Formal Aspects of Light Therapy

Formal Aspects of Light Therapy

As noted earlier in this chapter, light therapy appears to be mediated via the eyes rather than the skin. It is important for clinicians to inform patients of this observation, as many patients will otherwise not appreciate the importance of ensuring that their eyes are open during treatment sessions and are at the appropriate distance from the light source. In addition, it is important to emphasize that there is no evidence that tanning salons, where the eyes are generally covered and the subject's skin is exposed to light, are useful for SAD. In addition, the light sources in tanning salons are by definition high in UV rays, which can be harmful to both the eyes and the skin. Because UV light is not necessary for an antidepressant effect (Lam et al. 1991; Oren et al. 1991), use of light devices that emit UV light is contraindicated.

Although the initial light treatment studies were performed with full-spectrum lights (i.e., lights that mimic in their wavelength range the spectrum of sunlight), more recent studies have shown ordinary fluorescent lights to have significant antidepressant effects (Oren and Rosenthal 1992; Rosenthal 1993). In addition, there is no evidence that full-spectrum light is superior to ordinary fluorescent light (Lam et al. 1992). Patients often ask whether it would be helpful for them to replace all the fluorescent lights in their home or workplace with full-spectrum lights, indicating a lack of understanding that it is the intensity of light rather than its spectrum that appears to be of critical importance in achieving an antidepressant effect.

Light Therapy Introduction Diagnostic Indications and Contraindications

• Indications
• Contraindications to Light Therapy Evidence for Efficacy
• Acute-Phase Treatment
• Maintenance/Continuation Therapy Formal Aspects of Light Therapy Novel Treatment Devices Practical Aspects of Light Therapy Conclusions

Initially, white light of 2,500-lux intensity was tested as the active treatment modality against light sources of lower intensity (Oren and Rosenthal 1992; M. Terman and Terman 1992) and was found to be superior. The 2,500-lux intensity was chosen because it had previously been found to be capable of suppressing nocturnal melatonin secretion (Lewy et al. 1980). The original 2,500-lux light boxes were placed vertically on a table or work surface 3 feet away from the user's eyes. Currently sold light boxes are slanted toward the user's face in such a way as to bring 10,000 lux to the eyes. The chief advantage of the new boxes is that antidepressant effects can be obtained from shorter treatment sessions (e.g., 30 minutes rather than 2 hours) in some patients (J. S. Terman et al. 1990), suggesting a reciprocal relationship between duration and intensity of effective light treatment.