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The pupil size changes depending on the amount of light in the surroundings. Light levels can be measured using a light meter. Units of light are measured in lux. The higher the lux reading, the brighter the light is.

Method

1. Set up three rooms with different light levels, for example, a dimly lit room, a normally lit room and a brightly lit room, or outside.
2. Measure the light levels using a light meter and record the lux levels in a results table.
3. A person goes into the dimmest room. They stay in there for a few minutes to make sure that their eye has got used to the light levels and the pupil is staying at a constant diameter.
4. Use a digital camera to take a close-up image of the eye. DO NOT use flash as this will cause the pupil to change size.
5. The person goes to the other two rooms and steps 3-4 are repeated. The digital camera must be on exactly the same settings and used the same distance from the eye so that the images can be compared.
6. Using the images from the digital camera, the diameter of the pupil in each of the rooms can be measured using a ruler. Record your results.
7. Repeat the experiment with other people to increase the range of results collected.

Results