you could always use a few cfls, u know the energy saving ones.
You need these:
Cardboard box, about 4 foot wide, 1 foot deep and 1 foot high
Tape
Foil
3 12cm computer fans
Light pendants or similar light fitting
CFLs, any wattage really, but the higher the better
String
4 4-foot wooden beams
Get the cardboard box and fold up one of the ends. do it the way its meant to be folded and tape it, so that it doesnt leave any gaps where its been bent.
Line the bottom and sides with foil.
Stand the box on a short side so the box is now 4 foot high. insert the wooden beams into the corners- this will provide support. Glue them in place.
Now punch some holes large enough for a power cable through the top of the box. feed some wire through. this will get the power to your lights. Next punch a few smaller holes through the top about an inch from the other holes, large enough to fit the string through.
Attach the lamps to the power, and string up the pendants.
For doors we want to use just the main flaps left on the opening, not the 2 small ones. Cut these off to 1 inch from the side of the box, and glue these baby flaps in a 'closed', upright position. This is to stop light leaking through the top and bottom of the box.
Using some of the excess cardboard, cut a few 2x2 inch pieces, and punch a hole through them large enough to fit string through. feed the string from your lights through the hole, then wind some string around them and sit them on top of your box. this will make your light movable. using some more of the excess, cut long thin pieces (bout 1 inch wide) to fit on one of the doors.
Stick it on one door where both doors meet. stick it half on the door, half off, all the way up. this will stop light from coming through from inbetween the doors.
Next, us a pen to draw around one of the fans. Draw one at the bottom corner on one of the side, and one in the top corners on the side. this will be ventilation. put the fan in with glue or silicone, or anything you can. make sure the bottom one draws air in, and the top one pushs it out.
Ataach on magent to the inside of both flaps, wher the door with out the seal is going to close. this is cos you will close this door last. attach another set of magnets to the outside of the door. This will hold the door in place, and not push it out.
Position the last fan where it can blow mildly over the plant, and voila. all done..sorta!