Re: OT for Ally - Just finished reading Episode 16

In message <qfwrkp10vm.fsf@xxxxxxxxxxxxxxxxxx>, Robin Fairbairns <rf10@xxxxxxxxxxxxxxxxxx> writes
"Mike Ruddock" <michael.ruddock@xxxxxxxxxxxxxxxxxx> writes:

"Robin Fairbairns" <rf10@xxxxxxxxxxxxxxxxxx> wrote...
i used to whinge about a helium-cadmium laser we had at work, which
produced an even shorter wavelength than them leds -- fiendishly
dangerous to the eye, if they ever got in there.

and then i left the firm, and thought no more of it.

then those bl**dy blue leds came along and although they're not actually
dangerous (afaik) they have the same doleful effect on my focusing.

i was actually impressed that they had managed to make leds with such a
short wavelength, until i saw them in real life.

The effect is probably due to chromatic aberration in the eye
lens. Like all simple lenses it is subject to both chromatic and
spherical aberrations.

not necessarily, however. the fact that i'm somewhat blue-yellow colour
blind could mean that i'm defective in blue cones (the other possibility
is that i have broken circuitry in the "blue-yellow comparator" which
sends a difference signal to the brain (there is no direct blue signal
to the brain, aiui).

if i'm short of blue cones (i.e., it's all down to the nerves), i can
produce a hand-waving argument that produces the effect i see, without
appealing to any of the known failings in the optical machinery of my
eye.

In my case I became aware of the latter when in
school and used to have to peer at the blackboard (we still had them
in my day, though some of them were yellow and used blue chalk)

(aaarrgh. i never saw any but white chalk in school. i wonder if
that's where the powerpoint loonies got the idea their original, broken,
default colour scheme...)

through a pinhole in a piece of card to allow me to focus on the
writing. (Later I wore spectacles!) I became aware of the former when
watching a theatrical performance where the stage lighting was changed
from red to blue and the objects on the stage were fuzzy with the
latter but sharp with the former.

The pinhole effect shows that I was "short" sighted (ie light from
distant sources comes to a focus closer to the lens than average). It
is possible that long-sighted folk may not have the same problems with
blue light that I do ...

fwiw, i'm somewhat long-sighted.

How do they get on with red light?

not as hard for me as blue.

and i also have problems with "white" leds, which (for me) produce
flashes of blue ... can't think why that is. (i don't even know how
white leds work; wikipedia isn't terribly enlightening there.)
Whereas I may be the only 'rat to have had my cataract surgery performed without the usual substitution of an intra-ocular lens* (used incidentally, not just to correct the eye's lack of lens but to filter UV light from the now otherwise unprotected eye. I noticed recently whilst standing sideways on to a large screen TFT type monitor that when the 'blank' screen defaulted (as it appears to) to blue, I experienced a glare effect in my vision. Others did not experience this so I think it might have been the screen was busy in the UV part of the spectrum. I was advise to wear sunglasses when outdoors but actually find that a deep peak cap does the job for me. I do resort to sunglasses (incorporating UV filter) in brighter weather.

*Because I was acutely myopic before cataract surgery, it was decided that once the lens was removed from the front of my eye, the optical result would be almost neutral so to speak. It was felt that the correction required was so little that any possible gain was less than the possible risk of infection from inserting an I-O lens.

Toodle Peep,

Mike
--
Mike McMillan,
The email address is spam trapped but any genuine communications may be sent to
mike dot mcmillan at ntlworld dot com

"Let's all calm down shall we? Let's forget there is a llama in here at all."
(Lynda Snell, 010603)

Tel: (+44) 0118 9265450. website: <http://homepage.ntlworld.com/mike.mcmillan/>
.

Relevant Pages

  • Re: OT for Ally - Just finished reading Episode 16
    ... produced an even shorter wavelength than them leds -- fiendishly ... then those bl**dy blue leds came along and although they're not actually ... The effect is probably due to chromatic aberration in the eye ... watching a theatrical performance where the stage lighting was changed ...
    (uk.media.radio.archers)
  • Math, SCIENCE and the PROVEN behavior of the NATURAL EYE. (Second-opinion SCIENCE).
    ... (The ability of the natural eye to change its refractive STATE -- ... based on the application of a plus and minus 3 diotper lens.) ... "Nearsightedness is not a very severe handicap, ... thrust upon you and you do not understand the reasons why you must use ...
    (sci.med.vision)
  • Re: Simple plus lenses do not work
    ... it does not stop enlargement of the myopic eye. ... in the retina," Dr. Phillips said. ... The researchers developed a dual-focus soft contact lens with a central zone ... the second period when the lenses were swapped. ...
    (sci.med.vision)
  • Support by THE PERSON HIMSELF -- AND PREVENTION-MINDED DOCTORS.
    ... this must ALWAYS DEVELOP BEFORE ANY MINUS LENS IS APPLIED. ... help nearsightedness, and quite probably make it worse. ... minus lenses at each subsequent eye examination. ...
    (sci.med.vision)
  • Re: Big Eye Ball
    ... evolutionists do not take the time to figure out what a species is, ... It's got a lens for starters. ... DNA to make it round and sit at the front of the eyeball. ... eye passed on their genes. ...
    (talk.origins)