Incandescent lightbulbs are the traditional light bulbs. These bulbs pass electricity through a conducting filament inside a vacuum to create light. They have been existence since they were created by Humphry Davy in 1802 (a little outdated?). Of the three types I will talk about this is the cheapest lightbulb coming in at between $.50 and $1.00. They have very short lifespans of about 1,500 to 3,000 hours. These lightbulbs are also very inneficient as they only convert between 10 and 20% of their energy to light. The rest of the light is converted into heat and essentially wasted. This is why easy-bake ovens use incandescent lightbulbs to cook; if they create mainly heat they are much better at cooking than creating light. The only benefit to these bulbs besides being cheap is that they have a "preferable" color of light to some people.
Over the past few years the most popular new lightbulb has been the CFL or Compact Flourescent lightbulb. This type of bulb excites mercury gases inside its swirls which then emmit UV light. This light is absorbed by the phosphor coating on the outside of the bulb, which converts the UV light to light in the visible spectrum. Although they are very popular they have been surrounded with some controversy due to the presence of mercury inside the bulbs. Mercury is a poison. If the bulb shatters this poison can get into the user's house. If your only concern is the fact that this mercury could get into the environment when you throw it out: 1. you should always dispose of these bulbs at certified recycling centers and 2. The amount of mercury that is used in the lightbulb is substantially less than the mercury that would have been emitted by coal-fired plants (which provide the majority of the US's energy) had you used an innefficient incandescent bulb. However recently there has been an addition to some bulbs that prevents this occureence. CFLs can be bought with a silicon coating on the ouside of the bulb. This way, if the bulb shatters all of the mercury can be contained. These bulbs cost about $2 and offer a lifetime of 10,000 hours. Drawbacks are that these bulbs have a warmup period in which they emmit small amounts of light. Also the color is not seen to be favorable or warm. 
The last and most modern type of lightbulb is the LED or light emitting diode. It is the most complicated of these three light sources. In simple terms it puts a flow of electrons through a gas which causes the gas to release photons or light. The color or wavelength of the light can be controlled by changing the gas which in this case is known as the semiconductor material. This is the also the most expensive to buy, with current lightbulbs around $30. As these bulbs become more mainstream though they will become cheaper as mass production takes over. These bulbs are extremely long lasting at around 60,000 hours. They are also the most effecient of any of these options. Some complaints of users have been that the bulbs have a very direct stream of light.
