You can easily surpass the light intensity of direct sunlight with grow lights. Outdoor sunlight average is 50,000 lux, which is 50,000 lumens per square meter, or around 4700 lumens per square foot. My 400 watt HPS (Hortilux) bulb puts out more light than that. If you restrict a 1k light with a good bulb to, say, a 4'x4' area, you get around 8000 or so lumens per square foot, nearly double that which outdoor sunlight would provide. Obviously distance-from-light plays a role with grow lights, but if you keep plants relatively close to the lights it is not at all difficult to surpass direct sunlight with grow lights.