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2. Lumen (unit) - Wikipedia

   en.wikipedia.org/wiki/Lumen_(unit)

   The lumen (symbol: lm) is the unit of luminous flux, a measure of the perceived power of visible light emitted by a source, in the International System of Units (SI). Luminous flux differs from power ( radiant flux ), which encompasses all electromagnetic waves emitted, including non-visible ones such as thermal radiation ( infrared ).

3. Luminous efficacy - Wikipedia

   en.wikipedia.org/wiki/Luminous_efficacy

   Luminous efficacy can be normalized by the maximum possible luminous efficacy to a dimensionless quantity called luminous efficiency.The distinction between efficacy and efficiency is not always carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed in lumens per watt, or "efficacies" expressed as a percentage.

4. Luminous intensity - Wikipedia

   en.wikipedia.org/wiki/Luminous_intensity

   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.

5. Luminous flux - Wikipedia

   en.wikipedia.org/wiki/Luminous_flux

   The luminous intensity (in candelas) is a measure of how bright the beam in a particular direction is. 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 ...

6. Orders of magnitude (illuminance) - Wikipedia

   en.wikipedia.org/wiki/Orders_of_magnitude...

   Factor ()Multiple Value Item 0 0 lux 0 lux Absolute darkness 10 −4: 100 microlux 100 microlux: Starlight overcast moonless night sky [1]: 140 microlux: Venus at brightest [1]: 200 microlux

7. Candela - Wikipedia

   en.wikipedia.org/wiki/Candela

   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.