Re: Lighting--Update to http://bicyclelighting.com
Steven M. Scharf wrote:
> "Victor Kan" <victor@usenet.NO_UCEloopdrive.net> wrote in message
> news:CKLhd.41698$hr3.1319916@twister.southeast.rr.com...
>
>
>>Is there a 3W halogen lamp with good focus characteristics that is
>>suitable for connection to a battery? If so, sounds like everyone will
>>be happy (at least us battery light users will get good light with much
>>longer run times than we're getting now with our inefficient 10W
>>systems, though neither of my 10W battery lights seems to do much
>>lighting up of trees--heck, I often wish they were less narrowly focused
>>so I'd get a little flood effect).
>
>
> Not sure which lamps you have, but the MR11 and MR16 lamps, which are
> commonly used in high end battery powered lights, are available in many
> different beam patterns. Often, on dual beam systems, you'll have one flood
> and one spot so you can select which lighting pattern is necessary in a
> specific situation. There is one available lamp head that is adjustable from
> narrow to flood, similar to Mag Lite flashlights. The MR16 is very
> efficient, the MR11 slightly less, due to the smaller reflector.
Perhaps it's time to discuss headlamp optics in more detail.
MR11 and MR16 lamp units are available in different "beam" widths, from
spot to flood, but the word "beam" is a bit misleading; the light comes
out in more of a fog than a beam. The faceted reflector is designed for
even illumination when pointed at an object to be displayed (such as a
statuary display, a painting, etc.). They want no sharp gradient in
light intensity, so the falloff of light intensity is very gradual at
the "beam" edges. For those who are mathematical, it's like a Poisson
(or "normal") distributon with a large standard deviation.
By contrast, items like flashlights have very "sharp" beams; almost all
light is concentrated in a very tight cone. The intensity gradient at
the beam edge is very sharp indeed. It's somewhat similar to having an
extremely small standard deviation - althought flashlights don't usually
give even illumination within their cone; they tend to hot spots and
cool spots.
BUT: Both flashlights and MR-series lamps are radially symmetric! That
means, if the dead center of the beam points squarely at a spot on a
wall, the brightness is the same all the way around a circle which is 5
degrees off center; or ten degrees off center. The light is "round."
(There's actually a very slight deviation due to the length of the
filament, but it's negligible.)
This is not optimum for headlights! There is NO other road vehicle
light that uses such a pattern! Instead, car lights, motorcycle lights,
moped lights, etc. ALL shape the beam so almost no light is wasted
upward; so the beam is directed into the travel lane, where it's needed;
and so the light gives an acceptable illumination gradient when it
shines onto a roadway that is nearly parallel with the beam direction.
Top quality bike headlamps are designed this way too. They shape the
beam into either a rectangle or a trapezoid, so the great majority of
the light goes to _exactly_ the right spot. As an example of their
sophistication: the better ones specify which edge must face up,
because even if it's a rectangular beam, they make the bottom part of
the rectangle a little dimmer, since it hits the road closer; they throw
more lumens into the top part, since it shines further down the road.
Comparing a 20-watt MR-16 bulb to this level of optical sophistication
is like comparing a scalpel to a heavy sharp rock. You can do
exploratory surgery (or see down the road) with either, I suppose, but
one is going to waste a lot more energy, and generally make a mess of
things.
In everything else regarding bicycling, the technology has developed
toward sophistication, toward lightness, toward efficiency and
precision. This is true of frame design, tires, spokes, and all other
components.
Only in the case of headlights do we have people seriously claiming that
"more is better, efficiency be damned" is the proper approach!
> If you look at the chart of efficiencies, the battery powered systems are
> far more efficient in terms of the amount of energy used per lumen,
> especially when you over-voltage. So don't fall for the lie about
> "inefficient battery powered lights, there is absolutely nothing to back up
> that claim.
Let's see: We'll suck energy out of the wall socket and store it in a
chemical tank; we'll remember to do this precisely correctly, or we'll
get stranded in the dark; and we'll waste most of the energy (or lumens)
by throwing them all over the forward half of creation. And we'll
replace our chemical tank every few years after it doesn't work any more.
I understand this works OK for lots of people; but it's just not my idea
of efficiency!
--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
edu]
