While some users tend to cultivate only one batch of plants at one time, others believe in cultivating different batches, with some undergoing vegetation and others in the flowering phase. Under such circumstances, it is useful to have grow lights with varying PAR intensity ie lights that are dimmable because then these lights can be adjusted to each group of plants (depending on what is positioned where) without having to change the light fixtures.
Spectrum and Blue:Red Ratio
While some users prefer to use white LEDs and others blue/red LEDs, each grow light unit should contain provision for lighting for both the phases. While white lights (5500K color temperature works best) would work for the entire duration of the plant’s life, red and blue lights should be arranged in a manner that either or both can be used at one time, and either or both can be dimmed independently off the other.
Further, users should note that the ratio of red to blue lights should generally be 5:1 or 6:1 because more blue lights are needed to produce the same growth effect compared to red lights.
UV and IR lights
UV lights help improve the natural protection mechanisms that the plant possesses, thereby ensuring that it is better prepared against eventualities. Further, UV lights improve plant metabolism, thereby helping them develop at an increased pace. THC growth is also aided by UV according to some studies. Look for UV lights in the 315-400nm range, though lights below 315nm are also acceptable.
IR lights tend to be important for improving flowering and vertical growth of the plant. They should be in the vicinity of -730nm. While purchasing lights, look for “far red” diodes with the above mentioned wavelength to figure out if the unit has true IR diodes.
Advertised and Actual Wattage
One of the common fallacies regarding high-power LED grow lights is that their advertised and actual wattage is the same. In reality, the actual wattage would be somewhere between 50-75% of the advertised wattage, since the companies can only manage to provide about 550 mA of power input, thus reducing the output that the lights can provide. Hence, when considering actual output vis a vis a HID or fluorescent light, calculate the actual output before carrying out the comparison.
Most LED grow lights have a wattage of 3W (advertised), which is enough to penetrate the canopy of the average adult marijuana plant. Dense canopies, such as those created during the Sea of Green or Screen of Green techniques, require about 5W. However, one should be wary of going further than this, as lights above 5W require substantial cooling, and this may make them hardly less cumbersome than HIDs.
While the high-power best LED grow lights convert only 15% of their electrical input into heat (and the rest into light) compared to 80% in case of HIDs, high wattage LEDs may need heat sinks. Such heat sinks should be fitted to the circuit board, be finned and be made of high quality metal.
Coverage area is defined as the area covered by the light arc created by a single light unit (not a single LED bulb). Small lights can achieve up to 4sq ft. while larger ones easily reach 25sq ft. More importantly, it should be noted that the area covered depends not only on the wattage, but the lens angle. Angles below 60 degrees tend to concentrate light in a small area, and provide high intensity. Hence, they’re good for small, dense canopies. Angles above 90 degrees can cover a large area but the intensity suffers. Some growers suggest an angle of 78 degrees, though there may be some variation from brand to brand.