"S"- standard mode. It runs at full brightness, which we recommend for the summer months when the light is fully capable of recharging during the day.
"P"- power-saving mode. This runs the light at 50% capacity/brightness, which extends the runtime of the light during winter months when rechargeability is affected by the availability of UV rays.
Sadly you can't. We are looking into labeling them in the future. The only way to tell is by using them and if the 300 run out faster than the 100 and try swapping them around.