I have been using a cateye bike light with orange sweet paper as a filter, powered by a 6v battery tucked under my left armpit. However I recently visited a Tesco Extra store and found what I think is a bargain. A black C cell torch costing £12. Puts a light out over 70 yds and for me is perfect. The torch is 30mm so mounting it to a sight bracket wasn't too difficult.
£12 and a couple of rechargeable batteries compared to £60 + was no contest