of which I built to dispell the smoking smell and it works like a charm, it will lead outdoors. My pot size will be about 6 inches wide, maybe 1/3 gallon capacity, so really it will be a tiny plant as I understand that it's a dangerous operation if not done properly, not to mention I live in NYC and mj laws are nowhere near leglaization.

I got insipred by the 1 oz chllange, https://www.icmag.com/ic/showthread.php?t=51480, a really interesting thread if anyone's interested.

@Cobnobuler that's just not true, mirrors reflect more light then any other surface, besides higher quality mirrors.

@SPLFreak808 that's intreseting, so you're saying there's precipitation on the mirror? How would this happen though? Mirror would most likely be warmer then ambient temperature, how would it precipitate anything? But this leads me to a side question, I'm thinking of a hydroponic system, but I would insulate the roots from the leaves, so there wouldn't be too much moisture in the leaf "compartment" anyways besides ambient room humidity, would that be enough or does it need more moisture?

PS @SPLFreak808, the reason it looked brigher is because plain white color reflects things in a diffuse pattern, where as mirror reflects at only specific angles. What that means is that once the rays bounce off the walls, they bounce in different directions a lot of which end up in your eyes, that by itself shows that it's less powerful as imagine how much of that light that's hitting your eyes could have been aimed at the plant.

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Where i live, everything sweats with a good range of temperature difference. High humidity+hot sun after a night of 60f is more then enough for my enclosed case to collect moisture on the glass and drop water on the lights, or fog up my car window, hell i cant even see my bathroom mirror clearly if i wake up from 8-9am. The sun just heats everything too fast.

Also yes, when i tried the mirror, it seemed to reflect the light back into the fixture through the walls of the fixture. Which is tricky to tell staring right at the damn thing, but easy to tell doing a side by side comparing brightness at the bottom on my conopy.

Mirrors accuratly reflect light, matt white walls and mylar scatter light.

My point is you wouldnt use mylar to make a bulb reflector the same way as you wouldnt use a mirror as a grow room wall but a mirrored surface makes a great reflector (shiny foil behind the mirror i.e. a reflector).


Lasers use mirrors as they dont scatter light beams and what you want a concaved reflector to do (probably making hotspots).
Mirrors would make inefficient grow room walls but not to say they wouldnt work to a point maybe giving slight hotspot issues. Ive always found in a hot sunny place i feel cooler by a white wall than i do a mirrored wall.

Somewhere in what ive said theres a good point, if you can make sense of it id be very gratefull just im wayyyy stoned

OK kid, put the textbook down.

Yes, you are right, a parabolic mirror will reflect light most efficiently. Look at the reflector series LEDs. As you're only growing approximately 1 sqft plant then a 150-200watt rated led would work great for you. You want approximately 70-80 watts actual draw for maximum yield. For a grow that tiny one of those co2 bio bucket type things would actually work.

Glass does absorb UV light I believe, most LEDs don't have it though.

Look at a psychometric chart little genius, the warmer air is the more water it holds. Dewpoint is the temperature at which water condensates. Glass does not hold heat very well, and so when the lights go out it cools more rapidly than the air and bam. Once the glass cools enough the water will condensate on it. To stop this from happening you need a heater on a thermostat to maintain temperature.

Except that your plants transpirate and so the moisture in the air is going to condensate somewhere unless you keep humidity low, for your grow one of those odor absorbing dohickies for rvs will work.

If you get caught remember that your father brought you into this world, he can take you out of it and make another one to replace you. If my kid did something like that in the home I provided for him through my hard work I'd end him.

ShirkGoldbrick said:

Look at a psychometric chart little genius, the warmer air is the more water it holds. Dewpoint is the temperature at which water condensates. Glass does not hold heat very well, and so when the lights go out it cools more rapidly than the air and bam. Once the glass cools enough the water will condensate on it. To stop this from happening you need a heater on a thermostat to maintain temperature.

Except that your plants transpirate and so the moisture in the air is going to condensate somewhere unless you keep humidity low.

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Hmm ive had mirrors in grow rooms which never had any of this happen, are you saying mirrors could pool water then drip on a ballast and cause electrical faliure maybe scary ass fire?

SPLFreak808 said:

Also yes, when i tried the mirror, it seemed to reflect the light back into the fixture through the walls of the fixture. Which is tricky to tell staring right at the damn thing, but easy to tell doing a side by side comparing brightness at the bottom on my conopy.

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Your light source was closer than the focal point of the mirror which depends on the radius, this creates a virtual image and doesn't really reflect.

2Hearts said:

Hmm ive had mirrors in grow rooms which never had any of this happen, are you saying mirrors could pool water then drip on a ballast and cause electrical faliure maybe scary ass fire?

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Sure, if you don't maintain consistent temperatures or your humidity is too high or the mirrors are on the exterior cold walls which act as a heatsink making the mirrors always colder.

I blame dark matter.

2Hearts said:

Hmm ive had mirrors in grow rooms which never had any of this happen, are you saying mirrors could pool water then drip on a ballast and cause electrical faliure maybe scary ass fire?

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Yea it was dangerous! 250cfm exhaust was right above the mirror so overnight so it constantly had air turbulence around it keeping it cooler then the whole sealed closet, once the lights come on, takes about 10 mins then drip! Lucky i was only using cfl's and its only like 6-8 drops of water. keep in mind the lowest my humidity can get on a good day is 65%. It is ALWAYS 65-95 year around. *edit- im willing to give another fixture a go, but this time i will have to seal it air tight and throw a 2a breaker inline.

ShirkGoldbrick said:

I blame dark matter.

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Ahh Dark matter, we wait for one of many theories to be right (or wrong).

How dare you blame dark matter for it possibly is the missing link in unified theory.

You sir are not welcome at CERN large hadron collider!

SPLFreak808 said:

Yea it was dangerous! 250cfm exhaust was right above the mirror so overnight so it constantly had air turbulence around it keeping it cooler then the whole sealed closet, once the lights come on, takes about 10 mins then drip! Lucky i was only using cfl's and its only like 6-8 drops of water. keep in mind the lowest my humidity can get on a good day is 65%. It is ALWAYS 65-95 year around. *edit- im willing to give another fixture a go, but this time i will have to seal it air tight and throw a 2a breaker inline.

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Fucking mirrors man, id hate them for this reason if they didnt make me look so good