# Proposed new standard for measuring flashlights



## The_LED_Museum (Sep 25, 2003)

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.
[email protected]

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.


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## PhotonBoy (Sep 25, 2003)

Excellent proposal!!

How about some indication of a light's 'water-proofness' such as used in the watch industry?

Perhaps a second standard should be proposed for lights intended for wide area coverage, like lanterns.


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## Walterk (Jun 8, 2010)

So throw is the distance at which 50% of the area of the projected spot measures an intensity of 10 lux ...?


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## mudman cj (Jun 8, 2010)

This proposal suffers from the same issue as the relatively recent standard released by NEMA. If the 'reach' or 'throw' is based upon a constant lux value regardless of target distance, then the amount of light getting back to the user of the illumination device is not consistent between lights with different values for 'reach' or 'throw' because light returning from the target always drops off in intensity according to the inverse square law. See this thread for more detail.


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## Walterk (Jun 9, 2010)

So it would not be a practical value compared to real life situations.
But it would give a fair and objective means of comparing throwing-lights wouldn't it?


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## mudman cj (Jun 9, 2010)

It is not a fair means of comparing throwing lights because as the distance to the target increases, the actual amount of usable light returning to the user diminishes as the square of the distance. The results will tend to be fairly accurate for lights that we in the forum would call 'medium' reaching or throwing lights, but for very 'throwy' lights this standard (and the new NEMA standard) will become increasingly inaccurate at differentiating the throw abilites between lights of varying performance. 

Specifically, the problem will come where someone has a far-reaching light with 'x' throw and they want a light with '2x' throw. If they use a standard like these they will be disappointed because the actual increase in throw will be far less than 2x. Furthermore, if someone tries to compare lights A and B with different throw or reach capabilities, they will again arrive at incorrect conclusions regarding the relative throw ability of the lights compared to one another using a standard that does not account for the laws of physics. 

Using this proposed standard or the NEMA standard, one would conclude that 4 times as much lux would be required to throw twice as far. And while that does illuminate a target with the same lux, if the target is twice as far away then only half the lux reaches the eyes of the user as compared to the closer target. Additionally, as the difference in throw between the lights increases, so does the magnitude of the error.

*In summary* - While this proposed standard and the NEMA standard can tell us which light has more reach or throw, they cannot accurately tell us how much more reach or throw one light has than other, especially as we compare lights with greater and greater reach or throw ability. Nor can they tell us how much lux we would need to be able to use the light to see a given distance.


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