I

D J , where T is transmission of the solar radiation protective material at the wavelength X.

Thus, the proposed instrument can be also used to measure of protective properties of various materials (tissues, cremes, etc.) in UVA and UVB ranges.

3. Professional UV radiation meter

The professional UV radiation meter has been developed on the basis of modern microelectronics. It is designed for measurement of intensity and integral dose of UV radiation in UVA and UVB spectral ranges. The instrument allows one to carry out routine measurements of UV radiation dose, information storage during a pre-set time period and its transfer to an external computer using an appropriate interface, and ensures sound indication when the pre-set UV radiation dose threshold is reached in each of its channels.

The UV radiation meter comprises: two detectors of UV radiation with sensitivity spectra corresponding to UVA and UVB spectral ranges; two identical converting amplifiers-converters; a two-channel ADC, microcontroller, memory unit, control board, indicator device, voltage transformer, and an interface for connection with a computer.

The information display device (specifically, an intellectual two-line LCI) indicates the values of intensity and accumulated UV radiation dose simultaneously through two channels, in standard measurement units (W/m2 and J/m2, respectively), and it also indicates the operation mode. For power supply, 3 V voltage is used, and the consumed current is ~20 mA.

It would be interesting to broaden functional possibilities of the professional UV radiation meter. Recently, an assumption has been made that experimentally observed changes in diffuse reflection coefficient [15] and absorption coefficient [16] of human skin under UV irradiation are due to functioning of protection mechanisms against unfavorable effects of irradiation. In this connection, it is proposed to equip the developed professional instrument with an integrating photometric Ulbricht sphere (see Fig.4), which could be used for measurement of transmission and reflection coefficients of light-scattering objects, as well as (using a multi-filter system and calibrated detectors) for determination of spectral dependences of these coefficients by means of special computer processing [17]. The use of the Ulbricht sphere will also allow a more precise determination of SPF for different materials.

It follows from the theory of multiple reflections inside the Ulbricht sphere that illumination of the internal surface of the sphere is equal at all points and is expressed as

4xR 2 1 -p where F is the light flux entering the sphere, R is radius of the sphere, and p is reflection coefficient of the surface of the sphere. To obtain high values of E, p should be sufficiently high. Therefore, internal surface of the sphere is covered with a layer of BaSO4, for which the diffuse reflection coefficient is more than 95% in the UV range.

Figure 4. Scheme of the integrating sphere:

1 - source of UV radiation;

3 - teflon window (a diffusor of special shape);

4 - shielding from directUV rays;

5 - set of UV detectors with light filters;

6 - the integrating sphere.

Figure 4. Scheme of the integrating sphere:

1 - source of UV radiation;

3 - teflon window (a diffusor of special shape);

4 - shielding from directUV rays;

5 - set of UV detectors with light filters;

6 - the integrating sphere.

It would be also interesting to consider the use in a professional dosimeter of the Ulbricht sphere with multi-filter detectors for computer reconstruction of the entire biologically active solar UV spectrum basing on several experimental points. Taking this information into consideration will allow, in turn, more precise determination of SPF. Presently, the sphere and the computer software for reconstruction of the spectrum are in the course of development.

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