Point light source: Op = Ï D2 Im ... Ï = ^P/d2 fc
Line light source: -$-L = Ï D3/aq Im/— ... Ï = ÀQ /d3 fc
■j - )3 Area light source: = Ï D4/Àn Im/sf ... Ï = ÀQ ^A/d4 fc vi
Note: If you are using this book's DesignDisk, simply insert the values for D, L, and W into the No-Math Menu for , then the data entry pane beside Ln will display the value for An.
In any light source, if the exiting photons radiate outward in every direction (except for a small conical area subtended around the lamp's base) the uninterrupted distribution is the lamp's full-sphere output. An example of this is a bare incandescent bulb mounted in a porcelain socket. But if the lamp is partly enclosed by a reflective housing, a portion of the lamp's output is redirected through the aperture that remains, which makes its unit radiance more intense. This ray concentration is greatest in spotlights that are largely enclosed by parabolic reflectors with mirror surfaces. For example, a searchlight with a parabolic specular reflector that produces a collimated beam of light may have an axial output that is 80 times more intense than the lamp's full-sphere output.
In summary, ray concentration is a function of the portion of a lamp's spherical output that is enclosed by a reflective housing, the housing's geometric profile, and the specularity of the housing's inner surface.
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