Lighting - Photography - Beneath the Waves

Lighting

Warning: this article describes working with sources of ultraviolet light. If you have any interest in doing this on your own, please read the article on Ultraviolet Safety to familiarize yourself with the hazards, including the potential to cause permanent blindness or other injury.

If you take up multispectral photography as a hobby, sooner or later you will discover that "available light" in the bands you are shooting is often less than ideal. In particular, fluorescent lights emit virtually nothing outside of the human-visible spectrum (which is one of the reasons they use so much less electricity than incandescent bulbs).

Shooting outdoors on a sunny day is a great option, if it works for what you want to take pictures of. Indoor photography in a controlled environment has many advantages, and if you want to go that route, sooner or later you'll need to investigate artificial sources of IR and UV light.

Halogen Lamps

A $30 halogen worklight is currently my main tool for indoor photography. In its normal state, it emits quite a bit of infrared, and even a little ultraviolet. If the glass filter over the bulbs is removed (on mine, it flips down after a screw is removed), it emits enough UV to be very useful for ultraviolet-A photography, as well as being a hazard to eyes and skin (see Ultraviolet Safety).

Black Lights

"Black lights" (the fluorescent tubes which appear violet to our eyes and cause certain materials to glow) are excellent sources of both ultraviolet-A and near infrared light. They are also generally safe to use without eye protection, unlike most other UV sources.

Because they emit very little human-visible light, a second light source must be used in order to capture the visible-light version of a shot (if the photographer has an interest in doing so, of course). On the other hand, they can also be used for visible-light photography of materials which fluoresce under ultraviolet-A light, which broad-spectrum lighting cannot.

For this type of lighting, I use a pair of 15 watt tubes in a metal "swing arm" desk lamp to make it easy to position in relation to the subject of the photo.

When purchasing black lights, my recommendation is to look for fluorescent tubes or bulbs. There are incandescent black lights, but they get extremely hot and won't put out as much ultraviolet-A light.

If you are interested in photographing fluorescence effects, especially with a camera converted for multispectral use, be prepared to add more filters to the front of your camera to block the near infrared light (both from this type of tube and the scientific variety of light described below). My standard "normal camera" filter - the LDP CC1 - still lets through enough near infrared that a pink tint is added to the entire image when using this type of lighting.

Germicidal (UV-C) Lights

Germicidal Lamps are essentially fluorescent tubes, but without the phosphor lining which downconverts short-wave (ultraviolet-C) light to light that we can see. The tubes are also generally made out of fused silica/quartz to maximize transmission.

To human eyes, or a conventional camera, the light given off by these tubes is an eerie pale blue colour, but don't be fooled - they throw off an enormous amount of short-wave ultraviolet light, and are extremely hazardous if the proper precautions aren't taken.

This type of lamp on its own will cause fluorescence in material that responds to short-wave ultraviolet (mostly minerals of various types), but because of the ultraviolet-A and human-visible "contamination", the results are very washed-out compared to what can be obtained with a filtered source (see below).

I have a "swing-arm" desk lamp that I converted to use 13 watt UV-C tubes (by replacing the tube socket), but I do not recommend that others do the same in most cases. There are better (and less dangerous) sources for the ultraviolet-A and near infrared it emits, and as previously mentioned any fluorescence it causes is washed out by the other bands.

Scientific Ultraviolet Lights

There are many manufacturers of dual-mode "long-wave" (ultraviolet-A)/"short-wave" (ultraviolet-C) lights for scientific purposes. Geologists use them to examine fluorescence in minerals (which can appear radically different under the two types of ultraviolet light). Other scientists may use them with fluorescent stains in the lab.

This type of light is essentially two tubes (one being "black light"/ultraviolet-A, and the other germicidal/ultraviolet-C) mounted in a case behind an ultraviolet-bandpass filter, with a switch to toggle between them. The filter is the hard/expensive part to obtain (except by buying one of these lights), so it would be extremely difficult to "DIY" one. By filtering out the non-ultraviolet "contamination", a light source which is very useful for causing fluorescence is produced.

Even though these lights appear very dim, it is just as important to wear proper safety gear when using them!

This type of light is very easy to find second-hand. However, be warned that ultraviolet-bandpass filters, when used in this type of application, are vulnerable to a condition called "solarization". Over time, the exposure to UV-C light causes the filter to become opaque to that band, so even when the UV-C light is on, very little of that light may be emitted from the device. The lifetime for modern ultraviolet-bandpass filters is measured in thousands of hours, so it is certainly possible to get a used light which is still fully functional, but that amount of usage is certainly not unheard of in a lab-type environment. It is very expensive to replace the filter.

I have only seen a handful of scientific lights that have the ability to produce ultraviolet-B. I assume this means that there is very little use for that band in terms of fluorescence, but if anyone knows for sure, please fill me in.

Flashes

I currently don't have an IR or UV flash, and don't use a regular flash unless I absolutely have to. I prefer available light, with "hot lighting" my second choice. That having been said, some applications require a flash. The main factory choice here is Nikon's SB-140, which is even harder to find and more expensive than the UV-Nikkor lens. As a possible alternative, Shane Elen of Beyond Visible offers standard Nikon SB-14 flashes modified to perform similar functions. They're still a bit pricey for hobby use, but would be a bargain for professionals.

Related Articles:
Cameras
Lenses
Filters
Other Tools
Ultraviolet Safety