"No concept can exist without its opposite" ... or so it is philosophically pondered.
In concrete terms, light is the natural agent that stimulates sight and makes things visible. On the other hand, darkness is the partial or total absence of light.
If I had a third hand, I'd state that shadow is a dark area or shape produced by a body coming between rays of light and a surface. And then there is contrast, the state of being strikingly different from something else, typically something in juxtaposition or close association.
Octopus that I try to be at times, three more things ... transparent, translucent and opaque.
A transparent object or substance allows light to pass through ... clear glass, water, air (to an extent), a translucent object/substance allows some light to pass through ... like stained glass. And finally, an object absorbs some light, reflects some but allows none to be transmitted through.
I contend that awareness of these phenomena will make any photographer more competent than he/she was prior to the time they were exploited by that photographer!
The images and their captions will hopefully be helpful to those who like to take fireworks photos.
© All Rights Reserved/Photos and Text/A. Macarthur