A reader asks:

Have any studies been conducted in a clinical setting on the possibility of adverse effects on the retina with any light source of 10,000 lux?


The largest study, for 10,000 lux, 30 min daily exposures for up to six winters, was reported in the American Journal of Ophthalmology (for a download, go to www.cet.org/resources). No ocular abnormalities occurred. The authors concluded that light therapy “appears safe for the eyes. Current knowledge is insufficient to specify any definite ocular contra-indications for bright light therapy, although we recommend that patients with preexisting ocular abnormalities and those using photosensitizing drugs undergo treatment only with periodic ophthalmologic examination.” Although there are no definite coutra-indications, we also recommend that alternatives to light therapy be used by patients with retinal degenerative disease