[SML] Blue lighting, somewhat OT

[James Alderson]

Brent Logsdon wrote:

"I am seeing refraction/offset with blue LED. ?I am fairly certain this is
a function of my eyeglasses but I am so nearsighted that I cannot verify by
trying this without glasses. <snip>
White LED fixtures using blue LED and a phosphor plate can appear as a
white-lit fixture with a blue dot floating to the side of the fixture. An
arena audience lit with an LED wash can appear to jump over by a seat or
more if the source switches to blue LED only.?
Anyone else having a similar response??
Polycarbonate lenses, no glare reduction coating, no lens tint, very
nearsighted and astigmatic."

I'd agree it is your glasses. I used to get a similar effect. I too was
very myopic (clear vision at about 5 inches), high index rather than
polycarbonate lenses, and I also got the blue offset. I used to see it when
looking at deep blue incandescent strip lights or spotlights with an R80
filter. The filters were deep blue but a lot of red also leaks from the
other end of the spectrum (check out the spectrum on R80. It peaks on both
ends). So I'd see a double image, one red and one blue.

Lenses are prisms, so will bend different wavelengths by different amounts.
When you have as narrow and isolated frequency band as a blue LEDs put out
you'll get that distinct separate image. It's similar to the chromatic
aberration that creates a blue ring on the edges of spotlight beams. The
different wavelengths of the spectrum get broken up but tend to blend back
together into an even field of white light over most of the beam, except at
the extreme edges where the blue stays separate. It's physics.

Since I got cataract surgery last year my prescription went from -10.5 to
-2. For me the chromatic separation has more or less disappeared. There
isn't enough separation to be noticeable with the weaker lenses. It
wouldn't hurt to ask your eye doctor at your next regular checkup, but I
wouldn't be too concerned.

Mick Alderson
TD, Fredric March Theater
UW Oshkosh
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