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LED grow lights are environmentally friendly first of all and the foremost advantage. Quick start, low power, no flash are the advantages which save energy. So now energy is secured. Again if using LED grow lights then the photosynthetic effect of plants will increase, the growth rate of plants will increase when regular lights can’t do that. The followings are the tips of how to choose a best LED grow light: 1.Spectrum, PPF &PAR&PPFD PPF (Photosynthetic Photon Flux) is the key measure for grow lights as they measure the total amount of PAR (Photosynthetic Active Radiation) that is produced by a lighting system each second. PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis. This is essentially the spectrum of light your plants actually use and need. Beware that if the LED light you are considering makes no mention of these anywhere then dig in a bit to understand whether their wattage actually caters to the spectrum your plants need. A lot of lights claim to be full spectrum, however, as we mentioned above, plants need a certain wavelength and this is critical for their growth and during vegetative and flowering stages. Make sure you find out what the PAR is for light you are evaluating and what the density of that PAR based on PPF values. SPECTRUM: For efficient photosynthesis, plants require different light wavelengths, or spectrums, at different stages. To supply suitable light spectrums at each growth stage, you may have to use different LEDs that produce specific color spectrums. If you choose full spectrum LEDs that allow customization of spectral light, or have full spectrum built in, it allows the grower to have the correct light for full cycle cultivation from seedings to harvesting. For example, in order to grow most efficiently, many plants need light in the red and blue spectrum, but also infrared and ultraviolet, depending on the stage. A powerful full spectrum LED grow light enables you to cater to the plant's specific needs by providing the proper photosynthetically active radiation values. PAR： PAR is photosynthetic active radiation. PAR light is the wavelengths of light within the visible range of 400 to 700 nanometers (nm) which drive photosynthesis (Figure 1). PAR is a much used (and often misused) term related to horticulture lighting. PAR is NOT a measurement or “metric” like feet, inches or kilos. Rather, it defines the type of light needed to support photosynthesis. The amount and spectral light quality of PAR light are the important metrics to focus on. PPF: PPF is photosynthetic photon flux. PPF measures the total amount of PAR that is produced by a lighting system each second. This measurement is taken using a specialized instrument called an integrating sphere that captures and measures essentially all photons emitted by a lighting system. The unit used to express PPF is micromoles per second (μmol/s). PPFD: PPFD is photosynthetic photon flux density. PPFD measures the amount of PAR that actually arrives at the plant, or as a scientist might say: “the number of photosynthetically active photons that fall on a given surface each second”. PPFD is a ‘spot’ measurement of a specific location on your plant canopy, and it is measured in micromoles per square meter per second (μmol/m2/s). If you want to find out the true light intensity of a lamp over a designated growing area (e.g. 4’ x 4’), it is important that the average of several PPFD measurements at a defined height are taken. Lighting companies that only publish the PPFD at the center point of a coverage area grossly overestimate the true light intensity of a fixture. A single measurement does not tell you much, since horticulture lights are generally brightest in the center, with light levels decreasing as measurements are taken towards the edges of the coverage area. 2.Area, Space & Light Footprint This is another very critical point to consider when evaluating your light. The footprint or the area that your light will cover will determine how many sets of light you need for your growing area. The lower cost lights tend to not have this information and a lot of beginners find mediocre results with their lights as a result. The footprint of the light is most often mentioned especially in the higher quality lights and gives you a good idea of the area or spread of the light based on the height it is placed. This also makes your PPF values differ and hence good lights and companies do tend to share all this necessary information. Make sure you know how much your growing area covers, and whether your light will be sufficient for it. So consider, light footprint as well as light PPFD for maximum results. 3. Wattage & Efficiency Watts is the measure of the energy input that a light requires. The output of the LED light is not only the function of Watts but also the quality of other components and design. The components are may be: LED chip Chip density Optics used Heatsink The increase of wattage decreases LED efficiency because of the increase of the temperature in the electronic circuit board. So when the manufacturer of LED grow light claiming Watts as the measure of ability to grow plants then it’s suspicious. So you need to have much knowledge of Watts and PAR and must depend on manufacturers’ information. LED chip You always want to look for chips that are at least 3W, any less than that won’t give your plants enough consistent light coverage. This means each chip needs to be 3W, not 3 lights of 1W LEDS, so look out for that when reading the description. The 3W chip offers the best quality in whites, blues and reds. The Output This is also important; you want to read product descriptions for total output. How many units does the lamp claim to have? This can be 300W, 400, 600 or even 1000. Always check for the output and look for at least 300W. The Lens Good quality lamps will have an optical lens that magnifies the light giving about 25% more penetration of nutrients for the plants. This makes for a more expensive lamp but certainly worth the price. Heatsink These lamps stay on for the better part of the day, often 15 hours at a time, so you want to make sure they have internal fans that protect the lamp but also those that protect the plants. If it gets too hot in there you could damage your plants. LED lights run cooler than HPS bulbs as they only let off about 15 to 25 % of the energy as heat, but the heat occurs behind the bulb in LEDS, and that area needs to be protected. A good quality lamp will have a thick aluminum heat sink attached to the back exterior or interior area which forces the heat away from the chips. Materials The LEDs should have a warranty. In fact, LEDs of this nature are supposed to have a life span of about 10 years, especially in some of the more expensive panels. Look for panels that are sturdily built with aluminum, steel or materials that won’t easily break. The Guarantee Look for lamps with more than a one year guarantee, as I mentioned before, LEDs are made to last up to 10 years, so I am somewhat suspicious of manufacturers who only offer a one year guarantee, as this is an indication of a cheaply made housing or cabling system. I usually look for a 3 year guarantee on parts. The parts guarantee is better anyway because the lamp will continue to work regardless of the part that needs replacing. You can easily replace the missing part yourself when it arrives, and in the meantime your plants still get the nutrients they need. Hopefully, this gives you some insight as to what to look for when considering the different LED grow lights for your new marijuana crop.