Using UV or IR as a fill light

Question

I am wanting to take some candid photos at an art workshop. I am wanting to add some fill lighting.

Unfortunately I cant use anything that will be "too distracting" for the people in the workshop. So I was wondering if I could setup some UV or infrared led lights?! Something that is visible to my camera(film) but not the humans

Can I use UV or infrared lights as fill lights?

What considerations do I need to take into account when using UV/IR as a fill lights?

Answer 1

Theoretically, yes. But it will be difficult to achieve desirable results and comes with many potential risks and gotchas.

Full disclosure, I've never tried this, but based on the somewhat limited work I've done with UV and IR films, some things to consider:

1. Ultraviolet is probably not the best choice, the higher energy light will be absorbed by melanin and scar tissue, increasing the contrast as a result. Basically, it will not have the desired illuminating effect on people with darker skin, and highlight freckles and imperfections on those with lighter skin.
2. Infrared light has the opposite problem, making melanin or scar tissue nearly invisible. It also is easily absorbed by eye tissue, potentially making them look dark in comparison to the brighter skin.
3. In either case, the contrast between the areas lit by visible light and the IR or UV will have very different visual qualities. The look will vary greatly from person to person and the two areas may not blend well.
4. Infrared light has less energy than visible light, so unless the film is engineered to be sensitive to it, it can require a lot more of it to balance out the exposure. Even if it does work, you'll probably be limited to black and white film because IR is not going to provide a fill light that matches the color of what its illuminating. Generally color films sensitive to the VNIR range look oddly otherworldly with a pinkish hue from the IR exposure.
5. Your best bet is probably to find a full spectrum black-and-white film and use a UV filter in order to block that part of the spectrum. These are usually used in forensic or scientific situations, but may be exceedingly difficult to find because most situations now use digital cameras with modified sensors.

All you can really do is procure the appropriate film stock and give it a try. I doubt you'll find the results what you expect them to be, but you may still like them. Nothing ventured and all that jazz.

That being said, it takes very little power to provide fill for a dark scene. High ISO film and a strobe at a very low power setting might serve you better. A flash set that low won't likely be considered "too distracting".

Answer 2

You may get light with UV or IR, but you won't get colors. That may be OK for black-and-white photos. To get accurate R, G, B colors, you need a source light that contains red, green and blue wavelength (this is the case for "white light").

Answer 3

More problems:

Most lenses focus IR and UV in different places than visible light. (Why there are IR focus marks on old lenses)

Modern lenses tend to have some UV blocking in the coating.

Modern room lighting solutions throw very little IR/UV.

And, um, film? There are things where film is still a fun option.... but digital has such an overwhelming advantage in low light I can't imagine wanting to use film there. Full frame sensor, fast stabilized lens (Canon 35/2 IS maybe) and you can shoot in crazy darkness.