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Luminous intensity is the radiating power of a source of light in a particular direction, weighted with the spectral sensitivity of the eye. Measuring luminous intensity in candela (English Candela) over the entire solid angle in Sterad (SR), one receives the light-current in lumens (lm).
One would have to line up now 12.566 of such segments to become a sphere again.
A LED with an angle of e.g. only 20°, possesses a SR of 0,0955 and one would have line up 132 such LEDs, like a ball together to get the full angle! (look at our table)
Where does our luminous intensity (CD) remain now?
The unit of luminous intensity results now from the quotient too lm:sr (Lumen/Steradiant).
With our example, the candle sends 12 lm into all directions in space(360°). For an angle of 65°(1sr) there is only 1 CD (12:12=1) left.
To better understanding, another example:
If we now would pencil the light-current of the candel(12 lm) by a parabol mirrors to our 1m² surface (on an angle of 65°=1sr), then our candle would have on times a luminous intensity of 12 CD!
Isotrope Sources of light (Bulbs, candle) radiates their light in all directions in space.
Anisotrope Sources of light (LEDs) radiates their light in a solid angle. In the example with the parabol mirror, we made form an anisotropic an isotropic source of light.
Opening angle: | 180° | 90° | 65,55° | 60° | 50° | 45° | 40° | 30° | 20° | 15° | 10° | 1° |
Parts of the sphere | 2 | 6,8 | 12,566 | 15 | 21 | 26 | 33 | 59 | 132 | 234 | 526 | 52525 |
sr Factor | 6,28 | 1,84 | 1,00 | 0,842 | 0,589 | 0,478 | 0,379 | 0,214 | 0,0955 | 0,0538 | 0,0239 | 0,00024 |
Öffnungswinkel: | 180° | 170° | 160° | 150° | 140° | 130° | 120° | 110° | 100° | 95° | 90° | 85° | 80° | 75° | |
sr Faktor | 6,2832 | 5,7356 | 5,1921 | 4,6570 | 4,1342 | 3,6278 | 3,1416 | 2,6793 | 2,2444 | 2,0383 | 1,8403 | 1,6507 | 1,4700 | 1,2984 | |
Öffnungswinkel: | 70° | 65,55° | 60° | 55° | 50° | 45° | 40° | 35° | 30° | 25° | 20° | 15° | 10° | 5° | 1° |
sr Faktor | 1,1363 | 1,0003 | 0,8418 | 0,7099 | 0,5887 | 0,4783 | 0,3789 | 0,2908 | 0,2141 | 0,1489 | 0,0955 | 0,0538 | 0,0239 | 0,0060 | 0,00024 |
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