The white-light LED in the Optics Expansion Kit (OEK) performs several functions. It is most often used to illuminate the luminous light source for imaging experiments.
When used for the inverse square experiment, it is important to let the LED come to thermal equilibrium before taking data. This takes 15 minutes or more. During this time the light intensity drops by about 20%. If an inverse-square experiment is done slowly during this warmup time, the results will be off due to the intensity of the source changing during the experiment.
We suggest letting the LED stabilize for about 20 minutes before performing this particular experiment.