Light travels in a straight line. Draw a diagram with you on a bike on the side of a road approximately 15 feet from the centerline and about 20 feet from the driver of oncoming car. Draw straight lines for the light from your lights and from the car's lights (car 1). Put in an oncoming car whose driver's side headlamp is only 3 feet from car number 1. Which light is going to be blinding the oncoming driver?

Bonus points: Draw lines from your lamp (and the car's lamp) indicating the beam spread for both vehicles... say from 12 degrees up to 35 degrees. The lines will indicate that some of your light will reach the car but some of their light will reach you. Add in car #2 and see where their lights go.

But now consider how many lumens your light (and the cars) puts out. Those lumens can be expressed as lux or lumens/sq meter based on the area of the target. That target is the base of the cone of light from your lamp. The further away the target, the lower the lux of any light. Your light, 15 feet from the center line and 20 feet from the driver is going to have a very low lux by the time it reaches the driver. The light from car #2 has a much higher lux.

Bottom line, don't worry about blinding oncoming traffic. Chances are they aren't even going to see you. If your lights are too polite, i.e. too low power, the chances of not being seen are even higher.