Major depression with a fall/winter seasonal pattern, also known as seasonal affective disorder (SAD), is a recurrent and prevalent disorder. Treatment may include either pharmacological (antidepressant) or non-pharmacological options, most commonly light therapy. Over the years, light therapy has been explored using various delivery methods including light-emitting diode (LED) devices. For over 20 years, cool-white fluorescent sources that yield 10,000 lux of polychromatic white light have been the standard treatment for SAD. Many investigations have confirmed the clinical effectiveness of white light, its overall tolerability, and adverse reactions, such as agitation, insomnia, and headache. Building upon this, more recent studies have compared alternative light sources and different wavelengths of light, such as white, red, green, and blue. If certain wavelengths are more potent and effective, lower intensities of light could reduce side effects and increase tolerability and adherence. Furthermore, studies of the ocular system particularly, intrinsically photosensitive retinal ganglion cells, discovered differences among specific wavelengths of light. While some reports have suggested that 446–477 nm wavelengths of blue light may be the most potent, published clinical trials have revealed mixed results. The purpose of this session is to review the state of the science on light therapy in the treatment of SAD, and suggest recommendations for clinical practice and implications for patients.