Solar panels can produce electricity (just a wee bit albeit) even in very low light levels. In fact, I've heard of folks who have said they get a voltage reading across their solar electric panels on their home under bright moonlight. That said, the amount of power being generated at that low lux is of course low.
Solar panel manufacturers rate their modules assuming 1000 watts per square meter of sunlight. This amount is approximately the power sunshine produces on a clear day pointing directly at a solar panel. In terms of lux, this is just a simple conversion:
1 Lux is equal to 0.001496 watts/square meter
668,449 lux = 1000 watts/square meter
Solar panel technologies range from 8-17% efficiency. So that means that say a solar panel that is 15% efficient (in converting direct full sunlight to electricity) and let's say is 1 meter squared in size then it would produce 150 Watts (1000 Watts/square meter x 0.15 efficiency x 1 meter) or 100,267 lux.
Of course if the sun is not shining directly at the solar panel then it'll produce less power - with the extremes being at dusk and dawn usually. Solar panels can actually produce more power than what they are normally rated for in full direct sunlight. This effect can occur when there's reflection of sunlight from nearby water (e.g. a lake or a pond) or snow. The reason for this is of course that more light, more Lux is falling on the surface of the solar panel.