Ultraviolet light (UV) is invisible to the human eye but when certain substances are exposed to it, they emit visible light which we can see. This phenomenon is called fluorescence. I became interested in photographing fluorescence when a friend told me that scorpions appear bright blue under UV. People rarely see scorpions because they are brown and well camouflaged but they are quite common where I live on the outskirts of Sydney and are easy to find at night by searching the leaf litter with a UV lamp.
My initial photos were disappointing because the backgrounds looked artificially coloured. I discovered that most ultraviolet sources, in addition to producing UV also emit coloured visible light and cameras often render reflected UV as unwanted colour. I made the equipment described below to prevent false colours appearing and a selection of images showing fluorescence are shown below.
The essential components of my UV lamp, were purchased in 2018 from ebay for around AU$50 and include:
- 10 watt 365nm UV LED. High output power of the LED reduces photographic exposure times and LEDs having wavelengths up to approximately 400 nanometres also work well.
- Filter to block visible light emitted from the LED. This filter appears black but is transparent to UV. I used a "ZWB2" filter. This filter and a good UV led are the most important components needed to obtain good photos.
- Resistor and heatsink to limit the maximum current and stop the LED from overheating
- 3.6 volt rechargeable lithium cell, charger and switch
- Condenser lens on the front of the lamp concentrates the UV into a brighter more intense beam which makes the fluorescence look more vibrant and reduces exposure times
- To prevent unwanted ultraviolet light from reaching the camera sensor you can use a UV blocking filter on the camera lens. Many cameras record UV as colour and UV filters sold as "lens protectors" often do not block the longest ultraviolet wavelengths. A "UV(0)" or "L39" filter stops nearly all reflected UV appearing as false colour in the image
Lens filter - Aluminium foil, UV exposure for 20 seconds, f16, Nikon D750 with and without a suitable filter
Marbled scorpion - UV exposure for 6 seconds at f16 and fill flash. Nikon D750, 180mm lens with extension tube and tripod
Fledgling Powerful owl feather (left) and Sulphur-crested Cockatoo feather (right)
Diamonds and Rubies
Australian $5 note
Lichen growing on sandstone