If you are a serious orchid grower and..

[Discus]

You can also use cameras and the EXIF data on your digital pictures to work this out, particularly if you take a picture of a "neutral" coloured object.
Orchids on a Balcony: New Gadget: Light Meter
I collected some common foot candle requirements for orchids on that post.
There are free apps too, but I don't find they're as accurate as cameras.

The formula to work out foot candles from a camera is:

6*F^2/(I*E)

where F = F stop (aperture)
I = ISO setting
E = Shutter Speed (exposure)