Radiant energy – Invisible radiant energy responsive electric signalling – Ultraviolet light responsive means
Reexamination Certificate
1999-08-25
2002-09-17
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Ultraviolet light responsive means
C250S338100, C250S461200
Reexamination Certificate
active
06452188
ABSTRACT:
BACKGROUND OF THE INVENTION
Migration has resulted in large populations living in areas with sunlight environments not suited to their skin type. Migration toward the equator has resulted in light skin persons with difficulty in avoiding overexposure with sunburns and increased risk of skin cancer. Migration away from the equatorial regions has resulted in dark skin persons with difficulty in getting enough sunlight exposure in the wintertime to avoid vitamin D deficiency and associated health problems. Many light skin persons and especially older persons also incur problems with vitamin D deficiency.
One specific problem is the difficulty in knowing how long an individual can be exposed to outdoor sunlight without having a later development of red skin or a painful burn. The problem is particularly severe for young children who have not developed a general knowledge of their tolerance to sunlight in the spring and early summer. Public surveys of the response to the ultraviolet index predictions of the National Weather Service have resulted in a desire for further information such as burn time, Geller. Skin damage time, a term often used rather than burn time, varies so greatly from individual to individual that skin damage time data for a reference skin type is of very limited usefulness.
A second problem is knowing how long an individual needs to be exposed to sunlight for good health. There are many beneficial effects of sunlight exposure. The Health Council of the Netherlands estimated the yearly minimum dose to be 55 MED for an average of 0.15 MED per day, World Health Organization EHC-160, page 131. Avoidance of reddened skin at a dose of 1 MED leaves a relatively small ratio of sunburn dose to minimum dose of slightly less than 7 to 1 (1/0.15).
In addition to just avoiding skin reddening, many high ultraviolet radiation doses greatly increase the risk of skin cancer. Tests with hairless mice at an ultraviolet irradiance of about 0.7 MED 5 days/week for 11 weeks lead to 90% of animals with tumors by week 34, Black 1995. Many persons avoid sunlight to reduce the risk of skin cancer, however too little ultraviolet radiation can result in insufficient vitamin D which is believed to increase the risk of cancer, Garland and risk of high blood pressure, heart disease and other conditions of decreased health, Kime.
The limits for too much and too little ultraviolet erythemal radiation vary from individual to individual depending on factors including the darkness of the skin, age, diet, and other conditions affecting tolerance to ultraviolet radiation exposure. The exposure of a dark skin individual necessary to produce vitamin D levels sufficient to reduce the risk of cancer (as estimated by Garland) can be greater than six times the exposure needed by a light skin individual, Holick 1985. Age is a significant factor in the formation of previtamin D in the skin by sunlight. Skin samples of 8 and 18 year old subjects produced two to three times as much previtamin D as skin samples of 77 and 82 year old subjects when exposed to simulated solar radiation, Chen. Older persons do not produce as much circulating 25-OH vitamin D as young persons when exposed to whole body irradiation by ultraviolet light, Chen. Most of the skin areas gradually darken with age, Lock-Anderson, making it increasingly difficult to obtain sufficient sunlight exposure for vitamin D formation at older ages during the winter.
During the spring and summer light skin persons are often susceptible to overexposure. Avoidance of exposure for long periods outdoors or use of sunscreen lotion, protective clothing and a broad brim hat are wise choices for an individual under this condition, Long. The development of a tan can increase the MED and corresponding outdoor exposure tolerance with longer burn time, Fitzpatrick 1972, p755. The term burn associated with sunburn is histologically different than a thermal burn, however, many of the clinical symptoms are similar, Urbach.
Daily doses much less than one MED over long periods of time are desirable to maintain a low risk of skin cancer. As shown by Blum in tests with animals, carcinogenesis is closely dose dependent for moderate and high dose rates. However, for low dose rates, carcinogenesis is greatly reduced. Low ultraviolet dose rates such as 0.15 MED are desirable to reduce the risk of skin cancer. The body can repair much of the DNA damage due to many factors including the presence of free radicals and exposure to ultraviolet radiation, Shigenaga. Low daily ultraviolet radiation doses rates are necessary so the number of damage sites will be within the daily repair capability of the body as limited by other factors such as diet.
An estimate of the dose that corresponds to one MED for an individual is sometimes based on the sunburn tendency such as always, usually, sometimes or rarely. However, this results in wide range estimates subject to large error. An improved technique is desirable.
Solar Radiation Enviroment
The solar radiation environment is predicted daily by the National Weather Service and it can be measured by commercial cards and meters. Also environmental models predict the average environment by time of the year and location.
Solar radiation ultraviolet index (UVI) daily predictions to aid in avoiding solar ultraviolet radiation overexposure now available from the National Weather Service have been criticized since individuals cannot easily determine how long they can be exposed outdoors on bright spring and summer days without getting a sunburn, Geller. The ultraviolet index unit corresponds to 25 milliwatts/square meter for the erythemally weighted dose rate unit, Long. This factor along with the UVI, and an individual's MED (typical units: mJ/cm
2
) enable the calculation of the burn time. The primary problem is the estimation of an individual's MED. In addition to the problem of determining the burn time for light skin individuals, a method for determining the time for sufficient light exposure for dark skinned individuals is not generally available and utilized.
In Philadelphia, the Solar Light Company maintains a website with daily values of the minimum erythemal dose (MED) for half hour periods for a type II individual. Erythemal refers to reddening. Skin damage times can be evaluated for an average type II individual using this type of data or National Weather Service UVI data to avoid excessive daily sun exposure. As an example on Jul. 18, 1998 at 12:00 the dose rate in Philadelphia was 1.7 MED's per half hour period. The skin damage time for 1 MED was 30 minutes/1.7 which is just under 18 minutes for a type II individual having an MED of 21 mJ/cm
2
.
In using the daily solar radiation ultraviolet data one problem is how do individuals determine their sensitivity ratio relative to an average type II individual or their sensitivity (MED). The relative sensitivity or MED is necessary so they can estimate their own or their children's safe exposure time and avoid sunburns yet obtain sufficient light necessary for beneficial effects.
In addition to the daily solar radiation predictions by the National Weather Service and the Solar Light Company daily reports, two models predict the average solar radiation environment for the different times of the year. Madronich evaluated the daily solar radiation for clear days for different months at different latitudes. The values can be used to estimate the average daily erythemal exposure for clear days. A model of global ultraviolet radiation including local atmospheric conditions and surface elevation was generated by Sabziparvar. The values can be used to estimate the average daily erythemal exposure including the effects of clouds rather than just for clear days. The clear day values of Madronich's model are useful for determining exposure limits for avoidance of overexposure on clear days. The values of Sabziparvar's model for average days including effects of clouds is useful for determining the necessary exposure to avoid underexposure and possible vitamin D defici
cummings Henry W.
Hannaher Constantine
Israel Andrew
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