For the northern hemisphere, south facing windows have the brightest light. The intensity will vary throughout the day, peaking at midday.
In Summer, the intensity of south facing windows can burn some orchids. Cattleya are moderate-bright light orchids and at this time of year will be able to stay in a southern window all day. In summer months, you might put them a bit further back from the window to avoid burns. If slowly acclimated to your light by staying there all year they might tolerate it (I have burned cattleya's in southern light in the UK - but they were new so I'm not sure how well acclimated they were to bright light).
The aim is for light green, almost yellowish, foliage on orchids. If they are a lush dark green then light is possibly insufficient (some orchids are naturally darker than others even within the same group).
I think your cattleya's will do fine in your southern window.
Northern windows have the least light and are only good for the lowest light orchids (even then, East/West is probably better where possible). East/west are somewhere in the middle and suitable for most orchids.
If you hold your hand above the orchid, about 1 foot away. If the shadow is cast over it but is blurry, that's a moderate light. If the shadow is sharp and defined, it's bright light. I found that system more helpful than trying to measure it with a meter. It will be constantly changing throughout the day and through the seasons. Hope this helps.
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