Martin Lowenthal, a psychotherapist, meditation teacher and student of Tibetan Buddhism, has been doing dark retreats for 14 years, a practice he describes in his book Dawning of Clear Light: A Western Approach to Tibetan Dark Retreat Meditation.

How does going into the darkness illuminate things?

Our visual capacities in everyday life are bombarded by lots of external images. Often, there isn’t much room for other images to arise, other than in our imaginations. The idea of the dark retreat is not only you create a setting in which you have no visual stimuli, but you also sufficiently relax your body and your mind so that the deeper aspects of your core awareness can arise. That’s when these truths, along with lights and visions, can become evident.

Over the centuries, people have done these retreats in caves and in the basements of temples. Where do they do them now?

I learned the tradition from Tibetans, who have rooms built in monasteries for this purpose. When I first started doing retreats, I converted a room in my house by blocking off the windows with materials used in photographic darkrooms.

How long does a dark retreat usually last?

That depends on the person. Tibetans often do it for 49 days. And there are stories of yogis who stay in for years. When I first started, I just did three days and I’ve worked up from there. The longest I’ve done is a month, but I tend to do at least two weeks a year. — Beliefnet.com