You're going to have a hard time finding LEDs that can put out more light than a 21 watt incandescent bulb. I have some slightly brighter regular bulbs in my car. They look like an 1156, but are maybe 15-20% brighter. They don't last very long, though. I'll have to look this weekend and see what the number is. They also make halogen bulbs that fit an 1156 socket, but they run so hot that there's a risk that you'd burn the plastic lenses.