On Fri, 23 Feb 2018 14:28:26 -0800 (PST), Andre Jute
wrote:

On Friday, February 23, 2018 at 7:32:33 PM UTC, Jeff Liebermann wrote:

Please note that I make no claims that a single number will provide
sufficient information for a comparison of lighting suitability,
superiority, performance, visibility, optimum pattern, etc.

It's anyway pretty rare outside the pure sciences that a single
measure of benefit or goodness (or badness) will tell you
everything you need know. Practical applications just don't
work like that.

That's easy to remedy. Permit me to introduce my "Index of
Conformity(tm)" which measures how well someone agrees with my
reference opinion, which I hereby declare to be optimum and a de facto
standard. 100 is total agreement and 0 is total disagreement. By
comparing your prejudices, biases, impressions, and premature
conclusions with my optimum reference standard, as single number can
be used to measure your conformity to my ideal. For example, if you
were to purchase or build a bicycle lighting system exactly like mine:
http://www.learnbydestroying.com/jeffl/pics/bicycles/slides/bicycle-flashlight.html
your system would be rated at 100. Any variations from this will
result in a lower score.

Even graphs with a single measure over time are only "singular"
for whatever appears on the other axis by the courtesy of assuming
time is a constant, even though we've accepted since 1905 that
time is a variable like any other.

I think it's safe to assume that bicycles will never achieve
relativistic speeds. Questions of time dilation, time travel, and
causality should not enter into the discussion.

Incidentally, "time is natures way of keeping everything from
happening at once". I forgot from whom I stole that. Unfortunately,
that didn't happen on Friday, when just about everything I attempted
failed badly and I was forced to work until midnight, subsisting on
half a sandwich, of questionable origin, that found in the fridge.

I'm used to working with huge, expensive statistical studies
at the interface of demographics and motivational psychology,
to be used in making decisions that will cost (or lose) millions,
sometimes billions -- I used to dramatize the risk of carelessness
for my people as the number of jobs lost. From a strictly
mathematical, theoretical statistical viewpoint, the number of
assumptions and guesstimates from experience one is required
to make even in a well-studied field can be disturbing, even
discouraging to the newbie until he discovers that applied
statistics is an art form for high rollers and the super-confident.

85.46% of all statistics are made up for the benefit of the current
audience. I'm fortunate in never having had to make a major financial
decision solely on the basis of statistics.

It's this background that leads me to welcome a meaningful,
simplifying, summing shortcut like your square-meter equivalent
circle. Together with the distance at which the light from
the lamp fills the circle and simple, well-known science,
in this case the inverse square root law,

That's called the "inverse square law". No "root" included. Lux
(brightness) is proportional to the square root of the change in
distance. Lumens (luminous flux) does not vary with distance.

it can let you estimate both the spread and the intensity
of a properly designed lamp at
distances useful to a bicyclist. Pity it won't tell you about
the hotspots as well, or nearfield spill from the thickness
of the lens, but then you can't have everything.

Opinions vary:
- Frank wants brightness limited to avoid blinding oncoming motorists.
- SMS wants some upwards spill to help see overhanging branches.
- You seem to want (not sure) more beamwidth to help see the roadside.
- NASA wants even lighting and no hot spot so that press release
photos look good.
- Barry wants only the forward facing area to be considered (beam
lumens), discarding the dim spillage as useless light.
- I want megalumens so I can set fire to the riders clothes ahead of
me. I also want megalumens because my principle use is "be seen"
lighting, which means I want to get the attention of motorists.

One number is definitely not going to be enough for a buy decision
from the above picky customers. The way I look at the problem is that
it's my light and I'll do with it what I find useful. If I want any
of the aforementioned illuminating aberrations, I'll do it somehow. If
conditions or ambient lighting changes, I want the ability to adjust
the intensity and beam pattern for those conditions. One number is
not going to work even for my buy (or make) decision.

So, why bother with lumens? Because in my never humble opinion, it's
a big part of the buy (or make) decision. I would guess(tm) it would
be #2, after beam pattern. It's not the sole criteria, it's not the
ultimate decision maker, and small differences are not going to
matter. Lumens are just one factor in the buy (or make) decision
which is currently horribly distorted by many vendors, and is not
easily verified by the buying public. What I'm trying to do is
provide the GUM (great unwashed masses) a means of verifying that the
stated lumens are something close to manufacturers claims. I believe
I've done that successfully.

Yo, Scharfie: I liked the integrating sphere until I discovered
you need a guy in a white coat to operate it. I'm allergic to men
in white coats: simply too much experience of ticket-punched
railroad minds telling me what I can't do, and expecting to be
paid after I did it myself. Men in white coats are never worth
the rise in blood pressure that accompanies their advent.

I have a white lab coat somewhere. I don't wear it any more because
I've grown in girth and it no longer fits. One of my competitors has
everyone wearing lab coats. To the customers, it creates the
impression that they know what they're doing.

I had one of my flashlights calibrated at the local university last
year. They wouldn't let me run the measurement, so I arranged (i.e.
bribed) a grad student to do the work. (He didn't wear a lab coat).
After about 45 mins of "calibration", he successfully produced a
number that was off by a factor of 10. We dug through the
measurements and calculations for about 10 mins and found the
arithmetic error. Incidentally, the professor in charge kept sticking
his head through the door and into the lab every 10 mins to check what
we were doing. He wore a white lab coat.

Andre Jute
Women in white coats are an altogether different matter

Nope. That usually represents a hospital or medical office
environment, which I do my best to avoid.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558