UV-A Measurements and Spectral Errors
Apogee Instruments model SU-200 UV-A sensors are calibrated to measure ultraviolet radiation from the sun
between 300 and 400 nm in Watts per square meter. In addition to naturally occurring UV-A radiation from the
sun, there are many electric light sources that emit UV-A radiation (e.g., cool white fluorescent, metal halide,
mercury arc, and germicidal lamps). Although the relative wavelengths of UV-A radiation differ among sunlight and
electric lights, the error estimates shown in the table below indicate the SU-200 provides reasonable estimates of
UV-A radiation coming from electric lamps (table provides spectral error estimates for UV-A radiation
measurements from radiation sources other than clear sky solar radiation). For most common lamps, the error is
less than 10 %. The SU-200 is particularly useful for determining the UV-A filtering capacity of the transparent
plastic and glass barriers that are commonly used below electric lamps.
Radiation Source (Error Calculated Relative to Sun, Clear Sky)
SU-200 Series Irradiance Error [%]
Clear Sky
0.0
Overcast
-0.6
Direct Normal
-0.4
Diffused Blue Light
0.5
UV-Enhanced T5 Cool White Fluorescent
-6.4
T5 Cool White Fluorescent
15.0
Metal Halide
-0.6
Mercury Arc
20.5
T12 Fluorescent UV-A Enhanced
12.0
