Re: More on lights.

On Fri, 26 Dec 2008 18:04:58 +0000, Ryan Cousineau wrote:

In article <oY75l.41156$T07.3099@xxxxxxxxxxxxx>,
Keiron <pop07kfk@xxxxxxxxxx> wrote:

On Fri, 26 Dec 2008 16:06:52 +0000, Peter Cole wrote:

terryc wrote:
On Fri, 26 Dec 2008 09:01:17 +0000, Keiron wrote:

I read the recent "bright lights" posting which got me in to a bit
of research which in turn revealed that red lights are better for
vision at night as they highlight obstacles with much less depth
perception issues and, whilst highly visible to those around are
much less blinding.

This is one of those areas of research that are interesting, but for
bicycle riders in the realm of sillness.

Think about it?
White light includes red light. Why throw away 7/8ths of the light?

The human eye has rod & cone cells. The rod cells are much more
numerous and 100x more sensitive to light, but they do not
distinguish color. The rod cell response peaks in the blue-green
wavelengths, and is virtually non-existent in reds. Rods give us our
night vision, but cone cells give us color and detail perception.

Some DIY bike light makers have deliberately used blue-green LED's
claiming a many-fold increase in actual perceived brightness. Sounds
good in theory. Red light can be used to preserve night vision
because night vision is insensitive to it.

Ah ok, this is perhaps the point the original source was trying to make
but better expressed here (or better understood I guess).

Red bike lights for illumination of
the road would seem to be a poor idea. Off-road, they'd make foliage
look very dark, another disadvantage.


What do you mean by detail perception in the first paragraph? For
example are there conditions were 3d detail would be increased and 2d
decreased or are such factors linked proportionally? I.e. in context:
would red light at night provide better outline information to the eye
i.e. picking out depth? or are surface and depth details the same?

You don't have to "throw away" light with modern LED lamps. LEDs are
quantum devices which naturally emit at a narrow wavelength. White
LEds are typically made by either blending light from multiple
monochrome LEDs or by exiting a blend of phosphors with a monochrome
LED.

What wavelength is this narrow band at or is it atypical?

LEDs are available in a variety of wavelengths. It's built into the
design of the LED. White LEDs have had bad habits in the past like
emitting only a few narrow wavelengths of light, but people are paying
more attention to this now (it's quantified now as the "Color Rendering
Index").

You might enjoy this 1995 article about the quest to build the first
blue-emitting LED, which has been key to the creation of white-emitting
LEDs as well:

<http://www.wired.com/wired/archive/3.03/blue.laser.html>

It explains a lot about how LEDs are made.

There's a short follow-up from 1998:

<http://www.wired.com/wired/archive/6.08/updata.html>

Cheers Ryan: most 'illuminating' read.



A monochrome blue-green LED certainly seems more efficient overall
when factoring the spectral sensitivity of the eye.

Fascinating! Thanks Pete, I understand green leds are available
commercially so I'll give them a shot until I have the savvy to build a
set.

There's some interesting study to be done here, but I think that
throwing away accurately rendered color by using oddball colored
lighting is not going to be fruitful for driving/riding lights. The
basic problem is that under odd-colored lights, some things are going to
be misperceived. Red LEDs are used in certain circumstances because they
don't wash out your night vision, but that's meant for cases where
you're going to briefly use the red LED, and then go back to looking
into a dark place. The goal with most "seeing" bicycle lights is to
eliminate the dark.


What you may find is that, for example, green LEDs are more efficient
than white LEDs in terms of lumens/W, which means you can throw more
green light out into the world for the same amount of power, or your
batteries last longer. If you can do that with minimal loss of visual
information, that might be a win.

Green, green/blue definitely seems worth exploring, cheers.
.

Relevant Pages

  • Re: More on lights.
    ... research which in turn revealed that red lights are better for vision at night as they highlight obstacles with much less depth perception issues and, whilst highly visible to those around are much less blinding. ... Rods give us our night vision, but cone cells give us color and detail perception. ... Red light can be used to preserve night vision because night vision is insensitive to it. ... White LEds are typically made by either blending light from multiple monochrome LEDs or by exiting a blend of phosphors with a monochrome LED. ...
    (rec.bicycles.tech)
  • Re: More on lights.
    ... non-existent in reds. ... Rods give us our night vision, ... LEDs or by exiting a blend of phosphors with a monochrome LED. ... LEDs are available in a variety of wavelengths. ...
    (rec.bicycles.tech)
  • Re: More on lights.
    ... White light includes red light. ... Rods give us our night vision, ... us color and detail perception. ... LEDs or by exiting a blend of phosphors with a monochrome LED. ...
    (rec.bicycles.tech)
  • Re: More on lights.
    ... White light includes red light. ... Rods give us our night vision, ... us color and detail perception. ... One practical matter though is that there's a lot more interest in high power white LEDs than blue-green ones, so white LEDs in high wattage have become more available since the time of this article. ...
    (rec.bicycles.tech)
  • Re: Stocked up with 100w bulbs yet?!
    ... the persistence of vision makes the light look brighter ... It is a way of saving on electrical power. ... LEDs can be powered such that they emit continuous light (like if you power ...
    (uk.legal)
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