Operation Manual

10/ 2010 BENNING LUXMETER B
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3.6 What is the CIE V(λ) curve?
The photometric system defines light in terms of how it is perceived by the
human eye.Theeye‘ssensitivitydepends on the wavelength or color of the
light. The spectral response of the human eye also changes with light intensity.
Theeyehastwodistinctivespectralresponses,whicharedefinedaccordingto
the brightness of the light entering the eye:
- Photopiclightconditionsresponse(lightadaptedeye):
Defined for light intensity greater than 0.1 lux. In these conditions, the eye
hasapeaksensitivityinthegreenpartofthevisiblespectrum,at555nm
anditis normalizedto1 atthatwavelength, whiletheeye‘s responseto
infraredorultravioletiszero.
- Scotopic light conditions response (dark adapted eye):
Occurs under low light conditions (scotopic) defined for light intensity
between 0.0001 and 0.01 lux. In these conditions, the eye has a peak
sensitivityatabout500nm.
Figure 3: V(λ) curve for both eye responses
The response is named the CIE or V(λ)curveandisdefinedinthedocument
CIE 10527. Sensors in illuminance meters must use special colour filters to
adapt to the response.
1
0.8
0.6
0.4
0.2
380 420 460 500 540 580 620 660
Scotopic
Sensitivity
Wave length, nm
Photopic