What is a safe distance from light (t4 16w) for paphiopedilum?

[weta]

Hi all,

This is my first post.

I have just set up some lights to supplement a northerly facing window (southern hemisphere). However, sun doesnt reach the orchids (even in winter) because of a balcony.

I have quite a few paphiopedilums and was wondering as a generalisation what would be a safe distance to set them from an overhead light where they would benefit, but not be burned?

The light in question is small and is a 16W linkable T4 with a 6400K TriPhosphor tube. I dont have a light meter at the moment, so it would be great if someone could give me an estimate of the distance from the light til I get one.

Thanks
Mike