Campbell Scientific SP-LITE Solar Radiation Sensor - Manual (Page 7)

SP-LITE Silicon Pyranometer
3
Both the spectral sensitivity and the photodiode sensitivity of the SP-LITE will
change with temperature, and the separate effect of each of these changes
cannot be easily determined.
1.3 Directional/Cosine Response
A perfect cosine response will show maximum sensitivity at an angle of
incidence of zero degrees (perpendicular to the sensor surface) and zero
sensitivity at an angle of incidence of 90 degrees (radiation passing over the
sensor surface). At any angle between 0 and 90 degrees the sensitivity should
be proportional to the cosine of the angle of incidence.
Figure 4 shows the behavior of a typical SP-LITE. The vertical axis shows the
deviation from ideal behavior, expressed in percentage deviation from the ideal
value.
FIGURE 4. Cosine Response of a Typical SP-LITE Pyranometer
In Figure 4, 0 degrees zenith angle equals 90 degrees angle of incidence. The
vertical axis shows the percentage deviation from ideal cosine behavior.