Campbell Scientific SP-LITE Solar Radiation Sensor - Manual (Page 5)

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SP-LITE Silicon Pyranometer
The SP-LITE measures incoming solar radiation (sun plus sky radiation) with a photodiode
detector. Output from the photodiode is a current, which is converted to voltage by an
internal shunt resistor. The SP-LITE can be used in solar energy applications such as
plant growth, thermal convection and evapotranspiration.
1. General Description
FIGURE 1. SP-LITE Sensor without Leveling Fixture
The SP-LITE is used for measuring solar radiation. It measures the solar
energy received from the entire hemisphere – i.e. 18
0° field of view. The
output is expressed in Watts per square meter (W m -2 ).
The SP-LITE is designed for continuous outside use, and its calibration is valid
only for unshaded natural daylight – not for artificial light. It is most usually
used to measure solar radiation being received on the horizontal plane.
However, the SP-LITE can, if required, be used in an inverted or tilted
position.
1.1 Electrical Properties
The SP-LITE consists of a photodiode complete with housing and cable. The
circuit includes a shunt resistor for the photodiode in order to generate a
voltage output. The electrical specification of the sensor is determined by the
characteristics of the photodiode and resistor. The electrical circuit of the
pyranometer is shown in Figure 2, below.
The electrical sensitivity of the photodiode changes with temperature. A
nominal value for this change is 0.2% change per °C. Calibration is carried out
at 20 °C.