Incandescent are the cheapest grow lights available. There is a good reason for that.
Incandescent systems simply do not produce much in the way of results. They emit a lot of heat and, therefore, have to be placed at a distance from the actual plant growth. This results in a lot of wasted light that is being produced without affecting the growing plants to any significant degree. Incandescent bulbs do not last very long, further reducing the value of the system. A better option is a fluorescent light system. These are relatively cheap grow lights that can be place inches from the plant growth, maximizing the efficiency of the light generated. Fluorescent bulbs are also available that produce light from different ends of the color spectrum, allowing the gardener to grow different kinds of crops. If you are looking for cheap grow lights, fluorescents are a viable option.
Metal halide (MH) systems are not cheap grow lights to purchase. They can cost more than twice the amount of a fluorescent system.
They are, however, very cost effective to use and excellent results can be obtained with these systems. MH lights cost very little to operate per kilowatt. Your electric bill will be much less for the same number of hours of MH light versus incandescent light. Both these systems produce quantities of light that generates exceptional crop yields. Metal halide bulbs will last several times longer than those in an incandescent system, further reducing the cost to run the system.
High pressure sodium (HPS) lights are some of the most expensive light systems to purchase. They also only produce light in the red spectrum.
The red end of the color spectrum is best utilized for flowering or seeding plants. However, HPS lights have a huge upside in that they are extremely cheap to operate and the bulbs can last for up to two years. HPS systems are not cheap grow lights to purchase, but they are, by far, the cheapest system to operate.
To get the best results from your indoor gardening area, you need an efficient, cost effective light system. Cheap grow lights are usually not the most effective grow light system. Consider the purchase price, the cost of replacement parts such as bulbs and ballasts, and the cost to operate the system. Only when you have factored in all of these costs can you really determine the best value for your gardening dollar.