Lights for steam shower are one of the few components where getting it wrong is a safety problem rather than an inconvenience. A steam enclosure is a hot, saturated, sealed box with condensate running down every surface, and an ordinary bathroom downlight is not built for it.
The rating you need
A steam enclosure is treated as the wettest zone in a bathroom, so a luminaire needs a high ingress protection rating, a gasketed lens and a body that tolerates both the heat and continuous condensation. Steam-rated fittings are sold as such. A standard shower downlight is rated for spray, which is a different and much easier condition.
Where it can go
Follow the maker's zones: fittings in the ceiling of the enclosure are the most exposed and need the highest rating, and anything in a wall below head height is in the wettest, hottest air. Keep every driver, transformer and junction outside the enclosure, in a space that can be reached, because that is what actually fails.
Why fibre optic keeps being chosen
Fibre optic puts the light source and all the electronics completely outside the enclosure and brings only a glass or acrylic fibre through the wall. Nothing electrical is in the wet zone at all, which sidesteps the whole problem. It costs more and it is what higher end steam installations use for exactly this reason.
The rest of the specification
A low voltage supply protected by a residual current device, installed by a licensed electrician to the bathroom zone rules. Warm color temperature, because a steam room at daylight white is unpleasant. And a switch outside the enclosure, always: a control inside a sealed steam box is a fault waiting to happen.
Questions people ask about lights for steam shower
Can I use a normal bathroom downlight?
No. Shower fittings are rated for spray; a steam enclosure is saturated and hot, which is a different and harder condition.
Why is fibre optic popular here?
It keeps the light source and all electronics outside the enclosure. Nothing electrical is in the wet zone at all.
Where does the switch go?
Outside the enclosure. A control inside a sealed steam box is a fault waiting to happen.