You light box is fine. Mine is just a cardboard box with the sides and top cut out and white trash bag taped over the holes.

Fluorescent bulbs are not very hot. If you need more light, try 50 or 100 watt 'daylight' flourescents. You can use room light to set up and just turn them on for the shots.

I don't think the zoomed image is any darker, look at the label. I think the blue-white to darker blue-white background is a white balance problem.

To give us more to work with, what DSLR and lens(es)? What post processing software do you have?

TF