Light Box

Lighten up


A light box is a versatile learning tool that an be used to investigate many facets of light from image formation to color addition.


light box drawing

A bankers box houses a linear filament light bulb to make a Light Box.


In addition other materials will be needed for each of the activities which use the light box.


Hot melt glue the extension cord outlet strip to the center of the box lid.
Plug a bulb socket into the outlet.

Optional rugged construction
Cut the wood board to fit inside the lid of the box.
Hot melt glue the extension cord outlet strip to the center of the board.
Hot melt glue the board into the lid so that the bulb socket is centered.

Cut a rectangular hole 4 inches wide and 3 inches high in the center of one side where the box joins the lid.

Optional, you can cut a similar hole on the other side of the box to allow two groups to work with one box.

Cut two 2" square holes in the top of the box to allow air to circulate and keep the bulb cool.

Install a lamp in the socket.
Cover a tabletop with white paper,
place the lid with the lamp on the table,
cover the lamp with the box.
The bankers box will be upside down on the table.
Turn on the light and you have a light box.


Hooray for rays

Warning! the following exploration is just an outline.


Rays of light can be used to show where an image is located as well as the difference between real and virtual images.



Cut a set of 5 vertical slits 0.25 cm (1/8 inch) wide , 0.5 cm (1/4 inch) apart and 4 inches long in the 5 x 7 card

To protect the card, slide it into a report cover and then trim away the excess plastic.
To save work, you can also use the card without placing it in the plastic.

To Do and Notice/ What's Going On?

Place the light box over white paper.
Mount the card with its grid of vertical lines over the hole in the side of the box..
Turn on the bulb and notice the rays of light.
The rays of light are made by the vertical filament together with the array of vertical slits.

The rays of light all radiate out from one point, that point is the filament.
When expanding rays enter your eyes, your eyes and brain uses information on the divergence of the rays as one clue to estimate the location of the filament.

Place a cylinder of water in the rays of light.
Notice that the cylinder bends the rays of light until they come together and then spread out again. If the eye intercepts the spreading light the eye and brain perceive an image at the location from which the rays spread. That is, where they cross.
The crossing point of the rays is called the image point.
(Notice that this crossing point is not the focal point of the lens, the focal point is the place where parallel rays come together, the rays from the light box are not parallel.)

Use a piece of white paper to find the image, a line of light.
The image of the filament, will be present on the paper when it is held at the image location.

Notice that not all of the rays cross at one place, this is because the cylinder is not the exactly correct shape for a lens. The rays that do not cross at a point show that the cylinder has spherical aberration. The correct shape for a lens is an aspherical curve.

(Cover half of the rays that enter the cylinder with a red transparent colored filter and notice that the rays that come into the crossing point from the right leave it on the left.)

Notice how the image point changes as the distance from the filament to the cylinder changes. A filament-object further from the lens-cylinder makes an image closer to the cylinder.

Notice that at close distances the position of the image changes when a red or blue filter is held in front of all of the slits. (The bending of light by the cylinder called refraction is a function of the wavelength of the light. Water and plastic bend blue light more than red light so the blue image is closer to the cylinder than the red one.)

Notice that if a second identical cylinder is filled with sugar syrup the light bends more and the image is closer to the syrup filled cylinder than the water filled one.

Cylinders with larger radius bend the light less so that the image is farther from the cylinder.

Use a concave lens (or insert an empty cylinder into a square box of water). Notice how the rays that spread from the filament spread even more after they pass through the lens. The point from which they appear to spread is also an image.
When the rays actually pass through the image location it is called a real image, when they only appear to come from the location of the image then the image is called a virtual image.

The rays can be reflected from a small flat mirror. They continue to spread as if they come from a place as far behind the mirror as the filament is in front of the mirror.
This is a virtual image.

A thick sheet of mylar or a thin (3 mm) acrylic mirror, can be bent to form a mirror.
Reflect the rays from a concave mirror, they can be made to come back together to form a real image.

Reflect the rays from a convex mirror and they will spread more, making a virtual image.


The art of light box construction and use was elevated to a fine art by Chris deLatour at the Exploratorium.

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Scientific Explorations
© 1999

22 May 2000