Leonardo da Vinci, one of the greatest creative thinkers of all time, strongly recommended the habit of meditation in the dark. He wrote: "For I have found in my own experience that it is of no small benefit, when you lie in bed in the dark, to recall in imagination, one after another, the outlines of the form you have been studying." He often awoke to find his problems solved. Da Vinci would often stand silent and motionless before a painting for hours, without using his brush, as though waiting for spiritual guidance.