lighting "approved for use in showers"

[augie47]

That is not what it says..........Read carefully............ It does nor say "outside of the tub" it says "WITHIN" the outside dimension"

('17) .......Luminaires located within the actual outside dimension of the bath‐ tub or shower to a height of 2.5 m (8 ft) vertically from the top of the bathtub rim or shower threshold shall be marked for damp locations, or marked for wet locations where subject to shower spray.

 

[Flicker Index]

There's the code part, but also unique environment within the shower. It could pass the safety requirements while failing real life reliability expectations. The absolute humidity load in bathroom is considerable and the amount of condensation that forms on items below the dew point is quite a bit more than something cool being brought into the house from outside.

An ordinary line voltage LED board would likely fry out from moisture droplets. A design I've seen in shower rated fixture is a fully isolated low voltage constant current LED ballast setup as a piggyback AC adapter and driving the LED elements at 0.5A at 16-20v or so. The LED elements were spaced out in a way that electrolytic galvanic corrosion won't be a problem from an exposure to vapor phase water. The entire LED ballast was encapsulated in epoxy or silicone so steam don't condense onto parts.

Ordinary light fixtures typically use non-isolated pre-fabricated hockey puck board operating at anything from 60 to 350v DC across the module and presenting over 100 volts over ground that may fail when steam condenses on it.