UV-A Measurements and Spectral Errors
Apogee Instruments model SU-200 UV-A sensors are calibrated to measure ultraviolet radiation from the sun
between 315 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)
Expected EFD Error [%]
Expected PFD Error [%]
Clear Sky
0.0
0.0
Overcast
0.0
-1.1
Direct Normal
-0.2
-1.0
Diffused Blue Light
0.3
1.4
CWF T5
8.2
9.2
Metal Halide
1.2
-1.2
Quartz Halogen
-2.3
-3.8
Mercury Arc
16.2
16.9
T12 Fluorescent UV-A Enhanced
12.2
15.2
UV-A LED (365 nm Peak)
37.4
35.3
UV-A LED (386 nm Peak)
1.8
-3.9
UV-A LED (395 nm Peak)
-36.9
-41.2
