Is there a way to test the ambient light sensor?

I have recently had to replace my FCAM/Sensor assembly (my ear piece audio went out) and was able to use an app to test the proximity sensor but there is no such ability with the ambient light sensor. I move from a well light room to a dark room and don't notice any difference but I never really payed any attention in the past so can't really tell if this would be noticeable. Is there any way to test this? or even create a situation when where the shift in brightness should be clearly apparent?