Deciduous Dendrobium winter rest

[Jakob]

Hello!
As it is slowly time for these guys (in my case D. aphyllum) to go dormant;
(I'm not at home and i got a rather panicked message from my sister that the big orchid in the cherry tree is getting yellow leaves... i forgot to tell her it's going to do that )
; I wonder how much light do they need in dormancy?
I persume i can't put it in darkness for three months, but can it stay in a badly lit halway, or does it have to get more light?