Not Worth the Candle

In order to compare the output from the different light sources that became available in the nineteenth century, the measurement of light was codified., One of the reference standards that was selected was the light from a spermaceti candle of a specified composition and size, made in a specified fasion and burning at a precise rate. But the spermaceti used to fabricate the candle is the natural product of non-domesticated animals living in the wild. It therefore ought to be expected to have great variation in its own composition. How did the governing bodies settle on a spermaceti candle, and why did they continue to use it?