A reader asks:

What happens if you use light too early? Once in a while? Regularly?


Light Exposure & Circadian Clock Resetting

A primary effect of light exposure throughout the night and early morning is to reset the internal circadian clock. The aim of light therapy for depression is to reset the clock earlier in order to counteract dark morning bedroom conditions (especially in winter). When light is presented during most of the night, the clock resets later, not earlier. About two hours before wake-up — this is just an average; the timing might differ — body temperature reaches its nightly minimum and the pineal gland stops secreting melatonin. Thereafter, light presentation resets the clock earlier, which is what we want. The switchover from later to earlier clock resetting can happen quite quickly, so we try to avoid premature light exposure, which would work opposite to the desired effect by resetting the clock later.

Early Light Exposure Can Bee Disruptive

Such early exposure even on a single day can be disruptive, and induce a jet-lag-type effect. That is why it makes most sense to skip light treatment on the occasional day you have to be out of the house very early. If you were to use the light too early every day — as your question asks — there are two possible outcomes, depending on whether you happen to “hit” the circadian clock in its delaying or advancing state. On the one hand, you might find it difficult to stay awake, or to become alert till hours later. On the other hand, you might start waking up far earlier than desired. We want to avoid either of those outcomes.