| Let me chime in here and add that it is not necessarily the amount of light received at any one time during the day that makes the difference but rather the TOTAL amount of light received by the plant. For example, let's say that I have my Oncidium outside where it receives 3 000 fc for 8 hours. That's a total of 24 000 fc. Inside, under a 4 tube fluorescent light, it receives 1 500 fc during 16 hours. That's also 24 000 fc. This is usually why lights are on longer than the actual daylength. Let's also remember that the advantage of artificial lights, fluorescent or HID, is that the light intensity is stable over the entire day, whereas natural light will fluctuate naturally, when clouds go by for example, reducing that total 24 000 fc.
Julie |