Commercially Available Phototherapy Devices for Treatment of Depression: Physical Characteristics of Emitted Light

The purpose of this study was to evaluate key physical properties of commercially available light devices for the treatment of seasonal or nonseasonal depression and to determine whether the devices met clinical criteria, derived from evidence-based clinical guidelines, for generating adequate light at a reasonable distance, over a reasonable field of illumination, and with an adequate degree of user acceptability.

Twelve manufacturers loaned or donated 24 light therapy devices: 16 light boxes, one light column, four light-emitting diode beam devices, and three light visors. Each device was evaluated for spectral power distribution, light dispersion, subjective discomfort from glare, adequacy of diffusion, photopic illuminance (in lumens per square meter [lux]), melanopic illuminance relative to photopic illuminance (efficacy ratio), and blue light hazard relative to melanopic illuminance (protection ratio).

Physical properties of emitted light varied widely among devices. Only seven larger light boxes satisfied the three clinical criteria. Some devices advertised as "10,000-lux" devices produced this intensity only at unreasonably close distances, over a restricted field, or with unacceptable glare or unevenness of illumination. Five other devices emitted light with physical properties whose efficacy is less supported by research, although these devices may be useful for some patients.

These results should help clinicians identify appropriate devices for patients seeking light therapy for seasonal or nonseasonal depression. Device selection is key to ensuring that patients receive evidence-supported doses of light.