Retina-Friendly Phototherapeutic Light Source – Hypothesis, Formula and Device Fabrication

Winter’s lack of sunshine often leads to seasonal affective disorder, and insufficient morning light exposure can likewise provoke insomnia or even precipitate depression. To address these issues, light therapy has been introduced. However, certain light-therapy protocols can cause ocular discomfort; in particular, overexposure to blue-rich white light is known to induce photoretinitis. Consequently, there is an urgent need for approaches that balance retinal safety with therapeutic efficacy. To date, no quantitative studies have tackled this dual requirement. Here, we propose a novel model that, under the constraint of retinal friendliness, maximizes the effectiveness of light therapy. Our model quantifies therapeutic efficacy via melatonin suppression sensitivity (MSS) and sets the retinal permissible exposure limit (MPE) as the upper bound on treatment duration. Under these parameters, a 6.5-hour light therapy session can achieve up to 79% of the maximal effect, requiring an illuminance of 2,240 lx. Alternatively, a 1.5-hour targeted treatment using 1,000 lx of 620 nm orange light yields 59% efficacy. Furthermore, continuous home illumination at 1,700 K for 6.5 hours produces 77% of the maximal therapeutic effect.