10/ 2010
BENNING LUXMETER B
21
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
