Sun exposure monitoring device

Details Sun exposure monitoring device Sun exposure monitoring device

1991-08-23

1993-03-23

Howell, Janice A.

Radiant energy

Invisible radiant energy responsive electric signalling

Ultraviolet light responsive means

2504581, G01J 158

Patent

active

051967057

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the monitoring of exposure to sunlight, and is particularly directed at the provision of a device which measures the power of incident sunlight. It is intended for use by sunbathers to assist in monitoring safe exposure levels, and thereby minimise damage to the skin.
The human skin responds to incident sunlight by turning red (erythema), developing a tan (melanogenesis) and developing cancers. This invention makes no reference to carcinogenic effects, and is primarily concerned with the development of erythema. Exposure to ultraviolet light, principally in the region 280-400 mm causes erythema, the visible effects of which normally become apparent around 8 hours after exposure, and which peaks around 72 hours after exposure. Although the sensitivity of normal skin to ultraviolet in this wavelength range varies widely, an international standard for this sensitivity has been proposed. This is based on the concept of a minimum erythemal dose (MED); i.e., the dose that is sufficient to provoke perceptible reddening, or erythema, and is described in a research note published in the CIE Journal Vol 6 Number 1 of 1987, on pages 17-22. The standard is referred to as the relative erythemal action spectrum, and is tabulated as follows;


______________________________________ Wavelength Erythemal effectiveness nm Relative ______________________________________ 250-298 1.0 300 0.65 310 0.074 320 0.0086 330 0.0014 340 9.7e-4 350 6.8e-4 360 4.8e-4 370 3.4e-4 380 2.4e-4 390 1.7e-4 400 1.2e-4 ______________________________________
The above table assumes a uniform erythemal sensitivity to ultraviolet light in the wavelength range 250-298. The reasons for this are discussed in the research note referred to above. The figures given are based on research on untanned white torso skin, and for the skin type that was the basis of the table the MED is calculated to be 200-400 Joules/m.sup.2 at a wavelength of 300 nm. The sensitivity at other wavelengths can be found by dividing this figure by the entries in the table. The table thus enables the generation of a relative erythemal action spectrum, and this is shown in the note on page 20 of the CIE journal. Other skin types will have different MEDs, and it should be recognised that the MED of a particular individual can be effected by a number of external factors. Particularly, after recovery from a first exposure, a given skin type can more readily tolerate an increased second dose of exposure.
An equivalent tabulation for sensitivity to tanning (melanogenesis) is believed to be broadly similar. It is understood that the principal difference is a greater tanning sensitivity at longer wavelengths.
The present invention is concerned with the measurement of the power of natural sunlight in circumstances where burning is likely. Because of the relatively low power of erythemally active ultraviolet light in relation to the power at nearby and other wavelengths, accurate measurement is difficult. Various devices have been developed to isolate and measure the power of the ultraviolet content in sunlight, but with varying degrees of success. Generally, these devices employ one or more filters, and either measure the power of ultraviolet transmission through an UV pass filter, or calculate a power measurement by subtracting the power generated from a transmission through an UV stop filter from a power measurement from unfiltered light. The advantage of the latter technique is that UV stop filters are less expensive than UV pass filters. Reference is also directed to International Patent publication No. WO88/06279 in which a radiation detector is disclosed comprising a photoluminescent element of thin section. While this detector can monitor radiation received by the element, it cannot discriminate between higher and lower risks of burning. In each case, power measurement is usually accomplished using a photosensor such as a photodiode. They can be adapted to measure an instantaneous power level, or integrated to give a measuremen

REFERENCES:
patent: 4096387 (1978-06-01), Buckley
patent: 4262206 (1981-04-01), Viehmann
patent: 4935631 (1990-06-01), Mosley et al.

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