I would only use a sauna rated light fixture, ones for this height will have to be a filament bulb, and are often encased in glass. I would also use silicone cabling. LEDs don’t handle heat very well, and most sauna ones are only rated for lower levels.

I would use the regular sauna vapour barrier too, and I would run a heat proof silicone cable for a safe distance, rather than a PVC or rubber one.

Here’s some ideas: https://www.saunainter.com/en/sauna-lighting/sauna-lamps/?page=2

Also: https://www.saunainter.com/en/sauna-building/electric-sauna-cables/silicone-sheathed-cable-sihf-3x1-5mm--/sk315/ (might be slightly overspecced in terms of thickness for a light)

All light fixtures inside the hot room should be sauna rated. I don’t know how that works outside Finland, but I’m sure any ceramic lamp base would be better than a plastic one. And please don’t forget about the IP rating.

Do you have details about the exact material? “Plastic” doesn’t really say much - plus you don’t really have to worry about the melting point, but the glass transition temperature. That’s the temperature at which it loses stability, which can be more than 100°C away from its melting point. Depending on the type of plastic and additives you’re looking at a range of roughly 50°C to 400°C for the glass transition temperature - and I’m assuming that kind of part needs to have a relatively high rating for fire safety reasons. So, try to get the datasheet for that thing.

This is the location of the light to the heater, btw.

Thanks all. I shared this with the electricians and they replaced the plastic backing with some metal product. I’ll also make sure they’re using a sauna rated lighting product.