What humidity level for storing a collection ?

Hello,

What is the best and most adviced humidity level % (best ones, acceptables ones, dangerous ones ?) to store a lepidoptera collection in a room ?

Thanks by advance for your advices.

Fred

Many thanks for your answer.
Since my post I made some research and it seems that like you said around 50% would be great.
In the winter time during the day I am actualy at 60% and at night it can go till 65-70% would like to lower the humidity level, I will buy a deshumidification machine (since I don't want my spread specimens to move from flat position to a wings up position