Before we can measure planets, we work out the basic law of photometry: as the distance from the lamp increases, the detector receives less and less light.
![](https://exopla.net/wp-content/uploads/2020/01/abstgesetz_messen.jpg)
Tools:
Photometer
Lamp
Tape Measure
Procedure:
Measure the irradiance every 10 cm at distances from the lamp: ten readings between 10 and 110 cm
![](https://exopla.net/wp-content/uploads/2020/01/entflichtkurve-1024x297.png)
Result: The decline is quadratic.
![](https://exopla.net/wp-content/uploads/2020/01/tafel_abstGesLUX_white.jpg)