E(r) = (1/r^2) * (Phi) * cos[(epsilon)2] / [4 * (pi)] |
Keep detector aperture small enough so as to have it homogeneously (over-)filled; |
cling to the same angle with respect to the source |
If there is a BEAM WAIST, take this waist as starting point for distance measurements |
now you can increase distance r from the ANISOTROPIC point source (or, from the BEAM WAIST) and inverse distance squared law will stay valid |
* If your source is a disk of diameter D and if it is a Lambertian emitter (fig. 4.3.3-c in para. 4.3.3), then the error will be less than 5% if distance r is at least two times D. |
* If your source is a system like search lights or projectors, then better keep distance r equal to or greater than tenfold source diameter D . |
Subject | used in | source |
"fotometrisches Entfernungsgesetz" | text ref. (1) |
R.Baer, "BELEUCHTUNGSTECHNIK GRUNDLAGEN", Verlag Technik Berlin, 1996, p. 30 |