- Jan 15, 2019
- Reaction score
I need 200-400 micromoles/m2/sec peak photon intensity at the top of Cattleya leaves to get good growth and blooming. You cannot get that with the MR16 bulbs at 3 feet! At the height were the intensity is high enough, you are not very high over the plants and the foot print is not very wide. I only use the 7 watt MR16 for lower light orchids where 50-80 micromoles/m2/sec gets the job done. For Cattleyas I am using 60 degree 15 or 20 watt ALT bulbs at 6-12 inch heights depending on which bulb to get the 200-400 intensity. I would not try and do Cattleyas with the MR16, 7 watt bulbs.
I totally trust your experience and am relying on it. I'm not suggesting I would use the MR16s for cattleyas (ideally). I've actually already replaced the MR16s that were over my cattleyas with my old 2650 lumen spots for the time being. The spectrum isn't the best but a bit of natural light is helping. HOWEVER , the question still remains of rectifying these MR16s with the distance recommendations posted for these lights. Jerry insists repeatedly, against my stubborn skepticism, that these bulbs are effective at surprising distances. I trust him. I just don't understand it and it will bug me until I do.
LEDs register convincingly on a foot-candle meter. When I measure my MR16s with a footcandle meter at 32 inches, I get a reading of about 1500 directly under the bulb. Tagging onto comments Ray has made about downwardly adjusting plant light intensity requirements when converting from natural to artificial light, a constant supply of 1500fc under artificial light for 12 hours every day would theoretically suffice for a plant rated as needing 3000fc of natural daylight. So, maybe the specifications posted for these MR16s are based on footcandle readings and are assuming a constant supply of this light for 12 hours per day making up the other 1500fc. Maybe even extending the time a little bit but I don't think this is recommended.
So, I have a measly 35 micromoles/m2/s at a distance of 32 inches from these bulbs. When I measure natural light at 3000fc, and then measure that same 3000fc with a PPFD meter, I receive a yield of about 70 micromoles/m2/s. Measuring directly under the MR16 with a footcandle meter at a distance of 32" registers about 1500fc (half the first reading under natural light). Measuring the same distance with a PPFD meter yields about 35 micromoles/m2/s as stated. So it seems that the proportion of micromoles/m2/s to footcandles at varying intensities remains constant and also applies to both natural light and artificial light of comparable quality. So given that the proposal is grow plants under artificial light yielding 35 micromoles/m2/s (or 1500fc) at a constant exposure of 12 hours every day, is it arguable that the MR16s would, after all, suit orchids requiring 70 micromoles/m2/s (or 3000fc) in natural light?