Photo Editing: Adobe Light Room or Photoshop?

I have been a photography enthusiast for years and am now creating my own photography business. I have a good idea on all of the equipment I need except for one thing… the photo editing software.

The two programs I am looking at right now are Adobe Lightroom and Adobe Photoshop. I am a complete novice and haven’t even looked at either. I’ve only used iPhoto, Picasa, and Picnik, but I need to upgrade to a professional level software if I want to be successful.

My question to you: Which program (or something better that I haven’t listed) is good for a photographer just stepping out into the professional world? I would mainly be doing senior photos, weddings, and other events for my business, but also landscapes and other types of photography for personal use.

I would appreciate any feedback!