That oncidium falls into the psychopsis gang.
In general they can handle varying degrees of light and prefer a medium that drains fast but frequent watering.
The leaves may be able to give you an indication on the light levels.
If the leaves are all green but healthy, then it is getting just the minimum amount of light that it needs.
If the leaves produce a very vivid mottling of green and purple on top (and the bottom turns purple with green dots) then it is getting sufficient light.
In my greenhouse (50% humidity most of the time), I was able to achieve this mottling on another psychopsis at around 3500fc-4000fc. Anything more and the leaves start to wilt.