I remember learning that when I open a fridge door on Shabbat and the light turns on that would be under the category of melacha shein tzricha legufo?
Can anyone please provide a source?
By the way -- melacha is feminine, and therefore the expression is *melacha she'einah tzricha legufah" -- "work not needed for its own self." And it doesn't appear to qualify as such.
The light bulb appears instead to be a classic case of psik reisha -- "I just want to take the head off this chicken, I don't necessarily want the side effect of the chicken dying." Thus -- "I just want to open the door, not necessarily the side effect of the light turning on.
Melacha she'eina tzricha legufah means I intend to do a melacha action, but for a totally different purpose than its normal (or as-in-the-Mishkan) one. A normal purpose of burning is to generate light and heat; so when I flick on a light switch intending to make a tungsten filament get hot and light up the room, that is a normal use case of hav'arah. (An einah tzricha legufa case would be burning a promissory note to dispose of it after the debt's been paid. Constructive, but not the "normal" use of burning.)
Therefore pretty much anytime one turns on an incandescent bulb, it's tzricha legufah. The arguments instead hinge on whether my actions (opening the door) connect to the melacha (heating metal to produce light).