Candle reaches Latin candēla, formed from candēre, to shine or be bright. Old English borrowed the noun as candel, also found in Middle English.
The first step is noun formation from a verb, not just a spelling change. One candel card represents the spelling shared by earlier English stages.
Sources
- Merriam-Webster: candle
Noun Word History gives candēre, candēla and the English route; Kids Etymology explicitly gives Old English candel and the related-word connections.
- Online Etymology Dictionary · candle
Meanings of the older forms on the word path.