Dear Rich: About 10 years ago, I developed a concrete landscaping paver that was poured with fiber optic cables embedded into the paver itself. The fiber optic cable is then joined up with a light source, which illuminates the top side of the paver, offering a unique night time accent lighting. Everyone who sees them in my garden loves the idea, and has suggested that I make an attempt at selling them. Here I am almost a decade later, and I have finally gotten the urge to make a go at it. After a little research, I found that an existing company is selling a patented product that is almost identical to my own. Despite being very similar, my product has a distinct difference, in that the light source in my design is removable from the paver body. I would like to know if this subtle difference is sufficient enough to proceed forward, or if there are too many similarities, thus constituting patent infringement? If your invention has or performs all of the elements contained in the main or broadest claims of the existing patent then most likely you have infringed the patent. Even if your invention has additional elements, it will still infringe. For example, if the patent claim recites three elements, A, B, and C, and your invention has these three elements, it will infringe. Even if your invention has four elements, A, B, C, and D, it will still infringe. Beyond that, the Dear Rich staff is unable to give you more specific information and -- as much as we'd like to save you money -- you'll probably have to pay a patent attorney for a more specific opinion. That investment of a few hundred dollars will be worth it if it saves you from litigation or having to shut down a business in which you've invested your IRA and 401K. Judging infringement. We asked Patent it Yourself author David Pressman about your situation. He suggests that in order to analyze infringement, you should make a claim chart with two columns. Break the first independent claim into its elements, each one in a respective block in the left column. In each corresponding block in the right column write a brief narrative stating why you feel the corresponding element in the left column is met (or unmet) by your device. If the other independent claims differ substantially from Claim 1, you should definitely do them. And keep in mind that even if the claims don't literally read (that is, they're not identical), there are still two ways that the patent holder can chase after you: the "doctrine of equivalents" and the "doctrine of contributory infringement." You can learn more about patent infringement, here. Some other stuff to consider. Obviously, it's too late for you to get a patent. You say you developed your innovation 10 years ago. That's about the same time as the patent in question was filed. If you published information about your invention either more than one year prior to the filing of the patent (or any time before the patent holder's date of invention), you might be able to argue that the patent should not have been issued because it was not novel in light of the prior art. We're not recommending that as obviously, that can be an expensive and time-consuming battle. Which leads us back to our caveat -- if you're seriously thinking about moving ahead with your innovation, consult a patent attorney.