Mylar reflects 90%-98% of light, depending on the quality. A domestic glass mirror reflects less than 90%. Don't be fooled by the fact that a glass mirror is so flat. You're not trying to form an image of the light bulb on a particular leaf, just trying to get the light back in the general direction of the leaves instead of out the door.

The problem with the Mylar is that I can't get it to lie flat on the wall, therefore it doesn't evenly distribute the light.

I think you're getting obsessed about making a smooth surface when it isn't necessary. You are putting the reflector on all the walls and the ceiling, right? So you don't need a perfect mirror reflector, just anything that bounces back as much light as possible, direction isn't important. A "wrinkled" or diffuse reflector will reflect light randomly in all directions, and anything that doesn't hit the plants first time will just bounce back off another wall. A mirror type reflector will only reflect light from a lamp to a plant from one particular spot, light hitting it anywhere else will be reflected somewhere else and need to be reflected several more times to get to the plant. A mirror reflector gains nothing unless it is specially shaped to focus the light. Check out some large commercial light baffles, many of them are deliberately not smooth and shiny.

Personally, I'd just paint the whole thing white. You can get acrylic paints with 98%+ reflectance that don't get yellow under UV. Save the shiny stuff for making reflectors that need to focus light such as a parabolic hood over a bulb.

Obsessed indeed.

Like Shrubmeister, I'd paint everything in a semi-gloss ultra pure white base.

Sam

98 % reflectance ?

Got any brand names?

I happen to have six panels of 6.5 x 3.5 ft. two way mirrors lying around.

I put one behind the light rack on Thursday, and it reflects LESS light than the white painted wall.

The dang thing's too heavy to move again, so I'm thinking of taping Mylar to it. Or if I can find that high-reflective paint... I'll just add a coat of paint to the glass. Easier than painting concrete blocks, probably.

And for fun, I've got these mini glass beads you can sprinkle on paint to make it reflect at night. Scatter the light around, on purpose.

Or, I've also got Aluminum additive for paints. Turns out this particular stuff is dangerously flammable, so I probably won't use that, come to think on it.

Well, this stuff claims 98.9% reflectance, but it may be overkill for a plant room :) You should be able to get around 90% reflectance with a standard acrylic paint from a box store, well over 80% with any brilliant white paint. I mention the acrylic paints because many domestic white paints will quickly go yellow under metal halide lighting. Your choice whether to spend a bit on the paint, or resurface the room each year.

I purposely crunch, fold or wrinkle it up, plus it's the cheap stuff.

Mark

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Hairmetal-

2-way mirrors will reflect MUCH less than even a standard mirror because it lets light through the reflective side. While a regular mirror would reflect a lot more, I think it's way into the overkill zone. Regular old white paint will do just fine as will mylar.

What are you growing that needs so much light, pot? :-] Just kidding about the pot, but what types of plants are your concentrating on?

Sam

I vote for real mirrors on the walls and ceiling. Then when you get tired of growing plants in it you can convert it into a bedroom.....

paint the room white...

Foylon is a more rugged material than mylar and about as reflective. But I agree that painting the room white is saner and for practical purposes as effective. I had a room divider made with one side lined with Foylon; I can place it right alongside the plant table, and in any case the far wall is lined with bookshelves.

Just for the record-I am growing citrus and a few tropicals, plus using the edges of the lighted area (I have a 1000W MH light) to overwinter a Ficus benjamina and a couple Chlorophytum. The citrus plants are getting too large and next year I will probably have to enlarge the area and raise up the light which will decrease the intensity just to make sure I can cover the canopy. I figured mirrors would help alleviate that issue. I have picked 3 sweet oranges this WINTER under the lights. The light intensity is about 4800 foot-candles at the tops of the plants and maybe 1100 on the lowest interior leaves. Overkill?? Maybe-but I get oranges when it's zero degrees outside!!! They will go outdoors in summer and the light will get a rest (it will be turned off from mid May thru early October).

QUOTE:
"I'd paint everything in a semi-gloss ultra pure white base"

best advice, i use flat.

I choose semi gloss because of it's resistance to water and it's resistance to staining/ease of cleaning. It may not yield the ultra best reflectivity, but it will be easier in the long-run, maintenance wise.

Sam

GaWd: That makes sense, but for best reflectivity it is flat white.

Okay, I think the most important question of this topic is, where do you buy all this stuff, particularly mylar?

I converted a closet to a grow room--painted it all flat white, but since I have to have a way to bring in fresh air and exhaust hot air--closing the door is no good. I was thinking about attaching the shiney emergency blanket to a very opague standard blanket and draping that across the door opening--allowing the air ducts to come in at the bottom (sealed off, of course, to keep light from getting into the room.) After seeing the lining of grow tents with a very dimpled mylar--I thought I should heavily wrinkle my mylar-like blanket before putting it up. That would seem to be the best way to replicate the grow tent walls. No?

I recommend buying myler blankets that are sold on the walmart website. They are super shiny and ones I purchased from a survival website... theirs is dull and barely a shine to it.

I just placed one behind the plants with lights in front and I am seeing spots now due to how well it shines. Folks... white glossy walls can NOT touch what a myler can do. I've tried mirrors in past and doesn't work near as well as a myler.

I'm going to ask for permission to tape one against the wall on my patio since 1 section only receives about 4 hours of sun and I feel it will help some plants I may not have the room for to get 6+ hours. I live in an apt complex.