Tuesday, April 28, 2009

Photometric meters

1. Goniophotometer [1]
The Greek word "gonio" means angle. A goniophotometer measures spatial distribution (xyz and angular) of a radiation source. It has a built-in photopic [2] filter so all measured radiometric quantities automatically convert to photometric ones after calibration. A goniophotometer is able to measure:

  • Luminous power (flux) in lm.

  • Luminous intensity in cd = lm/Sr.

  • Illuminance in lux = lm/m2.

  • Luminance in cd/m2 = lm/m2-Sr.

  • Color coordinates and correlated color temperature.

  • Sample's retro-reflection as function of angle in cd/lx.


2. Colorimeter [3]
There are also filters in a colorimeter to mimic the human cone response. A colorimeter produces numerical results in one of the CIE color models.

References and notes:
[1] X-Rite GmbH - Optronik catalog.
[2] The word "photopic" refers to vision by cone receptors in the human eye (while "scotopic" refers to rod receptors).
[3] Bruce Fraser, Chris Murphy, and Fred Bunting, Real World Color Management, 2nd ed. Peachpit Press 2005. Page 43.

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