How to Build a Ray Box

Find the center of the short side of the shoe box with a ruler or measuring tape.

Cut a slit from the open side of the box toward the center that measures about 1/32 inch wide by 1 1/2 to 2 inches long. Keep the cut as clean as possible.

Cut a round hole in the other short side of the box, just large enough to slide the shaft of the flashlight through.

Slide the flashlight into place from the inside of the box. Secure the flashlight in place from the outside with duct tape. Make sure the duct tape covers the hole completely to keep outside light sources out and the flashlight beam inside.

Lay the box on a table with the bottom side up, so that the slit touches the table surface and the flashlight sticks out the back of the box.

Place a piece of white paper flat on the table in front of the slit side of the box, overlapping it slightly under the lip of the box on the side with the slit.

Turn off the lights in the room and close the curtains or shades to block out any extra light.

Turn on the flashlight and check if there is a straight ray of light emerging through the slit. If the light is spread out, the slit is too large and you need to try again with a new box.

Tape a piece of white paper to the wall next to the box, with the slit end facing the paper.

Stand the prism on its end in front of the beam of light. Adjust its position so it casts a rainbow on the white paper taped to the wall.