of questions keep coming up about the use of LUX in the
reviews of lights on this site. Numerous times I have stated
quite specifically that:
is the measurement of the maximum output from the brightest
part of the beam (the center). Lux is directly affected
by focusing optics and reflector design.
manufacturers state the output of their lights or bulbs
is the measurement of the overall output. Lumens is all
of the light measured no matter where it goes.
lights may produce the same number of Lumens, but different
Lux at beam center due to the focus of the reflector.
Lux is NOT a reliable measure of the overall light produced
by a light. It only tells you how well the light is focused.
asks, why don't you give both LUMENS (overall light produced)
and LUX (light focused to the beam center)? Well, it's not
that easy. Measuring LUX is easy, you just need a cheap Lux
meter, which I have. To accurately measure LUMENS, you need
an integrating sphere and all the associated equipment. If
someone would care to donate the $10,000 - $20,000 for the
sphere and the equipment, I would be happy to measure LUMENS
for everyone. No takers? Didn't think so... (UPDATE: See LUMENS
FROM LIGHTBOX READINGS???)
my budget is a touch smaller than the $ figures stated above,
I decided to put together this little apparatus to measure
RELATIVE TOTAL OUTPUT from a light (NOT LUMENS!!!). The light
measured would need to be reflected around and not from a
beam directly striking the meter sensor. It had to be something
similar to shining the light at the ceiling of a white room
and having the meter on the floor, thereby getting a sense
of the overall reflected light that hits the sensor. Since
I don't have a spare room painted white on all six sides,
I needed a box that was white on the inside. How about a milk
carton? White, cheap, easy to replace, and easy for almost
anyone to replicate!
the milk carton with aluminum foil to avoid light leakage
in or out. 2 holes were cut - one in the center of the side
for shining the flashlight through, one on the bottom for
the meter sensor. A 1" x 3" strip of paper was taped
to the inside of the hole on the side to act as a baffle so
that none of the beam from the flashlight would directly strike
the meter sensor.
I removed the "bottom" (side opposite the illumination
port) and the entire inside of the box was coated with 2
coats of Red Devil Acrylic Latex Enamel RDHP2402 Satin White
paint. Result: Almost identical readings. So it appears
that "whiteness" of the box is not really a factor...]
A light meter and a milk carton!
bunch of people have been asking what the baffle looks like
so they can make their own lightbox. Here it is. This piece
of paper hangs down about 1/2 inch inside the 180 deg. arc
of the top hole nearest the light sensor.
methodology was very simple - hold the light in the center
of the top hole, bezel even with the surface of the carton,
shine the light straight down and take a reading. Is this
super scientific? Absolutely not! Is is comparing the relative
amount of overall reflected light from the flashlights? Pretty
we may not have an integration sphere, but at least this should
give a general idea as to which lights' output are brighter
overall than others. The brighter the light, the more reflected
light that will hit the meter sensor. Also, lights with the
same battery/bulb configuration should read the same regardless
of how tight the beam can be focused with the reflector or
this apparatus, for example, a single white LED 6V light that
is focused to a tight beam should read just about the same
as a single white LED 6V light that has no optics and just
produces a flood of light.
REMEMBER - there is a lot of room for error here, so I wouldn't
say specifically that a light with a reading of 500 is necessarily
putting out less light than a light with a reading of 510.
Suffice to sat that these 2 lights would be just about the
same. However if you see a reading of 500 vs 2000, it should
be safe to say that the 2000 light is about 4 times brighter
than the 500 light. I'd say at a guess that if the numbers
are within about 15% of each other, they're putting out about
the same amount of light overall.
I have had one person who uses a similar but different method
of overall light measurement report that the numbers they
have obtained correlate with mine! That means that the data
from this project is somewhat valid!
The data has been combined in a chart with the LUX readings
of many of the lights so you can see "throw" and
"overall output" in one chart.
the way, we had an official naming contest for the units produced
by this device on CandlePowerForums some time ago and the
winner was QUPS (Quickbeam's Unofficial Photonic Standard)
- Just in case you see the overall output numbers mentioned
as QUPS on CPF (my username on CandlePowerForums is Quickbeam...)