What I see is the fact that 'yes' you can make a light work using the white wire. However, when I think of lighting for a bike I want to 'see' as well as 'being seen'. 3 watts from an incandescent lamp or what limited lighting you'll get from small LEDs isn't going to provide you with enough light to see anything ahead of you. If you're gong to ride at night I'd think you'd want to see where you're going, as well as providing enough illumination to be seen by others.
Think of it this way; when you ride during daylight hours how many times have you had to avoid something in the road ahead of you? A rock, a stick, a pothole? And how far ahead of you did you see that potential hazard? 50 feet? 100 feet? Now think about riding at night with limited forward visibility. Like I said, I want to see what's out there, before it's too late.
Tom