I have something to add to Alan Larman’s experience of seeing ultraviolet (15 March, p 33). I underwent a cataract operation involving eye lens replacements. Some time later I visited a research lab at the University of Cambridge. The team had just taken delivery of a UV laser emitting a beam with a wavelength of 355 nanometres, and was having trouble aligning it in their optical set-up. I found I could see the beam clearly, and aligned it for them without difficulty.
When they asked me what colour I saw, I had to tell them that it was, disappointingly, no different from the violet light from their existing 405-nanometre laser, which they could all see. I wonder whether anyone has researched this interesting phenomenon.
Wolverhampton, UK
