Solarmeter® Model 6.5 UV Index Meter
The instrumentation used to measure UV index for the U.S. E.P.A./NWS program is directed toward the sky in a global normal (perpendicular to level ground) inclination. Therefore the Solarmeter® Model 6.5 is designed to operate in the same fashion. Solar irradiance measured this way includes direct (reduced by cosine law depending on solar zenith angle) plus diffuse (diffused by the atmosphere).
Proper usage of Solarmeter Ultraviolet Radiometer for Outdoor UV Index Measurement
The instrumentation used to measure UV index for the U.S. E.P.A./NWS program is directed toward the sky in a global normal (perpendicular to level ground) inclination. Therefore the Solarmeter® Model 6.5 is designed to operate in the same fashion. Solar irradiance measured this way includes direct (reduced by cosine law depending on solar zenith angle) plus diffuse (diffused by the atmosphere).
This vertical (global) reading represents an average intensity value your body will experience while being active on a tennis or volleyball court, or lying flat on a blanket on the grass. If however, you are reclined in a lounge chair facing the sun perpendicular to the sun angle, you will experience a higher UV intensity, as represented by pointing the Solarmeter ® directly at the sun. This value will typically exceed the actual UV index number.
Sensor
Silicon Carbide (SiC) Photodiode under UV glass window, hermetically sealed with Eeff (erythemally effective) filter and diffuser cap.
To obtain the UV index instantaneous value, the following instructions will provide the most consistent, accurate results:
Stand clear of buildings, trees, etc. to obtain a “full sky” field of view.
Hold the meter vertical out in front of your body.
Press and hold button on front of meter case. Note reading on LCD. This value represents the instantaneous UV index.
The highest UVI values typically occur when the sky is a deep blue color, and sometimes when the sun is between scattered white “puffy” clouds. Take extra precaution under these conditions to reduce sunburn potential.
Note that various cloud and haze conditions reduce the UV index. When partly cloudy, take readings often and average clear with cloudy readings to correlate with actual UV index. Take care in hazy or slightly overcast conditions because although the direct UV reads less than when sky is clear, the diffuse UV can be higher… as seen by pointing the meter in various directions.
Long Term Stability
The graph to the right shows how two different Model 6.5 UV Index meters preformed over a 6-year period 1999-2005… at low to very high UVI values. Linear regression R² is 0.992. This data is courtesy of:
Forrest M. Mims IIIGeronimo Creek Observatorywww.forrestmims.org
