You do understand what lux is a measurement of, don't you? If a source of light spreads the available lumens over a greater area, the lux is lower and the ability to 'blind' someone is greatly reduced. The light may have a lot of glare but hardly 'blinding'. If the beam is tight and the lux is high, the ability is 'blind' a driver is also reduced because it's tightly constrained and has much less glare, although it would be brighter if seen from directly ahead. Since we don't tend to ride over where the drivers are, a tight beam isn't going to be a problem either.