The 3-watt bulb is used in your B&M light if you do not have a generator powered tail light. The standard bulb is 2.4 watt and is not as bright, but can be used with a tail light. We also carry spare tail light bulbs. 3WB$5.00Type,: 3-watt,2.4-wattTaillight All images and text copyright Velo Orange, LLC 2006, 2007, 2008.