Lychnapsia in the Egyptian tradition is the Day of the Light of Aset (Isis) held on 12th of August each year. On this day Aset (Isis) is celebrated with all forms of light including sun worship, during the day and candles at night. Interestingly tomorrow is the 3 day Roman festival of light in honour of the Goddess Diana which no doubt was a development from the Egyptian Festival.
Romans incorporated Isis into their own religion as well. There is a Temple to Isis in Pompei to this day.
Further information
Please see https://en.wikipedia.org/wiki/Lychnapsia