I'm looking for a small light for an art project I am working on. I'm assuming LED would be the way to go for high intensity & low heat. I need one small enough to fit inside someone's mouth (I am assuming that a small ziplock will deal with any moisture issues). I don't know if you are in the business of selling one-off small lights, but if not I'm hoping you can point me in the direction of someone that does.
LEDs often produce a high intensity light, and if used correctly, will produce less heat when compared to other lighting technologies. Even though the heat can be less, it can still be significant, and if the LED is used in a certain way, it can produce even more heat than you might expect! Many designers will increase the drive current expecting to achieve a higher light output from the LED. What they might not have considered carefully is how the increased drive current will have a detrimental affect on energy efficiency caused by excess heat dissipation.
I would be more concerned about protecting the human from the electronics, rather than protecting the electronics from the human. If the LED will be located within the mouth, you want to be sure the circuity does not contain any hazardous materials. To start, make sure the LED is RoHS complaint, which basically means it should not contain lead. You should check this out for other electronics and the circuit board as well. The problem area may be your battery, as it may be difficult to find one that does not contain hazardous materials. You may want to focus heavily on the isolation barrier, that would provide protection for the human while placed within the mount, and also if accidentally swallowed. A plastic bag may easily rip open, so this may not be the best solution here.
One LED package size I would recommend is the standard 1206 surface mount. As the name implies, its only 0.120" by 0.060", and offered by a wide variety of LED manufactures. If that is not small enough, you can try a 0805, which is just a bit smaller than the 1206. No matter which package size you choose, these LEDs should not provide much heat, and many are extremely bright for their size! Expect a to see a wide beam angle from the LED, between 100 to 140 degrees, as these values are common for many surface mount packages.