I filled the metallic channel in unity standard shader , but make object looks very dark … What is the reason?

PS: All my scene lights are baked area light and a very weak ambient color light…
I filled the metallic channel in unity standard shader , but make object looks very dark … What is the reason?

PS: All my scene lights are baked area light and a very weak ambient color light…
tried adding reflection probe, or some skybox image?
Not tried reflection probe yet. A skybox image had been added,and my game scene is a closed space like office ,is this will have an impact ?
I had added the reflection prode,kinda working,thanks very much.
I am adding a reflection probe group for my scene,and what is the best way to bound a reflection probe,a reflection probe for each closed room or just a fixed size area?
i dont have much experience on those, usually i just stick 1 per room (with box reflection enabled..) : D
Add a reflection probe (size:10000x10000) to cover the whole scene
And add other reflection probes for each room