This proposed new standard for flashlight testing isn't my idea; but I *was* given permission to pass it along. I hope this isn't the wrong forum, as I'd hate to find out it needed moving.
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Methods for measuring light output from a flashlight (or headlamp)
September 2003
Henry Schneiker
HDS Systems, Inc.
Henry@hdssystems.com
Copyright 2003 by Henry Schneiker, HDS Systems, Inc., Tucson, Arizona,
USA
All rights reserved.
This is a proposal for a new standard for the flashlight industry. It
is intended to provide useful information to a potential customer that
can be use to compare flashlights and to eliminate the non-productive
claims common in advertising. It is envisioned that this standard will
be owned by a flashlight trade association. The idea for this standard
and a flashlight trade association was put forward by Brad Penny of
Streamlight at the February 2003 Shot Show in Florida.
Units of measure:
The metric system will be used. Distances will be in meters.
Illumination will be in lux. Time will be in hours. Angles will be in
degrees. Temperatures are in degrees C.
Samples used for measuring light output:
Light output will be measured from fully assembled standard
configuration units. The units must accurately represent what will be
purchased by a customer.
A minimum of 5 sample units shall be tested. If possible, sample units
from multiple production batches should be tested.
Batteries used for the test shall be typical of what a customer can
easily acquire or what is shipped with the product, whichever results
in the lower output. If there is a significant difference between
these two figures, it is acceptable to prominently specify on the
packaging and in the manual that specific batteries are required to
obtain the rated performance and that use of other batteries will
reduce performance.
Temperature:
Tests shall be performed at 25 degrees C.
If the light is designed to be hand held or otherwise mounted to
improve the heat flow during operation, it is acceptable to provide a
comparable thermal path during testing.
Result values:
The results shall be an average of all tested sample units. If the
ratio between the best and worst sample unit is greater 1:0.91, the
results shall also include a standard deviation. However, if the
sample size is greater that 10 and a single sample deviates
significantly from the data cluster, that single sample may be
discarded if it can be reasonably demonstrated that the sample was
defective.
It is acceptable to understate results only if the understatement is
uniformly applied to all corresponding results. However, the stated
final result may never by less than 0.75n, where n is the result.
Measuring solid angles:
Many measurements in this standard require an origin for measuring
solid angles. The origin for angular measurement is the center of the
light emitting surface. The axis of the solid angle aligns to the beam
axis.
Measuring distances:
Distances are measured from the exterior surface of the sample unit
lens, the exterior surface of the light meter lens or other specified
surface. If the measurement is at an angle, the point on the lens
where the angle intersects the lens may be used instead of using the
center of the lens.
Brightness:
Brightness is defined as the average surface illumination of a surface
perpendicular to the beam axis intersected by a 10 degree solid angle
in lux at 1 meter.
If a distance other than 1 meter is chosen, the data shall be
normalized to 1 meter using the inverse square law. The distance
chosen must allow the light meter to provide 3 significant digits of
data - ignoring the decimal place.
The brightness measurement shall be taken between 0.3rt and 1.0rt,
where rt is the rated runtime of the light.
Reach:
Reach is defined as the distance in meters at which all parts of a
surface perpendicular to the beam axis intersected by a 10 degree solid
angle can be illuminated to at least 10 lux.
Runtime:
Runtime is defined as the length of time the light can generate at
least 0.5b on a constant setting, where b is the rated brightness.
Beam angle:
Beam angle is defined as the solid angle within which the light
intensity is at least 50% of the rated brightness.
Beam pattern:
Beam pattern is a graph of angle versus distance where a point will
receive 10 lux of illumination.
The graph shall be constructed with angle lines every 10 degrees
starting with the beam axis. The beam axis shall be 0 degrees. Angle
lines shall meet at either the bottom or left side of the graph and be
centered on that axis.
A set of shadow lines shall denote the angle at which 100% of the light
emitter is occluded by the housing. The area beyond the shadow lines
may be left blank.
Beam pattern symmetry:
The beam pattern is normally symmetrical about the beam axis. However,
if the beam pattern is not symmetrical, measurements should be made
with the beam in the normal orientation of use. Definitions can be
expanded to allow elliptic surface areas instead of circular surface
areas when appropriate as long as the results state the axis dimensions
and orientations. An additional graph shall be provided for each
additional axis.
Packaging and literature:
The following items shall be provided as a group on packaging and in
literature:
* Brightness (e.g., Brightness: 300 lux at 1 meter)
* Distance (e.g., Distance: 5.4 meters (17.7 feet) at 10 lux)
* Run time (e.g., Run time: 2.3 hours)
* Beam angle (e.g., Beam angle: 16 degrees at 50%)
* Beam pattern graph (e.g., graph labeled: Distance at 10 lux)
Note that values should be truncated instead of rounded. This prevents
values from being accidentally overstated. Add another significant
digit if you need to.
Note that unit of measure and condition are considered part of the
value and should be always be specified. It is permissible to add a 1
lux distance following the 10 lux distance (e.g., Distance: 5.4 meters
(17.7 feet) at 10 lux, 17 meters (55.7 feet) at 1 lux). However, no
other variations are permitted.
Background information:
10 lux provides good color recognition and good visual acuity. The
eyes can quickly and easily adapt to this level of light when moving
from a bright office environment (100 to 200 lux) to a dark environment.
At 1 lux, you can easily see and identify shapes at 3 times the
distance provided by 10 lux, however color recognition deteriorates to
identifying only limited colors. Visual acuity is deteriorating
rapidly. Adapting to this level of light takes much longer than
adapting to 10 lux.
Below this level of illumination all remaining color vision quickly
disappears and visual acuity continues to deteriorate.
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I welcome any comments; they'll be passed on to Henry as appropriate - as he asked.
Proposed new standard for measuring flashlights
Linear Mode
