Who knows where to buy mylar?

BigBudBalls said:

I
3/4 of the curve of that last PDF is in the near and mid IR range! Its meant to reflect *heat* aka IR It goes out past 2200nm

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No, it's meant to reflect visible light where the vast majority of the light from the sun reaches earths surface through the atmosphere. Almost all mid-IR is actually absorbed by the atmosphere and they just extended the chart out. A quick test with my lab gear will confirm the 85-90% reflectivity (I'm an engineer).

One last thing to keep in mind BigBudBalls in terms of heat, keep in mind that mylar has a broad band reflectivity that extands out to far-IR which would be lower temperature heat. It's likely the case that mylar is going to reflect more heat than white paint. A HPS light as a black body radiation source does not give off much mid-IR, it does give off a lot of far-IR.

JustBaked said:

Im using a cardboard box so im gonna need somethin that wont create hotspots and somehow fuck up my box. Also, i need to find a way to mount an exhasut fan near the top of my box, but im having trouble thinking of a way to support the weight of the fan... any ideas?

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Whoa. You're going to grow in a cardboard box?

I'm surprised no one else has commented on the fact that he's planning to grow in a CARDBOARD BOX.

I'm not a scientist but doesn't cardboard burn fucking easy?

Well if you wanna burn your place to the ground then go for it..

Not even considered getting a plastic toy box?

Maybe making a wooden box out of old crates?




Anything?

Yea, I'm piecing together 6 egg boxes. I don't really see why it would be a problem that the box is made of cardboard. If your thinking its gonna catch on fire, wood is also quite flammable, and i don't really see how it would catch on fire in the first place. I'm using cfls and plan on having good ventilation so heat really shouldn't be a problem. I think I'm going to go with the roof coating, for only a 5-10% difference I'll save myself the hassle of messing with mylar. Thanks again for all the help.

techhead420 said:

No, it's meant to reflect visible light where the vast majority of the light from the sun reaches earths surface through the atmosphere. Almost all mid-IR is actually absorbed by the atmosphere and they just extended the chart out. A quick test with my lab gear will confirm the 85-90% reflectivity (I'm an engineer).

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Wait. In a grow room its meant to reflect visible. But on a roof, its looking to reflect IR. Nut much heat in visible. IR holds the vast majority of heat from all I've read/known. (I could be wrong. An engineer? Of? No shot at ya! I dig ya, and ya seem good. put me in my place! I just wanna learn all I can)

I work on IR lasers for cutting metal. I'm a field engineer. Been in optics for 15+ years

(oh, we are talking about the roof paint, yes? if not, disregard )

JustBaked said:

Yea, I'm piecing together 6 egg boxes. I don't really see why it would be a problem that the box is made of cardboard. If your thinking its gonna catch on fire, wood is also quite flammable, and i don't really see how it would catch on fire in the first place. I'm using cfls and plan on having good ventilation so heat really shouldn't be a problem. I think I'm going to go with the roof coating, for only a 5-10% difference I'll save myself the hassle of messing with mylar. Thanks again for all the help.

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Density will slow combustion. Put a lighter to the center of a piece of plywood for 3 minutes. The to the center of a piece of cardboard for 3 minutes. Afterwoods, whats left of both?

I'm taking bets.

Fahrenheit 451 !!

BigBudBalls said:

Wait. In a grow room its meant to reflect visible. But on a roof, its looking to reflect IR. Nut much heat in visible. IR holds the vast majority of heat from all I've read/known. (I could be wrong. An engineer? Of? No shot at ya! I dig ya, and ya seem good. put me in my place! I just wanna learn all I can)

I work on IR lasers for cutting metal. I'm a field engineer. Been in optics for 15+ years

(oh, we are talking about the roof paint, yes? if not, disregard )

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No, it's meant to reflect visible light and IR-A. Most white paint is going to have close to a similar reflective spectrum. If it were black paint then it would be absorbing vast more light. This absorbtion of light energy is going to raise the temperature of the medium regardless of the specific frequency. Don't believe me, shoot a green laser diode (with IR filter) at a piece of white paper and black paper. Which is going to burn first? The black paper because it's able to absorb more of the visible optical energy while the white paper is going to reflect it even though there is almost no IR energy.

As mentioned, there is not a lot of mid IR-B from the sun (2 uM range) and those charts were just extended out. You can see a solar spectrum chart here:

Sunlight - Wikipedia, the free encyclopedia

The black body spectrum of an HPS is going to have a spectral peak at a higher frequency than what white paint will relfect so it will absorb longer wavelength IR-C (we're talking 4-10 uM here) while mylar is going to reflect the longer IR. The black body spectrum of a HPS will be soley determined by how hot the bulb gets.

BTW, I'm an electronics engineer and I frequently have to use various photo sensors in my work.

just buy emergency mylar blankets at your local drug store.they are 100% mylar and cost is @ 1.99.