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.

Answer 2

Well, explaining circadian rhythms and bright light therapy to a 5-year-old can be a bit challenging, but let me try my best!
You know how our bodies have an internal clock that helps us know when to sleep and when to wake up? It’s like a little timer inside us. This internal clock is called the circadian rhythm.
Now, sometimes our internal clock can get a little confused, especially when it’s dark outside, like in the morning during winter. It thinks it’s still time to sleep, but we need to wake up and be active. That’s where bright light therapy comes in!
Bright light therapy is a special kind of light that’s very, very bright. It’s like sunlight, but even brighter! People use this bright light therapy to help their internal clocks get back on track. They sit in front of a special light box that gives off this bright light.
Usually, our internal clocks get reset with just a little bit of light, like 400 lux. But for bright light therapy, they use a lot more light, like 10,000 lux! It’s super bright! And they do this for a longer time, like 30 minutes, to make sure it really helps.
By getting this super bright light in the morning, it tells our internal clock, “Hey, wake up! It’s time to be active and energized!” It helps our bodies know when it’s daytime and when it’s nighttime.
So, in simple words, bright light therapy uses really, really bright light for a longer time to help our internal clocks know when to be awake and when to be sleepy. It’s like giving our bodies a big wake-up call!