Can an installer use the Christmas lights I already own?

Some will. We install customer-owned lights and it's usually the cheapest option since it's labor only. The catch is they have to match our quality of commercial-grade lighting, and many times they don't. The warm whites vary in color and we won't come fix anything for free. So if you want truly hassle-free, just buy or lease the Christmas lights from the outfit you choose. Other installers lease their own lights and some require you to buy through them, so ask up front.