Jeff Liebermann wrote:
On Wed, 21 Feb 2018 01:30:26 -0800 (PST), Andre Jute
wrote:

On Wednesday, February 21, 2018 at 8:21:42 AM UTC, Jeff Liebermann wrote:
On Tue, 20 Feb 2018 20:31:59 -0800 (PST), Andre Jute
wrote:

Sigh. I see that you haven't been reading my rants. That's the exact
model that I've recommended in at least three of my previous rants on
the topic. Also available on eBay and Amazon.
https://www.ebay.com/itm/222318701790
or search for "lux meter".

The more sources the better, then.

I have 2 other Lux meters. Both have removable sensor "pucks" which
allegedly make measurements easier. I've compared readings between
the three meters and find that they are all fairly close to each
other. I don't have a calibrated source, so I can't determine their
accuracy. The UNI-T UT383 above is the most useful because it's the
only one that has a peak reading feature. I mark the diameter of my
one square meter circle on the wall, turn on the test flashlight or
headlight, and walk towards the wall until the spot has the same
diameter. I then turn off the light, and the highest reading remains
on the display. Very handy for doing measurements without an
assistant.

If you want better accuracy, measure the hot spot in the center and
the brightness at the edges. I usually give it 33% above the edge
value, although 50% is probably close enough.

I like your DIY calibration test, though.

You might want to measure your various lights and headlights and see
how they compare with the published specs. If enough people do that,
maybe we can see an end to inflated lumens specs. I measured about 15
assorted lights and flashlights, but nobody seemed interested.


Both lux and Lumens stated are a guide really, or to put it another way,
I’ve noticed more difference from the beam shape than the claimed
Lux/lumens which makes sense since Lux is for bikes at least measured at
the 10 meter mark, and Lumens is generally what ever the led will can
produce.

What neither will tell you is how they light the trail/road, or to put it
another way seeing the light working is a far better test than lumen/Lux
stats.

And to be honest it’s best to see it as you where rather than seeing screen
shots as beam shots are difficult if not impossible to do fairly since
human eye and cameras do differ in this regard so some lights look much
better or worse in beamshots.

Roger Merriman