You are dissipating ten or twenty watts, most of that going to heat (incandescent bulbs of any type are not really very efficient).

Some newer lights have less heat transfer, but the penalty is the lights need to be thicker and stick down more.

Most of the folks I know just do not put anything heat sensitive directly on the bottom of the cabinet.

Thank you so much, brickeyee. That is very helpful. So, one more thing... Is there any reason to be concerned that over time, the heat will warp or cause any other problem with the cabinet wood frame, wood (or wood veneer)doors, or trim?

You could remove the light and mount a sheet of copper or aluminum over the spot where the light goes, then replace the light. Now the metal sheet will act as a radiator or diffuser for the light, less heat will get into the cabinet. You can also leave an air gap between the fixture and the cabinet and some heat will be carried away by convection.

Ken mce - Thank you so much for your very helpful response. I really appreciate it.

it is true that any surface amount of foil will help to _spread_ _out_ the heat and to reflect a little bit of it downwards. Perhaps it may not make enough difference to be feel-able when you use your fingertips as thermometers by touching the wood above the hot spot, but it will certainly be doing the job of spreading the heat over a wider area, so your wood glue cabinet material will be less stressed at that one spot where the light is. Without overthinking it, you could loosen the screw on a fixture, slide some tin foil between the light and the cabinet, tighten the screw, and see if that one light fixtures' heat is a bit less intense when you compare it to the others. The pan material that readymade meals come in is thin enough to fit, and also a lot thicker than aluminum foil.

"... watts, most of that going to heat (incandescent bulbs of any type are not really very efficient)..."
"Heat output ... power input, how many watts..."
"Watts are the power consumed. All power turns into heat ... "

Here is a link that might be useful: f/u to xenon lights getting hot

Thanks Davidro1 - that is a helpful suggestion.

Heat rises. You are making a lot of heat. It is going to heat up your cabinets, that's all there is to it. Even F32T8 fluorescents heat up the cabinets a bit (though smaller ones are little trouble).

Yes, it can melt chocolate. It also degrades spices and herbs stored in the cabinets.

The heat is highest on the bottom shelves, of course, but the entire cabinet interior becomes warmer than ambient temperature.

You could try mounting the lights on 1/2" or so standoffs, and even consider adding small DC brushless fans to circulate air through the gap. Or just replace them with lights that have decent efficacy, instead of being heaters that happen to also produce light.

"Heat rises" is false.

Heat in this situation under discussion does not rise: it goes in all directions imaginable.

Heated air rises.
Only heated air rises, in the typical household situation.
It only rises if there is other air that is cooler which can take its place when it rises.
(Heated fluids rise, also, when surrounded by fluid that allows them to rise. Since they are more lightweight when warm)

If anyone insists that heat rises, tell them to ask the sun which way it sends its heat since "heat rises". Wikipedia on heat : it is energy, which moves in all directions possible, without regard to the gravitational field of our planet. Heat = heat radiation. (Radiation is the term, but it has nothing to do with nuclear radiation.)

http://en.wikipedia.org/wiki/Heat : It is energy, and it moves through space , without looking at gravity to choose a direction. It always moves and never stays still.

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the second thing that may need to be corrected is the statement
"replace them with lights that have decent efficacy,..."
because it may be necessary to tell the OP that all lights of the incandescent family are all heaters, and the differences between them are not great.
Go with LED's or thin tube fluorescents if anyone feels the heat of an incandescent (of any type) is too much heat.

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1/2" spacing can be good to get air to take the heat away.

I strongly suggest that you switch to LED or mini fluorescent.

"Heat rises" is false.

OK, fair enough. To be correct, heated air rises.

That's germane, and it's exactly what I'm talking about. The heated bottom of the cabinet warms the air above it. That air rises to heat the remainder of the cabinet.

Go with LED's or thin tube fluorescents if anyone feels the heat of an incandescent (of any type) is too much heat.

That's precisely what I meant when I said "replace them with lights that have decent efficacy, instead of being heaters that happen to also produce light."

We don't seem to be in disagreement, David. :)