On Fri, 23 Feb 2018 08:28:10 -0800, sms
wrote:
On 2/21/2018 12:21 AM, Jeff Liebermann wrote:
Also from several revious rants, if you draw a 1.13meter (44.5inch)
diameter circle on the wall, and shine your bicycle head light or
flashlight on the wall until it fills the circle, the lux meter will
read directly in lumens. It works because the area of the circle is 1
square-meter and:
1 lux = 1 lumen/sq-meter
If you light produces a non-circular spot on the wall or an uneven
pattern, just guess(tm) until you have a spot that looks roughly like
1 square-meter. No warranty for accuracy expressed or implied.
You need to build an integrating sphere.
http://forums.mtbr.com/lights-diy-do-yourself/diy-integrated-sphere-780122.html
Or buy one. http://www.pro-lite.co.uk/File/general_purpose_spheres.php
Did you happen to notice that they cost thousands and require an
expert to operate?
https://www.youtube.com/watch?v=mvyptpA-BmY (Light and Motion)
https://www.youtube.com/watch?v=11XrP51WzfE (Lezyne)
I built one from a paper mache newspaper ball. Something like this:
http://budgetlightforum.com/node/31356
It fell apart.
I also built an "integrating pipe" out of PVC plumbing parts.
https://www.youtube.com/watch?v=k2Dbmz8WXmE
Calibration and repeatability are problems.
The nice thing about an integrating sphere is that it works for most
any light source including light bulbs. Mine only works for
flashlights and headlights. Because of the lack of a well defined
pattern, my method won't work with bicycle tail lights.
What I'm trying to is give the average bicycle headlight buyer a way
to get a ballpark number for lumens produced. As long as the pattern
displayed on a wall is roughly circular, my method will produce a
tolerable approximation. The accuracy is lousy and considerable
guesswork is required, but in general, the results are amazingly close
to the manufacturers specs (when the manufacturer isn't fabricating
numbers).
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.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558