Cut off the top flaps on the top of your large cardboard box using a utility knife. Ensure that the bottom of the box is completely intact and secured with masking tape.
Line the inside of the box with white construction paper. For best results, cut the construction paper so that each piece fits completely over the inside panels of the box. Attach the paper using masking tape.
Hold the underside of the box centered against the front of your light stand's lamp housing, or the metal casing which surrounds the light bulb.
Trace around the circumference of the housing with a pencil. Once finished, a circle the size of the housing's circumference should appear in the middle of the box's underside.
Cut out the circle using a utility knife.
Drape two to three sheets of white tissue paper over the open top of the cardboard box. Pull the paper taught and secure it to the outside of the box using masking tape.
Place the hole you cut over the top of your light stand's lamp housing. Gently push down on the box until it fits snugly over the housing.
Turn on your lamp to test the effect of the lightbox. For greater diffusion and softer light, add several more sheets of tissue paper to the top of the box.