Try going to a Graingers industrial supply store or struggle through their web site and locate any of the following GE PAR36 bulbs: 4509, 4700, 4519, and Q4509 at around $19.00. While they all claim 100 watts at 13 volts they tend to list short life-spans indicating they are already over-volted. 12 volts would be fine. They go from spot to very narrow spot beams. If you are worried about speed get the Q4509, an aircraft landing light. I have used one of these lights in a standard rubber tractor headlight mount for $8.00. $50 for a heavy SLA of adequate capacity. I have been on a lot of night rides with many others and nothing, but nothing, compared with mine for sheer power. Fill the whole road out to 2 blocks and reflective signs show up 1/4 mile away. Total cost $100 or so.