A reader asks:

For a long time now I have realized that I am not able to remain active at all without natural light. As long as I am outside, my energy level is great; however, as soon as I enter my house, my energy level is down by 80%. I have to push myself just to take care of daily chores. For years, I have known that some people need daylight just to function. I am not quite that bad; however, I do think I need daylight. Do I need light just in the evening hours when I am inside? Or do I need the morning and night light?

Answer:

This is a clever and poignant question. It is possible that what you lack specifically is adequate early-morning light exposure, close to the time specified by CET’s Automated Morningness-Eveningness Questionnaire. Such light readjusts the internal biological clock which controls energy cycles. If that is the answer, light later in the day would be a secondary factor, possibly even irrelevant. However, bright light exposure can also exert a direct energizing effect, no matter what time of day (or night) it is received. “Better than coffee,” as one patient called it. If that is the answer, you might benefit by installing a light therapy apparatus at your desk at work, turning up the level whenever you start to slump. See CET’s recommended DaylightXL, at cet.org/cet-online-store/, which was designed primarily for that purpose.