The assertion “People wearing the UVA+UVB watch would learn to keep out of the hottest portion of the sun (which actually has the vitamin D) because their watch would (falsely) tell them that they would get lots of vitamin D is the late afternoon - when it is not as hot” is totally misguided and erroneous and should be taken off your web page.
There is substantial international agreement (many references in the literature) to report UV using the erythemally weighted radiation (UVEry), rather than in terms of UVB.
where λ is the wavelength in nm, I(λ) is the irradiance in W m**2 between 250 and 400 nm and w(λ) is the erythemal weighting function. The weighting function is unity at wavelengths of 298 nm and less. As the wavelength increases above 298 nm, it decreases throughout the UVB and UVA range. SunFriend uses weighting function algorithms with the measured radiance to calculate the UV Index (UVI). Using the measured UVI SunFriend calculates the exposure time to induce erythema, the time taken to induce 1 MED skin damage, for a given skin sensitivity. Since SunFriend is taking readings continuously the exposure time is being continuously updated. SunFriend alerts the user to get out of the sun or to take protective measures once the recommended exposure time, for a particular skin sensitivity, has been reached.
SunFriend allows the user to take advantage of the time of day when UVB levels are highest (usually between 12 noon and 2pm or solar elevation angle greater than 50 degrees and depending on cloud conditions) for their latitude and longitude location by ENSURING that they do not get erythemal damage. The user will optimize vitamin D production during the time when the UVB component of the suns radiation is highest but without burning themselves.
SunFriend recommends that the user consults a website like:
to find out what time of the day, for their particular location, the sun elevation angle is greater than 50 degrees and to use that time to take the health benefits of UVB radiation, while knowing that SunFriend will give an alert to when the user has reached their maximum allowable radiation dose (www.icnirp.org). Please contact us if you have any questions or need further clarification.
SunFriend Corporation Md., USA www.sunfriend.com
“One pill every two weeks fights diabetes, cancers, heart failure, and 18 other diseases.”
There is substantial international agreement (many references in the literature) to report UV using the erythemally weighted radiation (UVEry), rather than in terms of UVB.
The erythemally weighted UV is:
UVEry = IntegrationI(λ)w(λ) dλ
where λ is the wavelength in nm, I(λ) is the irradiance in W m**2 between 250 and 400 nm and w(λ) is the erythemal weighting function. The weighting function is unity at wavelengths of 298 nm and less. As the wavelength increases above 298 nm, it decreases throughout the UVB and UVA range. SunFriend uses weighting function algorithms with the measured radiance to calculate the UV Index (UVI). Using the measured UVI SunFriend calculates the exposure time to induce erythema, the time taken to induce 1 MED skin damage, for a given skin sensitivity. Since SunFriend is taking readings continuously the exposure time is being continuously updated. SunFriend alerts the user to get out of the sun or to take protective measures once the recommended exposure time, for a particular skin sensitivity, has been reached.
SunFriend allows the user to take advantage of the time of day when UVB levels are highest (usually between 12 noon and 2pm or solar elevation angle greater than 50 degrees and depending on cloud conditions) for their latitude and longitude location by ENSURING that they do not get erythemal damage. The user will optimize vitamin D production during the time when the UVB component of the suns radiation is highest but without burning themselves.
SunFriend recommends that the user consults a website like:
http://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html
to find out what time of the day, for their particular location, the sun elevation angle is greater than 50 degrees and to use that time to take the health benefits of UVB radiation, while knowing that SunFriend will give an alert to when the user has reached their maximum allowable radiation dose (www.icnirp.org). Please contact us if you have any questions or need further clarification.
SunFriend Corporation
Md., USA
www.sunfriend.com