soheil_hooshdaran wrote:I even don't know what is a "lux."!
It's a measure of illumination.
https://en.wikipedia.org/wiki/Lux
The wiki suggests that "office" lighting would be a maximum of 500, whilst Stewart's tournament suggestion or recommendation is 800. I've almost certainly played with less, sometimes you just have to remember where the Black pieces are.
Rooms can be deceptive, last weekend at the Hull Congress taking place in the University, there were plenty of light fittings, but they appeared to have been fitted with the lowest powered bulbs possible. Natural light from the windows made it OK on the Saturday and Sunday rounds, but the Friday evening round was decidedly gloomy. The organisers are aware of this and have an alternative room in mind for next year.
The only venue I know that could be too bright was the Horntye Park Sports Hall in Hastings. This was set up with enough illumination for indoor cricket and less lighting proved necessary for when the Chess Congress is held there.