In LDS doctrine, what is the difference between the Holy Ghost and the Light of Christ?

The Holy Ghost is usually described as the member of the Godhead that helps us know what is true, prompts us to do good, and generally helps us feel God's influence. I've often heard it described as something similar to a "conscience" that helps us know what is right and what is wrong. I've heard very similar descriptions for the Light of Christ. Both are available in some degree to everyone, and both are experienced less when we go against God's will. So what's the difference between the two, or are they the same thing?