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Light
Measurement*:
Your light
is bright as H*** or it's not, that is the
best measurement.
All light measurements can be traced back
to the Candela, which is the unit of
luminous intensity. The Candela is also
sometimes called candlepower, and is
similar to an older unit, the candle,
which was based upon an actual candle of
specified dimensions and construction.
There are two basic methods used by
various flashlight manufacturers to rate
the light output of their products.
Total Luminous Output may be expressed in
candela or in
lumens. This is a
measure of the entire light output of the
flashlight regardless of beam focus. It is
almost solely a function of the lamp, and
for practical purposes is equal to the
lamp output which lamp manufacturers rate
in Mean Spherical Candela (Sometimes
called Mean Spherical Candlepower which is
not the same as peak beam candlepower), or
in lumens. Multiply candela by 12.57 to
convert to lumens. For example, the 20
watt lamp used in the SL-35X™ is rated at
450 lumens or 35.8 Mean Spherical Candela.
Peak Beam
Candlepower is a measure
of the brightest spot in the focused beam.
It is a function of both the output of the
lamp and the efficiency of the reflector.
The focused spot of light has the same
intensity that a bare source of unfocused
light of the same candlepower would
produce on the same area from the same
distance. For example, a flashlight of
20,000 beam candlepower would project,
within its "hot spot," the same amount of
light on a wall as would a bare lamp of
20,000 candela at the same distance.
Typical values of beam candlepower will
run into the tens of thousands for
powerful rechargeable flashlights.
Since the
Total Output system does not take into
account the focusing efficiency of the
reflector, there is no way to convert
between peak beam candlepower and lumens.
Additionally, all light rating systems
depend on the perception of the human eye
and are therefore subjective. Another
important factor besides absolute
intensity is the whiteness (technically
the Color Temperature) of the light
source. If two equally intense light
sources differ in color temperature, the
eye will perceive the whiter source
(higher color temperature) to be brighter
than the more yellow one. Color
temperature is expressed in degrees on the
Kelvin scale. A very white flashlight lamp
will be rated around 3200 K.*
*Streamlight, "Information
about how the brightness of a light
(luminosity) is measured.", http://www.streamlight.com/releases/light_measurement.htm
(accessed January 25, 2005).
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Candlepower vs Lumens
Peak beam candlepower is the measure of
the brightest spot in the beam and is a
function of both the output of the lamp
and the efficiency of the reflector. As a
result, peak beam candlepower is a
subjective measurement, and different
flashlight manufacturers measure it
differently. Therefore, comparing peak
beam candlepower ratings of flashlights
from various manufacturers will not give
an accurate comparison of brightness.
On the other hand, lumens can be used when
comparing brightness because it is a
measurement of the entire light output
regardless of beam focus.
Since peak
beam candlepower is a measure of the
reflected light, there is no way to
convert peak beam candlepower into lumens. |
LED
FAQs:
 What
is an LED? LED stands for Light Emitting
Diode. In its essence it produces light in
a whole different way than a light bulb.
We'll spare you all the nerdy techno
babble, but here is how it works in a
nutshell. The idea for the light bulb is
100 years old. Thomas Edison figured he
could make a metal wire glow once he
sealed it into a bulb filled with a
special gas. Light bulbs are very
inefficient producers of light and have
hardly evolved over the last century.
Notice how hot they get? They can turn
more than 90% of the consumed energy into
heat. In fact it is this heat build-up
that eventually destroys the light bulb by
burning up the wire filament. An LED has a
tiny solid-state crystal that is steered
with a low voltage. It glows by utilizing
virtually all consumed energy for light
production. Feel the LEDs on your
flashlight and you'll see they won't get
hot. In reality this means you can use our
SLED flashlights 30-70x longer on one set
of batteries than an old-fashioned krypton
flashlight. |
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Flashlight
FAQS