On Tuesday, December 5, 2017 at 1:40:39 AM UTC-5, Jeff Liebermann wrote:
On Mon, 4 Dec 2017 20:19:24 -0800 (PST), Sir Ridesalot
wrote:

What I like to see on a website is an image of the ACTUAL BEAM PATTERN on the road not a wall.
Cheers

It's difficult to see variations in brightness on the roadway, where
everything on the road, trees, sidewalk, cars, dirt, concrete,
asphalt, street signs, and such, reflect light by varying amounts. For
example, if the road was made from a glass mirror, you would see
nothing because all the light would be reflected in the forward
direction and none would be reflected back towards the rider. Vertical
objects, like people and trees, appear brighter because more light is
reflected. So, if you want a "realistic" test, you end up measuring
reflectivity, not illumination.

Peter White's photos seem to be close to the way you are asking. The
problem is that it is difficult to see the variations in intensity. If
I accentuate the difference in light intensity using pseudo color
proportional to the (reflected) light intensity, I get a more
interesting picture. You can more easily see the hot spot(s),
pattern, beam width, and side lighting, like this:
http://802.11junk.com/jeffl/pics/bicycles/Front-Light-False-Color/index.html
Each (pseudo) color has a corresponding lux (brightness) value (which
I didn't bother trying to calculate). All the photos on the page are
of the same headlight and were derived from the color photo on Peter
White's web site. (Ignore pseudo-color-01.jpg, which is a duplicate
of one of the others).

Unfortunately, I've done nothing with this beyond the initial
tinkering. If any one is interested in how this was done, I'll dig
out the info and post it.

There certainly is difficulty with beam shots. It's tough to accurately
represent what a person sees with their naked eye. And I suppose it's
possible that people's night vision varies, so a beam shot that looks "right"
to one person may look wrong to another. I imagine most people posting those
images are trying their best, but I'll bet that their camera settings are
mostly by guess and by golly.

Even the split-screen comparison web pages suffer from this difficulty.
They can show if one light is brighter than another, but it's hard to tell
how bright is bright enough. I think they tend to push a "brighter is
always better" attitude.

I've decided that Peter White's photos do the job for me. I've bought
several headlamps from him, and ISTM that the lights performed as I expected
they would.

And I appreciate your effort with the false color conversions, but personally,
I find them hard to interpret. They can tell me how even the beam is, but I'd
still have to guess at whether it's even or bright enough for me - or too
too bright.

- Frank Krygowski