Evaluation of the anthracene-benzene chemical light meter for ecological research.

The anthracene-benzene chemical light meter is used in ecological studies to measure solar radiation. The meter absorbs only in the ultraviolet (UV) and, in principle, relies on the conversion, by solar UV, of anthracene to dianthracene. In practice, the investigator uses a calibration curve to convert decrease of anthracene in solution to solar radiation received. Our results show that significant errors occur when a calibration curve is used under different atmospheric conditions than those under which it is prepared. The reason is that the ratio of solar UV to other portions of the solar spectrum reaching the earth's surface is modified by atmospheric conditions. Furthermore, percentage of UV in the solar spectrum is modified by latitude, season, time of day, atmospheric pollutants and layers of water and vegetation. Thus, successful use of light meters that utilize chemical conversions by solar UV to measure other portions of the solar spectrum are dependent on the preparation of a calibration curve for each condition under which the meter is used.