GroundBound 's advice on fixing a dodgy light - "A quick tap with the heel of my hand" - reminds me of the last time I did that.
The quick tap was followed by an even quicker trip to A&E to get my slashed wrist sewn back together before I ran out of blood. I'm now left with a beautiful scar that raises eyebrows whenever I get my medical renewed ("are you sure you don't have any suicidal tendencies?"), and a healthy respect for the effects of broken glass.
Hit it with your shoe instead. It's more stylish, and a lot safer.