I'm currently running two of these and I am going to take them along on my shakedown tour in a couple of weeks. From my observation currently, the brightness of the bulb appears to be related to the amount of charge. On very sunny days they will be bright indeed. I'm now experimenting with where to put them on my bike for maximum recharging.

The one in my hammock is quite bright enough for reading as it is about a half metre from my head. As for using it outside at night, I've also experimented with that but I'll have to get back to you after the shakedown, as there is too much light pollution from other sources here in the city.