I have a Planet Bike 2 W headlight (nothing special) and when running in flashing mode have had oncoming cars flash me with their highbeams while the sun was setting. Clearly, they thought it was too bright. The other day, I was traveling fast down hill and this really bright light caught my attention. I couldn't make anyting out but after a bit it flashed again. As I passed, I finally saw it was an oncoming recumbent. The slow flash rate had made it difficult for me to identify the source. I guess the lesson here is that there are intensities and flash rates that, depending on conditions, are optimum to achieve the desired effect.