Chromotherapy, also known as color therapy, is a pseudomedicine based on a holistic approach and on a mixture of esoteric and scientific concepts. In a nutshell, it is the use of colored light applied on the skin or eyes to heal various health disorders, assuming some (scientifically undescribed) beneficial effects of color on body and mind. Traditionally, "color therapists" use white light sources to backlight colored filters. Nevertheless, driven by recent progress in solid-state lighting technologies, light-emitting diodes (LEDs) will probably become the most used light sources in chromotherapy. Some LED-based chromotherapy lamps are already available on the market. The main interest in LED lamps--in addition to their energy efficiency and long lifetime--is that they can provide various colors directly depending on the nature of the semiconductor inside without using any filter. Is the use of LEDs in chromotherapy without any risk?
Blue Light Hazard
In the last quarter of the twentieth century, the work of Ham, Mueller, and Sliney (Sliney et al. 1976; Ham and Mueller 1989) opened the way to the description of photochemical mechanisms of lesions on the retina during exposure to a blue light source. To prevent such damages, the International Commission on Non-Ionizing Radiation Protection (ICNIRP), in its "Guidelines on Limits of Exposure to Incoherent Visible and Infrared Radiation" (1989), defines a blue light action spectrum B[lambda].([lambda]) and exposure limits (expressed in radiance) that are used in IEC 62471, which is the standard when dealing with exposure to sources of broad spectrum incoherent optical radiations. The application of this standard is particularly justified for evaluating blue LED and white LED (also called White Phosphor Coated LED, or WPCLED, and made of a blue LED coated with phosphor), which combine high radiance and a blue-enhanced spectrum, as can be seen on Figure 1. In 2010, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) published a collective expert report making an update on the blue light risk associated with the use of commercially available blue and white LEDs (Rapport de l'ANSES 2010). The results showed that it was possible to buy white or blue LEDs lamps reaching the medium risk group (RG2), potentially harmful to the retina of the eye if not diverted in 0.25 seconds.
In Europe, the design standards of lighting fixtures now include photobiological safety requirements based on standard IEC 62471 or its application report IEC TR 62778. Scientific work is still ongoing to better understand mechanisms of blue light-induced damages and to improve prevention (Jaadane et al. 2015; Behar-Cohen et al. 2011), but current exposure limits seem to manage the risk for general...