In response to enquiries: the rubrics of the Roman Missal (pre-conciliar) require the lighting of the Sanctus candle, so-called because it is lit by the server at the start of the Canon, a candle on the Epistle side of the altar, originally intended to help the celebrant better see the missal and the elements he is to consecrate and handle. It remains lit until after Communion, being extinguished after the purification of the chalice.
Whatever of the rubrics, however, the use of this candle had so far fallen into desuetude that the contrary custom – that is, not to light it – came to have the force of law! In some congregations and in some places, the custom was maintained: as mentioned earlier, the Dominicans at least in some areas still use this candle (I can recall lighting this candle when serving Fr Christopher's private Mass), and similarly some of the Australian Latin Mass centres have this as an "immemorial" custom (meaning, let us be candid, that they can't remember when they started doing it, since I greatly doubt that the old Irish priests who said the holy Mass in Australia had brought this nicety with them from the Emerald Isle).
As the old Catholic Encyclopedia put it in its article on Candles,
The rubrics of the "Roman Missal" direct that at the Sanctus, even of any private Mass, an additional candle should be lighted and should burn until after the Communion of the priest. This rubric however is much neglected in practice even in Rome itself.