I have been seriously growing Cattleyas under LED lights for at least 5 years. Growing and blooming them is now good, after having studied and experimented with various growing conditions. The lights for my Cattleyas are all ALT brand, either 15 or 20 watts, with 60 degree beam angles. They are natural white and screw into track lighting fixtures. They are more expensive, but they have excellent heat dissipation. I agree with Ray’s calculations. I only use a PAR (photosynthetically active radiation) monitor to assess the amount of photons/light. I do not use more than 300 micromoles/m2/sec at the top of any Cattleya. I use day lengths that replicate what Cattleyas see in the wild, so a maximum of 13 hours in peak summer and a minimum of 11.0 hours in mid-winter. I have an orchid friend in another state who is using the same light levels and day lengths and successfully growing/blooming Cattleyas.