Wattage is the measure of electricity consumed. Some types of lighting systems are more efficient than others i.e. they produce more light and less heat per watt consumed. Different types of plants require different light levels. Salad greens and culinary herbs require less than vegetables and tomatoes that must flower to produce their fruit. If the crop you choose to grow prefers hot sunlight in its natural environment, then you have to give it a lot of artificial light to produce satisfactory results.
Colour spectrum is another important factor.
Types of lighting Many of the various lights on the market are not suitable for high yield rooms. They are inefficient, not bright enough and have an incorrect colour spectrum. Self-ballasted mercury or low pressure sodium lights are not appropriate as the main lighting source for a high yield crop. They are only suitable for cuttings, houseplants and seedlings. Fluorescent tubes tend to come in standard lengths and must be used in special fixtures.