Just to let people know I installed nightmode from
https://github.com/traycold/kobo-nightmode
The trick for me was realising that the on screen brightness/home buttons do *NOT* work. You have to set the brightness to the exact level defined in the configuration file
extra/nightmode.ini (default is 12) to enable it. That is I assume because there is not a special hardware light/home button.
A bit tricky with the slider but that worked!
Great!
Andrew