An Elevation Candle, is, as the name suggests, a candle lit at the Elevation of the Host and Chalice. If you have ever been to a High Mass, (occasionally a Sung Mass), two of them are lit. Before 1960, it was directed that one Elevation Candle be lit at the Elevation at Low Mass, but this had largely died out in most places, so the Holy See removed the requirement to use an Elevation Candle at Low Mass. Elevation Candles are still required at High Mass.
The original purpose of the Elevation Candle was so the people could see the Host and Chalice, but because of modern lighting, it now represents the Light of the Lord.
I just don’t know if the Elevation Candle can still be used at Low Mass, and if it can be used in the OF.