We hadn't anticipated just how hot the sun woulld get in Luxor and although we took two full bottles of factor 50 sun block we soon ran out. I went to a local chemist and bought some Nivea factor 60 and it was quite expensive. We all applied it and then we all burned for the first time on the holiday. I'm not suggesting for a minute that it wasn't Nivea but I don't know how long it had been in stock. All I know is it didn't work. Luckily one of the other guests in the hotel had a spare bottle so we were ok but my tip is bring a lot of sun block with you. This isn't Greece or Spain or Italy it's much, much hotter and you will use a lot more.
Don't worry about not getting a tan with a factor 50 sun block either. In this kind of heat you still will!
I was in Luxor in late June and heat from the sun was fierce. In the middle of the day it was hitting 55c in Luxor and hotter still over on the west bank in places like the Valley of the Kings. You have to go sightseeing at about 6 am and be finished for 10:30 am at the latest. Even if you have to go back to see something you missed it's better than forcing yourself to stay in the heat of the day.
Drink water all the time you are out, wear something on your head and get a high factor sun block on your exposed skin.
The temperature of the hotel pool was even hitting 34c at noon and that is hotter than the air temperature of most northern european countries gets in summer.
It was hot in southern Egypt in April 2008, a high around 40 or 45C, over 100F. I saw several senior people faint in the heat, so be careful. It is very dry and you may not realize your body is lousing so much water.
During summer months, the heat can be unberable! As I have told you, it was 50 C when I went. You must be very careful. Bring water, a hat and a white shirt with long sleeves! Don't go to Luxor without these items...%v*
When we visited Valley of the Kings in August temperature was +65C. Can you believe it? In Luxor it was hot too but not so hot like in Valley.
So take a lot of water with you and wear lightweight cottons and linens (white is best) and something on your head.
It was, maybe, more the 50 degrees, or it looked like that, when we visited Luxor. And it was begining of September. Imagine how it looks like in July.
Take a lot of water with you.