Light

PAR stands for Photosynthetic Active Radiation, or light available for the plants to use for photosynthesis.  PAR can be measured with a PAR Meter allowing us to measure accurately, and adjust the light to get the optimum growth on our plants.

PAR meters and sensors have been around for years and have been used accurately for sunlight, fluorescents, and HID grow lights.  Recently with the tremendous growth in LED lighting used for horticulture, these sensors have been re-designed to read the spectrum of LED light more accurately than that of the older sensors.  Apogee is a leader in light meter sensors, and they have now published a conversion factor for the old sensors to give an accurate approximation of the light from various LED sources.  This means that older PAR meters can be successfully used to measure our LED grow lights.  These older meters with sensors can be found used online at a much lower cost than a new meter with the new sensor. 

For my stem props and seedling flasks we grow under about 100 PAR.  We are currently using the 2'X4' LED flat panel drop in.  

In the greenhouse, I find that the plants grow the best at 150-175 PAR.  Phalaenopsis can take more light as long as the temperatures do not get too hot.  Strive for medium green leaves.  Dark green not enough light, yellow green top end of light intensity.