What to do with old spikes

[miakaye]

Thanks, Mateo & Roberta. In the past, I've had success getting a new spike only when placing the plant in a cool window at night, as the night temp in our home is not much lower than the day temp.
I grow my plants under full-spectrum lights. (There is virtually NO sunlight here in Kentucky during winter.) I've been keeping the lights on for about 12 hours a day. Do y'all think that's too long? (The other phal is about to bloom.)