I want to get a mourning gecko

I heard some stuff that if u give them a UVB light they can't eat food with vitamin D3 in it or they will overdose or something on it? If so do I give them a UVB light or the food with vitamin D3? I couldn't really find the crested gecko diet without vitamin D3 so I am tempted to just don't get a UVB light and get that normal CGD. (I don't want to purposefully breed them)