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Hi. I know of the commercially available "battery-less" flashlights
that use either squeezing or shaking mechanisms to generate
electricity. I was wondering, however, whether I can create one that
uses the difference of temperature between the hand and the room
temperature. I propose to use a LTD Stirling engine to drive a magnet
inside a coil of wires to generate electricity. My question is, can a
carefully constructed Stirling engine with the size of this:
(cylindrical, 10cm in diameter, and no longer than 30m in lenght), be
powerful enough to generate electricity enough for 1 or 2 high output
LEDs to light up?
If it can, can someone guide me to building this Stirling engine? I'm
hoping to get an university professor to help me and I can access the
school's metalshop's lathe and welding machines and grinders and
others. So please respond. Thank you very much.

LTD Stirling engines that run on the temperature difference between your hand and room temperature have just about enough to overcome friction.
The Stirling Flashlight would be a dismal (dark) failure.

I have to say that I disagree about them being a dismal prospect. I recently watched a video on youtube from a french website where a man built a LTD using a diaphram piston that was running off of the temperature difference from the evaporation of water, and it had a small alternator he made that was making some LED's flash. For just charging some capacitors or light batteries, it would work fine..of course you would have to hold on to it for quite a while, but hey, you aren't having to do any work at all.

Now, if you want the Stirling engine to power it directly, indefinitely, then I would agree it is a hopeless endeavor, unless researchers can come up with a OLED that is nearly 100% efficient in converting electricity into light.

Now, given that this post is about 2 years old...no one probably cares, but I've toyed with this idea as well, and I think it could work...however impractical it may be.