I don't understand why nightmode is not a native function include in the FW... all the other manufacturers provide it with their devices

. Indeed when you buy a car there are 2 headlights to drive by night, it's not a option; why it's not the same with a device that has got a light to read in the dark???
For stanlefor : this link
https://github.com/gtalusan/kobo-nightmode is really the best solution to have nightmode and it's very easy to install.
For davidfor : I will try to set the refresh to a large number to see if it's better... It will be something like this in my .kobo\nightmode.ini :
refreshScreenPages = 99
PS : sorry for my bad english... i'm french.