Light therapy lamps ranked by measured lux at 12, 18, and 24 inch distances, not marketing claims. With $/measured-lux.
Questions logged on this protocol
What lux dose do I actually need?
The clinical SAD protocol is 10,000 lux for 30 minutes within an hour of wake (Terman & Terman 2005, CNS Spectrums). For general circadian phase-advancement in non-SAD users, 2,500-10,000 lux for 20-30 minutes produces measurable melatonin shift (Duffy & Wright 2005). The dose is cumulative: 5,000 lux for 60 minutes is roughly equivalent to 10,000 lux for 30 minutes on the linear portion of the dose-response curve.
Why does distance matter so much?
Illuminance falls off roughly with the inverse square of distance. A lamp rated '10,000 lux' is almost always measured at a specific close distance, often 6-8 inches. Double that distance and you get ~2,500 lux. Triple it and you get ~1,100 lux. The lamps we rank highest are the ones that still deliver dose at an ergonomic distance (18-24 inches) where people actually sit.
Is UV output a risk?
Reputable light therapy lamps (Carex, Verilux, Northern Light Technologies, Alaska Northern Lights) filter UV-A and UV-B. Residual emission is below the ACGIH workplace threshold. Tanning beds and Sperti D-lamps are a different product class, where UV is the active ingredient rather than a byproduct, and should not be used as circadian light therapy.
Does color temperature (CCT) matter?
Less than lux does, but it matters. Melanopsin, the non-visual photoreceptor that drives circadian signaling, peaks near 480 nm. Cooler (higher CCT, 5000-6500K) lamps produce more energy in that band per lux. Many lamps now let you switch CCT; keep it at the cool/daylight setting for morning use. Lockley et al. 2003 (J Clin Endocrinol Metab) showed short-wavelength light suppresses melatonin roughly twice as effectively per photon as longer wavelengths.
Can I use it at my desk during work?
Yes, but dose still requires proximity. A lamp across the room at 4 feet delivers under 1,000 lux: ambient bright, not therapeutic. For a desk setup: lamp at arm's length (18-24 inches), slightly above eye level, angled down so the light enters the lower visual field where melanopsin-rich retinal ganglion cells are densest. Run it for the first 30 minutes of your workday.
What about 'sunrise alarm' lamps, are they enough?
Different product, different dose. A Philips SmartSleep sunrise alarm peaks at ~300 lux at pillow distance: useful as a wake signal but well below the circadian phase-shifting threshold. Sunrise alarms handle the wake moment; a 10,000 lux therapy lamp handles the circadian dose in the 30-60 minutes after wake. They complement each other; one does not replace the other.
How long until I feel the effect?
Alertness changes are same-day. Phase-shift of the melatonin rhythm is cumulative over 3-7 days at a consistent dose. For seasonal affective, meta-analyses (Golden et al. 2005, Am J Psychiatry) show significant mood improvement within 1-2 weeks at 10,000 lux / 30 min / morning. If you see no change after 2-3 weeks of consistent use, reassess dose, distance, and timing before changing lamps.
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