Introduction

Most studies of the effects of UV radiation (radiation with wavelength, λ, < 400 nm) on biological and chemical processes include some component that distinguishes how response varies with wavelength. How fine the spectral distinctions are made depends on the hypothesis to be tested. The simplest hypothesis is whether UV has any effects at all, which is tested using a presence/absence experiment. For example, the effects of treatment exposure to UV and visible radiation (400 < λ < 700 nm) is compared to exposure to visible radiation alone. If there is a difference, then a more complex hypothesis can be tested, e.g. ‘Do effects differ between the three arbitrary divisions of the UV waveband: UV-C (λ = 200–280 nm), UV-B (280–320 nm), and UV-A (320–400 nm)?’ Radiation in the UV-C band is emitted by the sun but does not penetrate the earth's atmosphere. The UV-B band is the shortest wavelength UV in solar irradiance incident to the earth's surface, generally having strong biological effects per unit energy. The energy in the UV-B is small compared to the longer wavelength UV-A band, which has generally weaker negative effects per unit energy. This three-part distinction indicates whether solar UV radiation is capable of inducing effects. Other classifications of UV have been used that even further subdivide each band (Moeller, 1994).

At the other end of the spectrum (so to speak) are investigations that seek the finest resolution possible, i.e. a continuous measure of UV effects as a function of wavelength.