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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