Ultraviolet-induced fluorescence (UVIF) occurs when molecules in an object are excited (energized) by high-energy ultraviolet wavelengths (from our UV flashlight) and as a result, emit longer wavelengths in the visible portion of the spectrum (red, green, and blue). These emitted longer wavelengths are what we are photographing.
Warning: Ultraviolet (UV) light can cause serious damage to the eyes and skin. Always wear appropriate UV protection when using UV lights. Never look directly at a UV light source.
First, find a completely dark location where you can set up a camera and tripod. This area should have a desk or bench to support the item being photographed.
Order a UV flashlight. If you want to record images like the ones I have created, your flashlight should emit UV light at 365 nanometers (nm). The UV flashlight I used was a simple $22 mini flashlight I purchased on Amazon (the Darkbeam 365nm Mini Handheld Torch).
Pick up a small LED flashlight that emits light at about 5500 K (normal daylight). This flashlight will be used to create your natural color reference images.
Once your UV flashlight arrives, wait until the evening or night and go searching for items that fluoresce with 365 nm UV light. Look at flowers, plants, rocks, or lichen in your area to see what looks interesting. Some man-made items also fluoresce so take a look around your house and see what you can find.
Collect a few items and bring them into your dark area.
Set up your camera and tripod near the table or bench and place one item on a clean black surface. I used a black piece of foam-core but anything that won’t fluoresce will work.
Turn off the room lights and illuminate the object with your UV flashlight to see what parts are interesting to photograph. Turn the room lights back on.
Position the item, camera, and lens so the area of interest fills the frame. I used a 100 mm macro lens on my DSLR which worked quite well.
Turn off your camera’s Auto Focus system and focus on the object manually (your camera won’t focus in the dark).
Set your camera’s White Balance to the Daylight setting or 5500 K (do not use Auto White Balance).
Set your camera to record RAW images if it is capable of doing so; this will give you the best image quality possible. If your camera can only record JPG images, set it to the highest quality setting.
Set your camera to record images in Manual exposure mode.
Set your lens aperture to a value that will give you the amount of depth of field you need. I used a setting of F22 for increased depth of field but you can choose any value you wish. The higher the F value, the longer the exposure will be.
Set the shutter speed to 20 seconds. This is a good starting point but you can change it once you become familiar with how long the exposures will need to be. You can leave the shutter open and then control the exposure by adjusting the length of time you have the flashlight turned on.
Set your camera’s ISO setting to 1000. This is a good starting point but you can change it once you become familiar with the procedure.
Set up the camera so it shows the recorded image’s histogram. Images often appear much brighter in the camera’s display when you are in a dark room so the histogram will show you if you actually have a good exposure.
Use a cable switch to trigger the shutter or use the camera’s self-timer and set it for a 2-second delay.
Check to make sure your object is still in frame and in focus.
Turn off the room lights and trigger the camera.
Once the shutter is open, turn on the daylight-balanced flashlight and illuminate the object from different angles. I use a smooth arc motion around the front of the object so as to decrease the likelihood of shadows in the object. Note how long you illuminate the object and from what distance. You can alter both illumination time and distance to increase or decrease the image exposure.
Check the image histogram to determine if you need to increase or decrease the exposure.
Record another image making changes in your lighting technique. It will take a few tries to create a good exposure so be patient and try different distances and flashlight duration times.
After you have recorded a good natural color image, you are ready to record your Ultraviolet Induced Fluorescence image.
Don’t move the camera or change the focus.
Record your UV image in a similar fashion as the previous natural color image except this time use the UV flashlight to illuminate the object.
Check the histogram to make sure you have a good exposure. The UV exposure time will probably be different than your natural color exposure.
Once you have an image you are happy with, check the focus of both the natural color and UV images to make sure they are both sharp.
Repeat this process for all the objects you wish to photograph.
Note: Some UV lights also emit a fair amount of blue light and some sensors are sensitive to UV light so if you wish to only record pure induced fluorescence you will need to place a UV absorption filter in front of the camera’s lens to block the wavelengths coming from the UV light. I didn’t use any filters for these images.
That’s it! Hopefully this guide was helpful as you take your first steps into the world of ultraviolet-induced fluorescence photography!
About the author: Paul Illsley is a photographer based in Nova Scotia, Canada. With over 40 years of photographic experience, Paul’s work has been published by National Geographic, used by The Royal Canadian Mint in the form of a coin, by Canada Post in the form of a stamp and featured in a number of international publications. You can find more of his work on his website. This article was also published here.