The light sensor on the Circuit Playground Express is in the upper left corner above push button A marked with an eye and A8.
The light sensor returns a relative value, not a calibrated reading. The light sensor is very good at reading values and having values compared, such that a determination is made if the environment is darker (less light detected) or lighter (more light detected).
The next pages will show you how to use the light sensor both in MakeCode and CircuitPython.
