Black being at the dark end of the colour spectrum definitely underplays the amount of light it diffuses. However, that is usually controlled with the amount of wattage that you make choose for your lamp. Moreover, with lamp shades usually being open on both the top and bottom, light freely comes through the open ends while the shade portion keeps it controlled based on the wattage amount. So in short, it keeps it as dark you want your room to be depending how much wattage of bulb you use.