If typical circadian rhythms are entrained with 400 lux of light a few minutes each morning, why is bright light therapy (BLT) set to a standard of 10,000 lux for 30 minutes each morning?

Question

And: would BLT at 10,000 lux at 5 min/day eventually have the same effect as morning sun exposure?

Thank you!!

In: 5

Answer 1

The circadian rhythm isn’t only set by the light of dawn at 400 lux. It’s set by the much brighter morning sunlight once the Sun is a bit above the horizon, which happens pretty quickly, pushing illumination up into the thousands (and the difference is even stronger for blue light, which is what’s relevant for circadian rhythms; blue light is mostly scattered or absorbed away at dawn).

That said: the point of bright light therapy is specifically to nuke your circadian rhythms because they *aren’t* responding to normal signals. If you had normal circadian rhythm responses, you wouldn’t be using the therapy in the first place.