Most people will tell you it depends on the type of Bulbo. This is good advice but one thing to remember is you should never be afraid to experiment on how much light your plant can handle. Just remember to give the plant time to adjust. This past Summer I placed my Bulbophyllum echinolabium on my deck. By July it was getting hours of full sunlight with no shading at all. This is more light than most would recommend for this plant. It now has four spikes and is growing two new leaves. Give your orchids as much light as they can handle and then pull back a little.
Usually rule for bulbos, is strong enough light to create a good shadow on your plants if a hand is held between the plant and the light. No direct sun is recommended. It would also depend on how close you are to the sun. The worst sunburn I ever got was in Pa after living on Florida beaches all my life. Slowly adjust plant to stronger light.