1 watt is fine to be seen but not to see with. On the road you need at least 3w and off road 5w.

But it is not only the wattage of the bulb- there is the light pattern aswell. This is why I prefer 2 bulbs and I have a USE Exposure Enduro with twin 5w leds. For road use it is probably over the top but I use it on low power on most road riding. However- offroad and fast speed has taught me you can only ride within the limits of the lamp.

Look a bit further and you may be able to find some of the "Old" Halogen lamps that have up to 10w bulbs. Old hat now with modern technology so they are going cheap but a Halogen bulb gives a good clear light that is easier to see by. But the 5 or 3w rule still applies.