You can buy an extremely bright, high quality bike light for less money now than ever before. The changes due to LED lights have been amazing and very beneficial to cyclists. My Light & Motion Urban 800 cost me a little more than $100 new and puts out more light with good battery run time than a light that would have cost more than $500 a few years ago. You can buy equally bright LED flashlights for even less.

I also agree with others that you need a less bright light on dark, unlit roads than in the city with much more ambient light from signs, street lights, cars, etc. It's counter-intuitive, but your eyes adjust to dark conditions and pupils open wider. However, in moderately light conditions such as urban areas, your pupils don't open as wide. You also need brighter lights in the city so that car and truck drivers can see you.