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This is hard as there are many times in which any site would want to rank for a related keyword, but the search engines are only interested in showing content that the searchers want. So if someone is searching for light show, they are probably looking for a light show. If you had a page that had videos of light shows using your product (the videos have to be yours) and maybe upcoming light shows using your lights, that would make sense. You could even have a section of your site dedicated to promoting light shows in different parts of the world or country. It could be a light show guide, ultimate resource. That might rank for it, but just your homepage isn't going to be a good result as it probably doesn't answer the query for "light show". Stop thinking about how to optimize and start thinking about how to answer people's query. If your site or page isn't the best answer, it's not something you should be worrying about. If you can be the best result, then make your site/page the best result with content. No amount of onpage optimization will help you rank for related terms unless you can answer the query at hand. Hope that helps!