I'm planning to print up a bunch of brackets to mount LED shop lights (very similar to these) to the ceiling in my garage. My plan is to use an upside-down "U" shape bracket that screws into a joist/drywall anchor in the middle and then sort of clips around the sides of the metal frame.
Maybe filament type doesn't matter much here, but I'd rather not come out to one of the lights having fallen on my car if I can help it 😅
I think the main considerations are just temperature and stiffness. It can get up to about 85F in the garage on the hottest summer days, and probably a few degrees warmer by the ceiling. The lamps are cheap LED tubes, so the metal housing only gets slightly warm to the touch (say 90-100F or so). I know PLA is a bit stiffer at room temp, but I'm worried it might soften too much at the worst case of warm temperatures.
Any thoughts on PLA vs PETG for this situation?
First of all, PLA is not brittle at all. I don't understand why people use this word. Glass is brittle, PLA is not. It does have lower impact resistance than PETG, but the difference is not that big. Also, bendy part is as useful as a snapped part in every application that requires strength. Tensile strength and flexural strength is usually more important in most applications and PLA excels in those.
If impact resistance is important to you, you can try BASF PRO1 PLA, which absorbs much higher impact forces than any regular PETG.
Glass transition temperature for PLA is 60C. It does NOT warp or bend at temperatures below 60C. It's just physically impossible. But yeah, 60C is quite a low temperature for many applications. Glass transition temperature of PETG is just 81C. While it's higher than PLA it is still not suitable for anything which can reach boiling water temps.
If both strength and temperature resistance are important, then the obvious choice is ASA. PETG's only benefit is that you can buy certified food safe PETG filament easily and cheaply. Otherwise PETG is pretty much useless for all intents and purposes.
In the interests of avoiding pointless semantic arguments, you can probably safely assume that in any discussion of the relative merits of materials, the word “more” precedes any adjective describing said material’s properties. For example: PLA is more brittle than PETG.
I don’t agree. There are many application where a bending failure mode is much more desirable than snapping. OP’s situation, for example. Pretty sure they’d much rather they were alerted to a problem because their lights were pointing in the wrong direction than smashed on the floor.
The extra temperature resistance of PETG compared to PLA might not be a big number on paper, but it makes it suitable for many things PLA isn’t. Things for use in a car, for example, are common to see problems when printed in PLA (you can find tons of pictures of PLA phone holders melted in the sun). PETG isn’t immune but will almost always fare better in any situation where there might be heat. For example, an LED light fitting, like OP's situation.
Anyway. Do we really have to fanboy materials?