The interferometer uses a laser beam and a light detector to measure the deflection.

The light detector also lets the alien know how many hours it has been exposed to light and dark.

The two main sensors used are light detectors and electrical impedance.

Light meters or light detectors are also used in illumination.

A slightly more complex agent has two light detectors (left and right) each stimulating a wheel on the same side of the body.

These are a common type of light detector.

The light detectors may also produce information useful to scientists other than astrophysicists.

Some have pigment cells which move across the light detectors during the day, shielding them.

Camera systems used similar spinning discs and required intensely bright illumination of the subject for the light detector to work.

As to the light detector, its properties depend on temperature, voltage and the history of utilization (memory effect).