Figure 1.

(A) The measured irradiation spectra of the Ultra-Vitalux lamps (solid) and the average solar irradiation spectrum as reported by Chu and Liu (2009) (dashed), scaled to a global radiation of 1000 Wm⁻² at 300–4000 nm, approximating the global radiation (i.e., including both direct and scattered or reflected radiation) in Finland at noon on a cloudless summer day. (B) The alternative spectral weighing functions used to estimate the biologically effective radiation dose in the treatments shown standardized to 1 at 300 nm. Gray: Quaite et al. (1992) as formulated by Musil (1995). Black, solid: Flint and Caldwell (2003). Black, dashed: the energy content per photon relative to the energy content of a 300 nm photon.