I never could figure out why people make light boxes.
No air circulation or they have to add fans or whatever to regulate heat.
Get a grow shelf and mount shop lights both vertically and horizontally around your plants.
Extra light makes tight plants that branch out earlier.
Mylar and white paint don't add that much more reflected light and are a hassle to deal with especially if you folier feed.They get dirty...reflect less light.
I use Fluoros and am building LED panels.
They (LEDs)will be on 4 sides of my plants in about 11 wavelengths of 420nm to 680nm,red and blue.
Most LEDs I use are 100+ lumen each.
Stars I use are 35-190 lumens each-3 16X16 panels up top,3 in back and 1 on either side.
Mylar in front so I can water etc.
Same thing with Fluros.
Each Star LED panel puts out about 3000+ lumens at the source-24,000Lumens of totally plant usable light at the source.
Even if you cut that in quarters due to lumin loss , as the distance away increases,it's still way more lumens of plant usable light from mostly any other source I know of.
10mm LEDs are on 12X7in. panels at about 125 LEDs per Panel at an average of 109 lumens each LED.
I get them in more plant usable wave lengths than stars with more Lumens for the price each than stars.
Don't need a LED driver,just a voltage regulator or an accurate power supply that doesn't fluctuate and resistors.
10mm LEDs are way more forgiving than stars and cheeper in general.
A 7X12 panel puts out something like 13.000 lumens at the source of plant usable light.
All peppers need are 2000Lumens of non specific , plant usable light to do great under a combination of cool white and warm white fluoro light.
I only know pepper growing light needs.
Pot or whatever probably has different light needs.
Info from non pepper sites doesn't necessarily work on peppers only.
I only grow Chile's,Nothing else.
So don't use my lighting suggestions for your eggplants and other stuff.
Some plants are light wave length specific if the stuff I read on the net is true-I doubt a lot of it.
Stuff that is popular,given as facts , is often wrong when it comes down to reality.
One that really sucks is peppers won't bud under fluoros.
They will easily bud and fruit under a mix of warm and cool Fluoros.
My biggest peeve is using Watts as a measure of Lumens...
Idiots buying snake oil think they can't use LEDs for growing plants because they baught a gazillion watt panel that put out only 100 lumens and thaught a gazillion watts meant something more than how fast your meter spins when they are turned on.
My homemade panels actually use 9-12 watts and put out +/- the lumens I listed above-at the source of mostly plant usable light.
A 660nm LED only puts out MOSTLY 660nm. wavelength not all 660nm but still in the ballpark as far as plant usable wavelengths.
Some LEDs put out higher or lower wave lengths at different voltages,allowing you to cover more of the plant specific wave lengths.
Same with cool or warm Fluoros.
For me a combination of any fluoro that puts out from 5000K to 6500K works great.
Most put out 2500-3500 Lumens depending on the bulb-T12,T10 etc.
T10's work better for me than T12 Fluros.
Shop lights are cheep in general.
Spend the $ you'd spend on a light box , mylar and a fan or whatever on a couple shop lights.
I'm assuming you are growing more than a couple plants at a time.
I only did 100 or so starts this year.I usually start about 300-400 starts a season.
Mites suck.
I think I'm great at raising them...Want some?
They probably would love a box full of sprouts that is about 80 degrees F.