nz ------ I know that growers in the past (and probably even now) use physan - a disinfectant.
If you do choose to use it, the physan 20 site reckons 2 teaspoons per gallon, which comes out to around 2.6 mL physan 20 liquid per 1 litre of fresh water.
I don't use physan 20 for orchids though, even though I do have physan 20 - but never used it heheh. Actually, the bottle says SA-20, but pretty sure it's the same thing.
For your case, if you have non-systematic fungicide like mancozeb, then could try that. Or if you need to use a systematic - could consider monterey garden phos, or copper spray (for orchids and plants), or cleary's 3336 - thiomyl.
At the moment, you probably don't need to apply anything at all. If not provided already, then provide some gentle air-movement to cut down on or eliminate chances of fungal/bacterial activity on leaves.
And if you notice the lighting levels have been a bit high, then just put the orchid in a spot with slightly less maximum light intensity.
Monitor the orchid's condition. If the spots don't spread, and the just dry up (or remain dry), then you will probably not need to apply any disinfectant or treatments.
How long roughly had this orchid been growing - in the particular area that it is currently growing?
Also ---- nz -- at least some of my orchids growing semi-outdoors gets spots like that too on some leaves. No issue with those particular orchids. It's just a part of growing semi-doors (for my orchids that is). So black spots aren't always a problem! Orchids in the wild do get it too - eg. if something happens to bite on it, or the sun gets a little too intense - or something. All part of living outdoor or semi-outdoor.
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