The power button for the Light and Color Sensor also turns on the white LED. In order to turn on the light, turn the sensor on by pressing the power button, waiting until the Bluetooth LED begins flashing (5 seconds) and then pressing the power button again. You can toggle the light on and off with the power button.
The power button is non-responsive for the first 5 seconds after initially turning the sensor on. The power button is disabled during this initial period.