The Origin of UV-A, B and C

Fred Urbach

ASP Historian (emeritus) & Past-President (Deceased)
Modern phototherapy had its beginning in Copenhagen in 1895 when Dr. Niels Finsen showed the Beneficial Effects of light on tuberculosis of the skin. By 1929 the use of light for the treatment of a variety of diseases had progressed to the point that a first International Congress on "Actinology" was held in Paris. At that time a committee on measurement and standardization of ultraviolet radiation used in medicine was appointed. The second International Congress on Light (Congress Internationale de la Lumiere) was held in Copenhagen in August 1932. The committee reported as follows:

To recommend the standardization of sources used in medicine, dividing the ultraviolet spectrum in three spectral parts, defined provisionally by the following filters:

Noviol-A-Barium-flint (UV of long wavelength UV-A giving approximately the spectral band from 4000 to 3150 Å).

Barium Flint-Pyrex (UV of medium wavelength or UV-B giving approximately the spectral band from 3150 to 2800 Å ).

Pyrex (UV of short wavelength, or UV-C giving approximately the rays shorter than 2800 Å).

For each part of the spectrum, as defined by these filters, the measurement of radiation is to be made radiometrically by means of a non-selective method (e.g., by a thermopile) and preferably (for medical and meteorological measurements) expressed in milligram calories per cm2 per minute.

The lamp manufacturers are advised to give energy data for these parts of the spectrum for all their lamp types, stating all conditions of measurements.

The question whether the specification of dosage should be on a physical or a correlated biological (erythemal) basis was discussed at the first Congress in 1929, and again in the present meeting. But the subject is so new that the physiologists and the phototherapists, who use the erythemal test to gauge the initial dose, could not come to an agreement (Coblentz, 1932).

Comment: The filters described were apparently to be made by Corning Glass Works. At present, Corning does not seem to have any records of these. The argument about whether to use physical or biological units to describe effective dose certainly still continues, even though the subject is hardly new. Lamp manufacturers apparently have not paid attention to recommendations made as long ago as 1932.

Reference

Coblentz, W.W. (1932) Science 76, 412-417.