Supplement 1.7: Radiation quantities and radiometry      (7/9)

The radiance      ... continued from the previous page

Radiance measurement methods

For measurements, a detector with a known sensitive area and a solid angle limiter, e.g. an aperture, is required. Adding a converging lens to this arrangement results in a significantly higher light intensity.

A detector with an aperture to limit the field of view.

The detector and aperture are arranged at a distance r. The radius of the detector is D, the radius of the aperture is B. $\alpha$ is the maximum possible half-field of view angle.

The signal yield of a detector with an aperture is very low. Much better light yields can be obtained by adding a lens to the arrangement.

A detector with a converging lens and aperture to limit the field of view.

The maximum reception angle $\alpha$ is determined by the lens (with radius L and focal length f) and the aperture at a distance b. The sensitive area of the detector behind the aperture should be large enough so that it does not limit the beam path. The largest possible half-field-of-view angle $\alpha$ results from the image of the aperture B' at a distance b' from the lens.