Here are the average temperatures in Luxor.
The Egyptian central-southern desert is one of the sunniest places on Earth: clear skies are a permanent feature in all seasons.
Here are the average daily sunshine hours in Aswan.
If you want to visit the archaeological sites of Egypt, such as the Great Pyramids of El Giza, the best time is winter (November to February), when the weather is normally mild and sunny. The temperature range can be high, especially in the south, so much so that it can be warm during the day but even cold at night.
The absolute best months are probably November in the north (Cairo, El Giza) and December in the center-south (Luxor, Aswan).