Okay. I think I now understand what you're asking. You're asking how one would replace a light bulb (such as a brake light) with an LED cluster. Yes. You can do this, but there are a couple of bridges you have to get over. You need the light produced by the cluster to be as much, if not more that the original bulb. You also want the cluster to run from the same power as the original bulb (preferably less current though). There are newer types of LEDs that are very bright. Enough to do just what you're asking. The problem is that they tend to be very expensive too. Much more than the cost of the bulb it will replace. They actually are more economical in some cases such as Tail Lights and Traffic Control Lights. The reason is because they don't burn out as quickly under normal load. They should last so long as they end up cheaper than the bulbs, cost of replacing them and the power used. Using a cluster of regular red LEDs for a bicycle tail light might be sufficient, but be sure not to over drive them. They likely would not be visible in the daytime, but that's not when they're most needed.