In retrofit CFLs or LEDs, and even energy-saving halogen lamps, an equivalent incandescent or halogen wattage is given by manufacturers to make life easier. Now that different technologies have entered into the equation, using wattage as an indicator of output has become increasingly obsolete. With incandescent and halogen lighting it was always easy to equate wattage with light output, because the same wattage always produced the same amount of light. This means it contributes to candela just as it contributes to lux at X meters away.Lumen (lm), lux (lx) and candela (cd) are units of measurement used to describe the output of bulbs and light fittings. The spill also follows the inverse square law of light. Third, it is not possible for candela numbers to "be inflated by spill" If you want to know the intensity at 20m then you just do candela / 20^2 = 250 lux So there is nothing wrong comparing lights using the candela value. If a flashlight measured 1000lux at 10m that flashlight is said to have 100k lux at 1m aka 100kcd Second, since candela is literally just a recalculation of the lux, you can convert between the two units whenever you want and they will not change. The lumens and candelas produced by the bulb don't change, but the number of lux entering your eyeball goes way down when you're 100 yards from the bulb.īrightness is perception of light, not an inherent property of any light source.Īnd what kind of hellish combat zones are people living in that they have to go out armed?Ĭlick to expand.Candela numbers are not inflated by spill.įirst of all, nobody measured candela by putting the luxmeter at 1m and taking a measurement, you have to go 10-20m away and take a measurement and then use the inverse square law of light to calculate it back to 1m to get candela.Ī) luxmeters have a limited measurement range that usually only goes up to 20k or 200k lux so you need to be farther away to actually get a measurementī) luxmeters lose precision when measuring higher lux values so again you want to go farther away to have a more accurate lower lux numberĬ) depending on the head diameter of the flashlight the beam is usually not fully formed at 1m, that means the luxmeter will not be reading the full intensity of the flashlight But if that same 1000 watt lamp is the only light working in an entire mall parking lot, it's going to be spooky dim when you're more than a short distance away from it. Stare into a 1000 watt mercury vapor lamp at arm's length, it'll make your eyes water, (because it's so "bright"). Lots of lumens, but spread out - lower candelas, and each surface in the room gets a lower lux share. An old-timey frosted 100 watt incandescent bulb will fill a residential room with comfortable light levels, but the cat will easily spot the laser pointer dot anywhere on the floor. That's like a laser - lots of candelas (intensity) but not much total light power (lumens). You could have a narrow pipe going up a hill to a spring - at the bottom, you'd have lots of pressure, but maybe not much water in the pipe. It's like "gallons" - how much water in the pool? "feet" - how deep is the pool at any point? "gallons per square foot" - how many walls can I cover with this can of paint? Candela - how much power is passing through a point LUx - how much total light power is falling on an area. Measuring light is no harder than measuring liquids. The problem is that we mean so many different things by "brightness" when we use that term, that it's hard to relate that sensation to the numerical measurements.
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