The earth operates on a 24 hour cycle, and so do humans. For most of history, we didn't have much choice in the matter. However, in the absence of visual cues light sunlight, some research indicates that humans naturally stick to a 25 hour schedule. So why rely on the earth's rotation to order our lives?
I-Weather is a website and app that cycles through blue and orange light for a period of 25 hours, 40 minutes and 7 seconds. The blue 'day' suppresses the hormone melatonin and promotes wakefulness. The orange 'night' has no impact on melatonin or other hormones, allowing users to work or to drift off as they please. I-Weather acts like an online sun,"creating the world’s first artificial climate to satisfy the metabolic and physiological requirements of a human being in an environment partially or completely removed from earthly influences." It's good for travelers, insomniacs, and anyone with a grudge against sunlight.
For a more practical way to regulate your circadian rhythms, check out F.lux.