Fluorescence Illumination

By Mary Mihajlov

Introduction

Fluorescence is simply the process by which shortwave light energy is absorbed and reemitted as long wave light energy. It is most often observed under a UV or black light.  If you’ve ever been to a club that used black lights for lighting, you may have noticed that any white clothing you were wearing was glowing or that your dance partner’s teeth were glowing. That “glowing” was the process of fluorescence.

Items you encounter everyday fluoresce under a black light. For example: white paper. Paper is treated with fluorescent compounds to make it appear brighter and whiter.
 Club soda, laundry detergent, chlorophyll (specifically chlorophyll extract), antifreeze, postage stamps, some minerals and gems, vitamins, and currency are just a few examples. Several animals have been found to be able to fluoresce, specifically jellyfish and scorpions. Jellyfish fluoresce as the result of the synthesis of a protein known as the Green Fluorescent Protein. Scorpions contain a protein in the outermost layer of their exoskeletons that causes them to fluoresce. The purpose of their fluorescence however, is unknown

Below: Scorpion and detail shot

 

Applications

Fluorescence illumination is applied in a currently being applied in many ways. US currency contains threads in the larger denominations that fluoresce under black lights to protect against counterfeiting. New York state drivers’ licenses have a seal imprinted on each ID that is only visible under a black light. Postage stamps are also printed with inks that fluoresce. Fluorescence also has several applications in the fields of biochemistry and medicine. In the auto sequencing of DNA (specifically the chain termination method), molecules can be tagged with a “fluorescent label” making it easy to identify the terminating molecule. Fluorescence has also been used in the study of the structure and formations of DNA. Perhaps the best know use of fluorescent illumination is of that in the forensic science field. Television shows such as CSI often depict an investigator combing over a crime scene with a black light. Fluorescent illumination is often used in this field to detect fibers, hairs, fingerprints, and body fluids. Fluorescent illumination can also be used to identify different gems and minerals.

Below: $20 bill and New York state driver's license detail

 

How to Photograph Specimens Using Fluorescent Illumination

Equipment Needed:
-Black lights
-Digital SLR (or 35mm film SLR)
-Macro lens (I used a 60mm and 105mm)
-White light source
-Dark background (velvet, black paper, black felt – dark background is essential as a white or lighter colored background will glow under the black lights)

  • A general set-up of the equipment might be: a camera on a copy stand with two black lights positioned across from each so their illumination beams overlap. In this area of overlapping a specimen would be placed. Adding one or two more black lights for greater illumination is encouraged. Often, the amount of illumination needed depends on the specimen.
  • The photographer may want to photograph the specimen under white light first for comparison purposes later. White light is also useful for the purpose of focusing and camera placement.
  • Set ISO on camera to at least 1000. Photographers may find that other settings work better but ISO1000 is a good starting point.
  • Allow UV lights time to warm up to full power.
  • Turn out as many lights in the room as possible. This will minimize the chance that other light will interfere with your exposure.
  • Do several test exposures to test for the correct exposure. You might try exposure lengths of 2, 4, 6, or 8 seconds long at f/16 to still retain maximum depth of field.
  • Once you have found your exposure (and it may vary depending on the specimen), go nuts! If using a digital SLR, be sure to shoot in RAW as this format will allow you make color temperature corrections to the image.
  • As for postproduction work, Photoshop is recommended. UV/black light is very difficult, if not impossible, to color correct. Experiment by adjusting the levels and color balance. Fluorescent illumination will often photograph blue, so when color balancing experiment with different amounts of blue removed to see how close to the original colors fluoresced you can get.

Below: Two Examples of fluorescent minerals

 

 

Content and Photography by Mary Mihajlov

Contact author.

Links:

http://en.wikipedia.org/wiki/Fluorescence

http://www.pti-nj.com/fluorescence.html

 


Return to index of articles by students on the 'Principles and techniques of photomacrography' course, November 2006,
Biomedical Photographic Communications (BPC)
program at the Rochester Institute of Technology (RIT).


Article hosted on Micscape Magazine (Microscopy-UK).

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