I live in often sunny Florida and sometimes read outside in direct sun. I always try to hold screen at angle giving best screen contrast without sun reflecting off screen into my eyes. Direct sun at some angles can interfere with IR page turns. Some have posted Sun can overheat Kobo readers so they stop working until they cool.
Eink displays are not made by Kobo and it seems like Kindle had one year exclusive on newest Carta Displays.
http://www.eink.com/
http://en.wikipedia.org/wiki/E_Ink