If you have your orchid in the window and it develops black blotches then your plant has a bad case of sunburn! Longer, brighter days can increase the light intensity in your window so that the leaves get too hot and burn.

You need to move your plant back from the window or put up sheer curtains to help protect it from direct sunlight. As the light intensity decreases in the fall, move your plant closer to the window again. Frequently check their leaves and watch for any fading of their green color, especially on those parts of the leaf closest to the window. This is an early indication that they are being exposed to too much sun.