Double Shotting

This refers to the practice of adding an extra torch ball before the previous one has gone out.

This has the effect of giving more light, but for a shorter period than you'd expect. I'm not sure, but I think it also results in the paraffin evaporating faster, and leaving more of a lump of unburnt cotton behind.

So, very much a judgment call - probably inadvisable too early in the evening, but quite a good idea by the end.