Perhaps the leading Frequently Asked Question for digital photographers. But Lightroom and Photoshop are not equivalent. In fact, they do a lot of similar things, and have passionate admirers among photographers, but they are quite different. We should probably picture two different paths leading to the same destination, each having its own unique set of pitfalls and advantages.
Digital images have opened exceptional creative potential for photographers of all levels. In spite of their differences, both Photoshop and Lightroom are remarkable editing tools. If the one you are using now has never limited your creativity or caused inconvenience, you should probably stay with what you know best. After all, ease of use and an acquired knowledge base are great reasons to choose software for any purpose.
Both Photoshop and Lightroom are highly capable at editing JPEG, TIFF, PNG, or IMG files. Both use the same imaging engine: Adobe Camera Raw. Both can crop, manipulate and tweak images to your heart's content.
Photoshop works like many applications: you open a file, you make edits, and you save the edited file to include whatever changes you judge appropriate, much like a Word or Excel file. If you want many versions of a same image, for example color and black & white, a small file for posting on line vs. a larger one for printing an enlargement, or sometimes a picture of all your cousins plus a cropped version showing only uncle Jim, you'll have to save copies, while protecting the original. And you'll need to manage files and folders to keep track of all your images.
Additionally, Photoshop always works by opening original files. They have become quite hefty with the appearance of 24, 36 and 40 megapixel sensors, and require a fairly powerful computer.
For example, if you'd like 10 photos to have a black & white version, you'll need to save 20 files: 10 originals and 10 black & whites.
Lightroom, on the other hand, is a parametric editor. This means it never changes the original file but it does store whatever changes (or parameters) you choose. In the former example, if you'd like 10 photos to have a black & white version, Lightroom will need only 12 files: the original 10 images plus two files for storing its parameters.
Of course 12 or 20 files is not going to make much of a difference, but, as you know, files add up quickly. Think of the difference between 25002 files and 50 000! Lightroom is also lightning-quick when it comes to sorting, tagging and making basic edits to photos and, if used properly, offers efficient and redundant file sorting and backups.
The devil is in the details, and also in the 2, 3 or 5 percent of images that absolutely need the exceptional power of Photoshop to become reality. Make no mistake: Photoshop is unequalled as a comprehensive and powerful photo editing tool. A lot more than Lightroom.
Photoshop offers more precise masks and contours, an infinite number of layers and ton of filters. The downside of all this power is that Photoshop is more difficult to tame, begs for a powerful computer, creates gigantic files and requires a lot of care in setting up files and folders to store and retrieve your images. Fortunately, it's easy today to use both, with Lightroom allowing users to open images in Photoshop and still use its powerful database features.
So in fact, both pieces of software complete each other very well. If you're starting to get serious about photography, Lightroom is faster, easier, and will allow you to post produce most of your photos to a high level of quality. And because Lightroom is open to working in Photoshop, it allows you to do more complicated stuff when the need arises. So if you're getting started, the answer is not Lightroom or Photoshop. It’s Lightroom and Photoshop.
If, however, you know Photoshop very well and you have a great filing arrangement, you might not see any advantage in moving to Lightroom, and you might be right... that is until you get a taste of correcting white balance for a whole afternoon's shoot with one click.