I submit that the greatest opening to a written work in the English language isn't even from a novel

Well then if it's me I print out this picture and put it up over the light switch with an aggressive quantity of duct tape, maybe even with a bunch of glitter behind it if were improperly removed

I don't know if you're allowed to make modifications to your lab space but there are several options for keyed light switch locks like below. Put a note on the coverplate instructing them to find lab personnel to open the door

Someone likes their halogens

Polycarbonate be like

If you're a scientist you get to play with a fancy spin art toy and call it work: A rainbow of fluorescent solids on a spin coat chuck for #fluorescencefriday