The jar is properly known as a carboy, from the Persian word qaraba (large jug or flagon). It was actually fairly small when it first took its place in pharmacists' windows in the seventeenth century. The liquid-filled vessel was useful in distinguishing the pharmacist from the apothecary who displayed a pestle and mortar.
As shop windows got bigger, so did the carboys, so the Victorian version was pretty large. Originally the carboys contained medicinal liquids but by the twentieth century their function became symbolic and they were filled with brightly-coloured liquids.
Even the use of lighting in this modern version is not anachronistic. Carboys began to be lit up in the nineteenth century, when chemists would use gas burners to light them from behind.