I am especially interested in human visual sensitivity to UV light. Most people do not see UV light because the lens absorbs UV. After cataract surgery, a condition called aphakia, "near" UV light (300 - 400 nm) can reach visual receptors. My interest stems in part from my own condition of being aphakic in one eye. There was surprisingly little information about human UV sensitivity though the topic was becoming increasingly relevant in view of the mounting evidence for UV damage to the vertebrate retina. Using traditional psychophysical methods, I determined the photopic (cone) spectral sensitivity into the UV portion of the spectrum and determined the UV absorption by the macular pigments, carotenoid screening pigments in front of the fovea. I compared the scotopic (rod) spectra of aphakic observers and normal subjects and deduced the UV absorbance of the lens. I used chromatic adaptation to show that individual cone types were more sensitive to UV light than expected on the basis of their resident rhodopsins. What does UV light look like? Actually, it looks a desaturated (whiteish) blue. My demonstration of this is a Blak-Ray (UVL-56) lamp where I have replaced the filter with Corning filters #5840 (7-60) [UV] and #5330 (I-64) [blue] -- these both look the same to my aphakic eye. I speculate that UV looks whitish blue because all three cones are sensitive to UV light but that the blue cone is especially UV sensitive.

On the side, I was interested in how to take photographs in the UV. Already, there had been numerous published photographs to dramatize how different flowers would look in the UV to their insect pollinators. When my son was in junior high school, and I was the dad, I helped Dan with a science project to determine feasibility. With a Corning filter for near-UV (300-400 nm) in front of the camera, we found that the ASA (ISO) of Kodak 2415 Technical Pan film (developed in Kodak HC110 at dilution D) is very fast (about 6400). That means that if you have enough UV light, your camera light meter will probably work and not be very far off if you set it at the film's nominal ASA (400). Here is a photograph I took of the flower of Zygadenus nuttalii (UV light on the left and white light on the right) in a collaboration (P. Bernhardt, Chap. 9 Anther adaptation in animal pollination, in W. G. D'Arcy & R. C. Keating, The Anther, Form Function and Physiology, Cambridge University Press, New York, 1996). For these photographs, I used a Nikon F camera and a Nikkor 55 mm lens. For UV illumination, I used GE F15T8 BLB "black" lights, high in the 300-400 nm range, and a time exposure of about 30 s was necessary. These days, virtually nobody uses film. Here (right) is columbine in UV light. A white light photo is in the middle, and a digital camera snap shot from my garden is on the left. Note that the yellow, as well as the red are fairly dark to UV. Here is my rhododendron, again with yellow being UV-dark. And here is catalpa. Methods -- A MTI CCD 72 camera and a Fujinon TV 1:1.7/35 lens (and a flower) are under a bank of UV lamps (right); computer and monitors are on the left; see this paper for image capture details.

Memoirs

Because of a traumatic cataract I had when I was 10, and surgerry when I was 12, I could see UV light, and that proved very convenient with my interests in Drosophila UV vision. In the 1970's, I noted that there was very little literature on human UV vision. I met Charles White who showed me a very thorough study, a dissertation by Karel E.W.P. Tan from Utrecht. I wondered why it had not been published, so I called Mat Alpern (Tan's mentor) and Dan Green at the University of Michigan. They said the work was wholesome but that Tan had lost his "publish or perish" motivations because he was a clinician. I contacted Tan and we agreed to publish a comparative review of UV vision. It was later, 1982, that I met Karel in Utrecht. At the time it was published, there was little work on vertebrate UV vision, but soon after that, the dam broke and there was a flood of work on fish, birds and other vertebrates. Soon after I brought De-Mao Chen from Shanghai for a brief post-doc, he worked on birds with Tim Goldsmith at Yale. Chen later returned to my lab and worked with me for 8 years. I went up to Montreal twice to work with Charles White in preparation for the human psychophysics work I published in the late 1980s and early 1990s.


My papers on human UV vision:


Stark, W.S. and Tan, K.E.W.P. Ultraviolet light: Photosensitivity andother effects of the visual system. Photochemistry and Photobiology, 1982,36, 371-380. (Invited review to accompany American Society for Photobiology1981 Meeting Lecture). PubMed

Stark, W.S. Photopic sensitivities to ultraviolet and visible wavelengths and the effects of the macular pigments in human aphakic observers. Current Eye Research, 1987, 6, 631-638. PubMed

Griswold, M. S., Stark, W. S. Scotopic spectral sensitivity of phakic andaphakic observers extending into the near ultraviolet. Vision Research,1992, 32, 1739-1743. PubMed

Stark. W. S., Wagner, R. H., Gillespie, C. M., Ultraviolet sensitivity of three cone types in the aphakic observer determined by chromatic adaptation.Vision Research, 1994, 34, 1457-1459. PubMed

A science feature that relates to my interests:

David Hambling, Let the light shine in (you don't have to come from another planet to see ultraviolet light), The Guardian, Thursday, May 30, 2002, on line

The yellow lens blocks UV vision in people. These fresh lenses from the eye bank are from 79 year old (top) and 39 year old (bottom) donors.

The lens absorbance inferred by subtracting the scotopic (rod) spectral sensitivities of normal from aphakic (lensless) observers (from Griswold and Stark, 1992)


Here is a handsome 38 year old subject participating in the psychophysical study published in 1987

Here are human aphakic cone photopic sensitivities on fovea vs off fovea. The difference centered around 460 nm is due to the macular pigments.

Here are scotopic sensitivities from aphakic and normal observers. The difference in the UV is due to the lens.

Short, middle and long wavelength cone spectra were determined by spectral sensitivities against chromatic background. Short and long wavelength cone spectra are much higher in the UV than expected from a rhodopsin with a cis peak.

Why UV looks a desaturated blue. Tan's data (left) and the color diagram (right). Violet to red traced clockwise around the horseshoe, white inside. Wavelengths below 400 nm trace toward the white and blue. This relates to the previous figure showing that all three cones are UV sensitive, especially the blue cone.

Here are Monet's water lillies at Giverney painted before (left) and after (right) his cataract surgery

This page was last updated on July 28, 2005

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