They are also high in red wavelengths, but deficient in blue. Plants absorb light of many wavelengths, but mostly in the blue and red range. They absorb little in the green range, which is why leaves look green to us. To get an idea of wavelengths, just look closely at the colors of a rainbow. You can see red and orange on one end and blue and violet on the other end.
Light also includes infrared and ultra violet light on the far ends of the rainbow.
Intensity is traditionally measured in footcandles, which is the amount of light an international candle casts over a one square foot surface area from one foot away. To approximate 100 footcandles, hold your hand one foot away from a white piece of paper. If you can see the shadow of your fingers, then the light is at least 100 footcandles. Because electric lights don't have the intensity of the sun, we generally leave the lights on longer to compensate. However, plants do need some dark time.