I am making a light box and need some advice

Ok, I decided to build a light box this week as I have unexpectedly found myself with time on my hands. The problem is I know the wife will complain as it will be in the way of her 3 fishtanks, so I plan on putting it into my loft if it is not too cold. Obviously my loft is unheated so it will never be as warm as the rest of the house, but would it be too cold for a light box?

Also another thing, is making the inside of it reflective. Should I use tin foil, or paint it with white paint? The problem with tin foil would be the earthing, so if white paint is up to the job I will go with that.

I will post a pic once it's built

 

Hi David. I have thought about such a box - but have never done anything. I am sure many of us would be interested in how it works out. My own thoughts are :-

1) Plants will grow in the cold with low levels of light, so any improvement will be a step foreward. It doesn't have to be perfect.
2) Ideally you need very high levels of light to get anywhere close to summer sunshine. I have seen it recommended that the lights should be only 2 inches above the top of the plants, with a mechanism to raise the lights as the plants grow. But this was not inside a box.
3) Ideally I would use mirrored glass, but the next best thing would be aluminium foil. A mirror would be your first choice when shaving, aluminium foil might just work, but a white wall would not.
4) If you can keep the light reflecting within the box, the light level can be increased a lot. In theory, if you had perfectly reflecting surfaces, you could have an almost infinitetly high light intensity from a small bulb, because the light would just go round and round and the level would build up. In practice even a shiny surface will absord some light. Think of aluminium foil as light insulation in the same way as you have heat insulation.
5) I don't see a problem with earthing. I don't see why the power should come into contact with the foil. If you really were troubled you could earth it to a water pipe just using a big jubilee clip - there should be plenty of pipes in the loft.
6) You can't of course use (ordinary) incandescent bulbs, as 90% is heat and only 10% light. With a fluorescent tube, you are closer to 80% light and 20% heat. You can get special tubes, but they are expensive, and I believe that you could use ordinary long lift bulbs. A couple of 20 watt bulbs in a reflective box could give a high light level. That's the equivalent to 200 watts (of ordinary bulbs) but if your box has sufficiently good light insulation, that might double it or even more. You could measure it with a light meter.
7) I don't think the lack of heat need be a problem. If you put 40 watts of power into a very well heat insulated box, it will generate quite a temperature. The plants themselves will use a tiny amount of the light and turn it into chlorophyll, but all the rest of the light will ultimately be absorbed by the sides and turned into heat. And if the heat cannot escape it might even get too hot. Check with a max/min thermometer.
8) In summary I would want a box that was extremely well insulated for both heat and light. But you may need a little ventilation to prevent a fire hazard, and of course you have got to let the carbon dioxide get in .

There is a growing under lights forum here http://forums.gardenweb.com/forums/lights/

 

I meant to add that the lights need to be on a time switch, to simulate nighttime.