The new growth on some of my cattleyas turns black at varying stages, sometimes initially and sometimes later. The plants still looks healthy overall, and might still produce flowers later. I grow orchids well outdoors on the California coast in a protected patio.
This might have any one of several causes. Most probable, based on your description, is that you leave the lights on in your patio at night, and this interrupts the dark cycle, resulting in the burned tips. Otherwise, some sort of fungal or bacterial rot is the culprit, and this is best treated with a copper-based compound such as Kocide or Phyton 27 following label instructions.
Also see Blasck Rot