A reader asks:

 In the answer to question #1498 you wrote, “This is the time interval during which you can most easily reset your clock earlier, and such resetting is integral to the antidepressant effect.” If I am using light therapy to combat depression, and doing so resets my clock earlier — but for maximum effect I need to catch the end of my sleep cycle — does this mean I will gradually need to be doing my light earlier and earlier in the morning . . . sort of chasing the clock backwards, if you will?


Thankfully not! The recommended time is relative to your sleep interval before starting treatment. Once the initial adjustment is made, one can ordinarily keep the session time constant while maintaining the benefit. If you were to “chase the clock,” you would find yourself in the bizarre position of sleeping during the day and being awake at night — indeed, that is a strategy useful to night-shift workers in critical care occupations. But it is probably not for you!