Welcome to OrchidTalk. Oncidiums and miltonias need filtered sunlight, not direct sunlight. They will appreciate bright shade.
Here is a copy/ paste from our care guide here at RVO.
1500 - 2000 footcandles
A bright kitchen window with no direct sun is perfect for these medium-light loving lants.
70 - 90 degrees F. daytime, 60 - 65 degrees F. night.
40 - 65 % relative humidity is ideal.
In general, Oncidiums and the intergeneric hybrids produced with them form sprays sometimes over four feet long of tiny, often yellow or pink-tinted flowers that can make quite a show. Almost all are fragrant. They grow quickly, and it is not unusual for new pseudobulbs to stair-step their way out of a pot, throwing thin roots everywhere. These can be misted with fertilizer solution diluted from 1/3 to 1/2 strength each time the pot is watered. Oncidiinae appreciate good air movement. Plants that receive sufficient light to flower often exhibit scores of tiny brown spots on the leaves and their leaf-tips frequently turn yellow. The leaves themselves can be quite brittle and will split naturally during normal growth, so the foliage is usually not considered particularly attractive. Equitant oncidiums can be difficult, as they require a cool spell at the end of the growing season to initiate the next years flowering.