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.
|Irradiation Range||0-199.9 UV Index
|Response||280-400 nm Diffey Erythemal Action Spectrum|
|Resolution||0.1 UV Index|
|Conversion Rate||3.0 Readings/Sec|
|Display||3.5 Digit LCD|
|Digit Size||0.4 (in) / 10.2 (mm) high|
|Operational Temperature||32°F to 90°F / 0°C to 37.8°C|
|Operational Humidity||5% to 80% RH|
||4.2L x 2.4W x 0.9D (in) / 106.7L x 61W x 22.9D (mm)|
|Weight||4.5 (oz) / 128 (g) Including Battery|
|Power Source||9-Volt DC Battery|
|Agency Approval||CE Mark|
- Peak sunlight response bandwidth: 290-298 nm
- Total solar response: 290-400nm, Diffey
- Display: 3 ½ digit LCD
- Resolution: 0.1 UVI
- Power Source: 9V DC battery
- Accuracy: ±10% ref NIST
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 III
Geronimo Creek Observatory
Interpretation of UV index Relative to Proper Precautions
U.S. EPA website http://www.epa.gov/sunwise/uvindex.html provides an excellent overview of how the UV Index is calculated and typical safety precautions for reducing sunburn risk. It also describes the Sunwise School Program.
This PDF page has detailed information about the UV Index: http://www.epa.gov/sunwise/doc/uviguide.pdf
There are six (6) skin types that range from low UV tolerance to high UV tolerance. They are described here: http://www.dermnetnz.org/reactions/phototype.html If unsure, consult your physician to determine skin type.
|Pale white skin, blue/hazel eyes, blond/red hair||Always burns, does not tan|
|Fair skin, blue eyes||Burns easily, tans poorly|
|Darker white skin||Tans after initial burn|
|Light brown skin||Burns minimally, tans easily|
|Brown skin||Rarely burns, tans darkly easily|
|Dark brown or black skin||Never burns, always tans darkly|
For Type II untanned skin the time to beginning of sunburn, one minimal erythemal dose (MED) at 210 J/m² per MED, can be calculated from the UV Index reading as follows:
Divide the UVI by 2.33 to get MED/hr. Then divide MED/hr into 60 minutes.
Example for an 8.5 UVI reading: 8.5 / 2.33 = 3.65 MED/hr. Then 60 / 3.65 = 16.4 minutes. Since minutes to burn for previously unexposed Types I and II are so short, these types should heed all of the following precautions even at moderate UV index levels.
To reduce the risk of sunburn, skin cancer, and eye damage:
- Minimize sun exposure at midday (10:00 a.m. to 4:00 p.m.)
- Apply sunscreen with SPF-15 or higher to all exposed areas of the body.
- Reapply sunscreen every two hours, even on cloudy days, especially after swimming or perspiring.
- Be aware of reflective surfaces (water, sand, snow) which increase UV exposure.
- Wear clothing that covers the body and shades the face.
- Protect children by keeping them from excessive sun and applying sunscreen frequently to children older than 6 months of age.
- Wear sunglasses that absorb 99-100% of the full UV spectrum when outdoors in bright sun.
Remember, the most important UV damage prevention is to avoid sunburn.
The Solarmeter® Model 6.5 is not a medical instrument, but rather an affordable scientific instrument designed to help you avoid sunburn by providing an instantaneous UV index value.
Among the outdoor variables affecting UV intensity are:
- Seasonality/Sun Zenith Angle
- Reflective Surroundings
- Weather conditions
- Ozone Layer Thickness
By regularly using the Solarmeter® you will become very informed of damaging UV levels in many and varied conditions. This knowledge, along with following the outdoor precautions mentioned above, should help enable you to avoid sun damage.
Note: Battery operation voltage is 9V down to 6.5V. Below 6.5V the LCD numbers will begin to dim, indicating the need for battery replacement. Under "typical" service load, the battery should last about 2 years.