Without enough light a plant will die because it's unable to perform photosynthesis (convert food into energy). The good news for hydroponic growers is that plants are able to make use of artificial light to perform photosynthesis, as long as there is enough light.
High Intensity Discharge (or HID) Grow Lights - are the most efficient source of indoor lighting available to hydroponic growers. HID lights are the most comparable to sunlight. They emit 4 to 6 times more wattage and will last longer then all other types of hydroponic grow lights. HID bulbs range in wattage from 100 to 1500. The only disadvantage of HID lighting systems is that they produce intense heat, which can dry out plants and even start a fire if not monitored carefully.
There are two types of HID lights - metal halides and high pressure sodium lights - each type of HID bulb emits light from one side of the visual light spectrum for different effects on plants. The visible light spectrum ranges in color from red (at one extreme), orange, and yellow, green and blue-indigo (at the other extreme).
Metal Halide Lights - immerse plants in light from the blue end of the visual light spectrum. Blue light is an indicator of springtime and it urges the plant to grow. Metal Halide lights are especially good for growing bushy plants such as lettuce, spinach, cabbage and herbs.
High Pressure Sodium (or HPS) Lights - immerse plants in light from the red/orange end of the visual light spectrum. Red mimics the color of the autumn harvest and urges plants to flower and produce fruit. For this reason, high pressure sodium lamps are especially good for growing fruit and flowering plants.
Fluorescent Lights - are most effective to sprout seedlings and to initiate rooting in plants. The average fluorescent bulb only produces 2300 lumens - which isn't enough to grow even small plants. Even the highest-powered fluorescent lights have a minimal growth effect compared to HID lights. However, the benefits of using a florescent bulb include its energy efficiency, its low price and its low heat production.