When is it time to move them under lights?

[butterfly_muse]

Just as the title suggests, I am wondering when it is time to move my 'chids from the windows to under lights.

I've got five phalaenopsis, three cattleya hybrids and an oncidium intergeneric. For the moment, they seem to be quite pleased by the light they're getting, but then again, I'm not the plant so I don't *actually* know.

They are all in western facing windows, and I have definitely noticed the sun is getting lower and lower on the horizon - it's whipping around under the trees where it used to be higher and is pointing more direct light at my windows. Thankfully, there are some large trees outside where the phals are so they are not being hit quite as hard, but they're still getting more light than they are used to, I'd imagine.

So when is it the right time to move them under lights and away from the windows?