Scientists first started measuring things like light in the seventeenth and eighteenth centuries. They have used numerous methods of classifying light sources. An early method was to use the unit of candle-power whereby a light source was said to be equivalent to a given number of candles. (Over time, this unit became first the candela and then the lux or lumen, terms which were far more precise but not so readily accessible to non-technical people.) This unit of measurement is still quoted today because it is simple to understand. It is, however, not very scientific and therefore not very precise. Light sources today are frequently given by non-scientists as 100,000 candle power and we often read that the brightest lights ever used in lighthouses were a few millions of candle power.