Light

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Light Output Measurements

Lumens

Lumens are a measure of the total output from a light source. For a flashlight lumens can be measured "at the emitter" or "out the front." Emitter lumens are all of the light emitted by the source (LED or bulb). Out the front lumens are those that bounce off the reflector or go directly out the front, and make it through the lens, so they are always less than emitter lumens. When a LED manufacturer rates a LED, they will use lumens of output measured at a certain electrical current (e.g. 350mA). The manufacturer will use emitter lumens since they are measuring a bare emitter. Some flashlight manufacturers (particularly budget brands) will quote those emitter values instead of providing actual out the front lumen values. The most reputable manufacturers seem to underrate the lumen output, therefore a high end SureFire lumen is brighter than an budget Ultrafire lumen usually.

In order to measure lumens from a flashlight, a calibrated lightbox is required. Lumen values are measured and compiled on CPF in the LED Flashlights Forum] under a stickied post by MrGman. Because very few people have calibrated integration spheres to properly measure lumens, many reviewers will use uncalibrated light boxes and create output graphs with readings in units other than lumens (for instance, the voltage coming off of a solar cell or a reading from a light meter somewhere in the light box) or just set a value to 100% for that light when it is first turned on and at its brightest. This still results in good information about how the light performs over time as the battery draws down and the LED becomes hotter and provides less output. It is also useful in comparing different brightness levels that a flashlight may have. A good lightbox will evenly distribute light so that whether a flashlight has a very tight hotspot or is all flood, the reading will still reflect overall light output.

Lux

Lux is a reading of light intensity at a particular spot where a light reading is taken. Close to the light source, the value will be higher and drop off the further the reading is taken from the light. Likewise, the reading will be higher in the hotspot of a flashlight beam than it is in the less bright spill. The good thing about lux is that all it takes is a light meter to get a reading, which is much easier than lumen measurements. Lux readings are also good in measuring the throw of a light. Reviewers can do comparisons of different light by measuring the lux close to a light and then a certain distance from the light to arrive at some value for effective throw.


MSCP (mean spherical candlepower)

MSCP is just another measurement of total light output. MSCP times 4 times pi = Lumens.

Candlepower

Candlepower measures the intensity of a light source at a single point a given distance from the source.

You cannot convert from candlepower to lumens. It's like the difference between pomegranates and watermelons - with one, you eat the seeds and throw away the flesh, and with the other, you eat the flesh and throw away the seeds.


There are a number of units for measuring intensity:

cd - candellas (Candlepower)

mcd - millicandellas

Most flashlights will be measured in Lumens or Lux. The large spotlights are measured in cp. The strobe lights on fire alarms are always measured in candelas. ADA (Americans with Disabilities Act) requires a fire alarm strobe to be 15cd at 45degrees and 75cd on-axis.

Optics

Almost all flashlights have some sort of optics, being a reflector or collimator, or possibly a combination of the two if there is more than one light source. A few lights have recessed LEDs, that are surrounded by the flashlight body material, and feature no reflector(s) or collimator(s). But generally speaking, you will find at least one of the following two types of optics in flashlights.

Reflectors

=Reflectors are the most commonly found type of optics for flashlights. They have a polished metal finish on them, and they reflect the light from the light source towards the target. Some are made smooth, and others are dimpled/stippled. The dimpled ones usually offer smoother beam patterns and come in higher quality lights, whereas the smooth ones have rougher looking beam patterns which aren't quite as nice. A few examples of reflectors are the IMS S017XA, S027XA, S020XA, and McFlood.

Collimators

=Collimators are used only with LEDs, and they are clear plastic. They refract the light to adjust the beam. Both types of optics offer advantages and disadvantages, and people have different preferences. It also depends on the type of application. Examples of names of collimators are 30mm, Fraen, Fraen 30ยบ, Fraen-LP (low-profile), NX-01, and NX-05.

Inova X0 disassembly

Color Vision

Big warning: much content of this page needs to be verified!

This page intends to collect knowledge on the how and why of color in flashlights.

Flashlights can provide color in the form of specific LEDs, or by use of filters.

There is lots of confusion on the use of color in flashlights

  • most colors won't allow a correct reading of maps: for example, red light will hide red symbols on maps, same problem for blue (and green will hide the vegetation symbols!). (see also here)
  • blue is not so much special to "highlight" (actually blacken) dried up blood. you need chemicals (which ones?) to get blood light up under UV.

IR

  • for IR scene illumination
  • as beacon

Red

  • to reduce detection by others
  • will best preserve night vision
  • Wavelengths beyond 610nm will not destroy NV
  • note: NVIS is sensitive to orange->near IR light

See also

Yellow / Amber

Green

I'd like to know why green is interesting. According to e.g. Streamlight Sidewinder, it can be used for hunting? Animals would not see green? --axd 04:44, 13 April 2009 (MDT) (cleared to remove this line)

  • the eye is most sensitive to green
  • details will be more easily viewed in Light Amplification devices. Note that such devices have filters to remove (narrow bands of?) green light (Dichroic filter?) (to avoid being blinded by buddy NVG light?) (see also Patent)

Blue

Copied from http://www.xenopuselectronix.com/xeled/BloodTracker.html:

Technical note: This is not a UV product. Blood does not fluoresce under UV (unless separated unto plasma). Blood looks black under Blue, Near-UV, and UV. Blood absorbs Blue, Near-UV, and UV.

Medical uses?

INTERESTING BUT TO CONFIRM

Skin

Mood

Sleep

Light therapy

UV

See also

See also

CPF

Other

Ads that explain choice of colors


To add in separate Wiki pages?

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