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30 cd/m 2: Green electroluminescent source [5] 10 2: 55 cd/m 2: Standard SMPTE cinema screen luminance [10] 80 cd/m 2: Monitor white in the sRGB reference viewing environment 250 cd/m 2: Peak luminance of a typical LCD monitor [11] [12] 700 cd/m 2: Typical photographic scene on overcast day [7] [9] [12] 10 3: kcd/m 2: 1 kcd/m 2: Cloudy sky at ...
The guide number here (full power setting, ISO 100, and normal-angle coverage) is 37 for calculations made in meters (yellow arrow) and 120 for feet (orange). For instance, on the foot scale, f /4 × 30 ft = 120, as do both f /8 × 15 ft and f /16 × 7.5 ft. In meters, f /1.4 × 26 m = 37 as do f /22 × 1.7 m and every combination between.
If a lamp has a 1 lumen bulb and the optics of the lamp are set up to focus the light evenly into a 1 steradian beam, then the beam would have a luminous intensity of 1 candela. If the optics were changed to concentrate the beam into 1/2 steradian then the source would have a luminous intensity of 2 candela.
In the US lighting industry, foot-candles are a common unit of measurement used by architects to calculate adequate lighting levels. Foot-candles are also commonly used in the museum and gallery fields in the US, where lighting levels must be carefully controlled to conserve light-sensitive objects such as prints, photographs, and paintings, the colors of which fade when exposed to bright ...
By comparison, a 60-watt household incandescent lamp will produce about 900 lumens. The luminous efficacy or lumens produced per watt of input of flashlight bulbs varies over the approximate range of 8 to 22 lumens/watt, depending on the size of the bulb and the fill gas, with halogen-filled 12-volt lamps having the highest efficiency.
A 25 W compact fluorescent light bulb puts out around 1700 lumens; if that light is radiated equally in all directions (i.e. over 4 π steradians), it will have an intensity of = / = . Focused into a 20° beam (0.095 steradians), the same light bulb would have an intensity of around 18,000 cd or 18 kcd within the beam.
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