How much light is enough for year round commuting? I used a Cateye Single Shot for 5 years until it died. Now I use a Cateye Single Shot Plus that I picked up on Ebay for $50. It's noticeably brighter than the Single Shot, but with my new commute I'm finding I need something much brighter. Dead animals, collision debris, Mother Nature's debris, a faster road, and long stretches that aren't illuminated.

I've searching in vain to find any sort of lumen estimation of the Cateye Single Shot Plus, and I've read a number of critiques of the various candlepower to lumen conversions being flawed.

Have my eye on the Light and Motion Urban series--specifically the 800 Fast Charge. 800 lumens for $180 seems a good lumen/dollar ratio, and $180 is about my spending comfort limit. Put the Urban on my handlebar and move the Single Shot Plus to my helmet.

If money were no object, I'd get a pair of 2000 lumen L&amp;M Secas--one for my handlebar and one for my helmet. However, I don't think I could successfully pitch $1,000 worth of bike lights to the wife.

Does this seem like overkill?
Going fast on unlit roads you definitely want a decent light. Personally I find the combination of my 100 lumen dyno headlight plus another 100 lumens on the handlebars to be enough, but I ride relatively slowly and on a manoeuvrable bike. On a faster bike with handling and brakes designed for speed you want more. Perhaps not 2000 lumens - that's off road singletrack territory. And price. If you get a better quality 200-300 lumen light that actually puts out 200 lumens you'll be much better off than with an off-brand "500 lumens" that is actually 200...

One consideration is how people coming towards you. While it's annoying to hit a small, dark-coloured lump and end up on the road, it's worse to blind an oncoming motorist and end up as a hood ornament. It's not as bad on bike paths, you're more likely just to get beaten up if you blind someone. Paying a little attention to how much light, and where you're pointing it, is important. With a high powered helmet light it's really important not to look at people's faces... when normally you should be looking there. My preference is to have a relatively low-powered helmet light for that reason - I can still look at faces, and people will see me but not be blinded unless they're already very close.

Nathan's Bike Light Database is a good place to start.