This involves vision, but not for the purpose of illumination - working on a fence after dark, I set one of my lights on the second to last fence post so I could line up it with the shadow of the last fence post, in order to help me get my next fence post in line.
I have also on occasion used my higher power lights to "x-ray" plastic items, such as to get an idea how they're held together
Good ones.
I've done both of those with various light sources in the past, posts with work lights, and most commonly I'll "X ray" bic lighters to see how the fuel levels are, for accuracy beyond shaking and listening.
Laying a light on the floor, shining sideways is a favorite for finding tiny objects by their shadows, good for follow up with cleaning up broken glass too, or along a wall if you want to see all the flaws in your drywall and painting.
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