Ultraviolet Fluorescence

Diamonds

 

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

 

UV lamp

 

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

 

Eggs

 

Lichen growing on sandstone