I. Definitions
Imbolc was a pre-christian pagan festival celebrated by the Celts early in February (the date was moveable according to the lunar phases). Today, Imbolc is still celebrated by neo-pagans and celtic reconstructionists, but most people chose the fixed date of February 1st.
Candlemas is also called Presentation at the temple, and for Christians it marks the Purification of Mary after Jesus' birth. The Jewish tradition had it that new mothers were to be purified at the temple 40 days after the birth of their child. It is celebrated on February 2nd.
II. Relation between the 2 festivals
It is not new that early Christianity appropriated various dates and themes of pagan festivals, as well as worship places, in order to facilitate the establishment of the new religion.
If the presentation at the temple was not "invented" to replace Imbolc (this presentation was an old Jewish ritual as said above), it's interesting to notice that both festivals share common themes. Again, contrary to what I read too often, in this case the main theme in question (purification) is intrinsic to the Christian festival and was not "stolen" from the pagan festival, but rather the festival swallowed up folk rituals (details below).
The name Candlemas refers to candle being blessed and then taken home as protection by Christians. According to Pope Innocent XII (17th century) the pagans "
He considered that the association of candles with the Presentation at the temple (hence becoming known as Candlemas) was an appropriation of a Roman (Ceres being a Roman Goddess of agriculture and fertility - of the land and by extension of people) pagan ritual.
