In Physics,there is a topic by the name of "Photometry" (under the subject Light).In this topic the Illuminating Powers of two Illuminating Sources are compared.

One intersting point. Do not you find that the following Sher of "Daag"deals  with Photometry?

 Rukhe Roshan ke Aage Shamaa Rakh Kar Yeh Kahate Hain.  

 Udhar Jata  Hai Dekhen , ya Idhar Parwana Aata Hai.