I would suggest either the trim or fixture. Get some inspiration from existing hoods in your local kitchen / appliance showroom.

Thanks; maybe I should clarify that by "fixture" I mean the recessed can, which is typically sold separately from the trim. So it's a question of what characteristics to require in the can, in the trim, and in the bulb.

Sadly, I don't think the local showroom will let me dismantle their hoods to figure out where the lighting components are sourced. I'm also mainly seeing halogens in that application.

Grease is more of a problem than moisture in a range hood.

Have you looked at Fujioh for inspiration? They also sell inserts.
http://www.fujioh.com/

They use standard E26 sockets. Since the lights are mounted in the front rather than at the rear, the lights are open.

Like brickeyee said, moisture is not so much of a problem.

In any case, most of the moisture / grease laden air is supposed to be sucked into the hood and trapped by the baffles/ mesh filters.

Sorry. I obviously haven't been very clear.

1. I am using LEDs, not halogens. I think the difference matters. Some LED lamps will fit some sockets that some halogen lamps use, but interoperability is not total. Moreover LED lamps made to provide a broader beam (say 40 degrees) typically have multiple emitters in a sort of cone shape -- it's a different kind of lamp from those tiny hot halogen bulbs with a reflector.

2. I really am serious about mounting them behind a gasket-sealed lens, at minimum, both to keep moisture out and to provide a surface that is easy to clean.

I don't want to argue about what are for me minimum safety and cleanliness standards.

My question was how to *achieve* those standards, given that the data on lighting hardware is pretty opaque.