Sunlight is good for human health. And even the small percentage of it that’s ultraviolet is good, because it makes our skin generate vitamin D. But as you know, too much UV can give you a burn. And too many burns can spell skin cancer down the road. Right now, the sun’s UV is at its strongest of the year. About 1 percent of the light hitting a sunbather is UV, which translates into a million trillion photons per second. All are capable of altering DNA and epidemiologists have found that every 1 percent increase in lifetime UV exposure produces a 1 percent hike in skin cancer incidence. Obviously the bottom line is: avoid most of it.