I've heard three professional growers say that extensive research shows hybrid Phals produce the most and the biggest flowers at no more than 1,000 foot candles of light, with a 10-12 hour day length. Increasing this to no more than 1,200 fc for 6 weeks in late fall may trigger budding, but after the 6 weeks they should be returned to 1,000 fc to improve flower count and size.
People have trouble flowering them in northern climates not because the light intensity is too low, but because the day length in fall and winter is too short. Phals in habitat are almost all deep shade plants.
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