How to Measure a Grow Light - PAR (Photosynthetic Active Radiation) Ratings Explained

PAR is essentially a measurement of light emission within the photosynthetic range of 400-700nm.  This is the area of light in the color spectrum that plants use for photosynthesis. PAR is measured by the amount of micro moles of light per square meter per second.  But a PAR reading only tells one part of the story.  There are many areas within the PAR scale which plants only absorb in small quantities, such as in the green range (560 nm).  Thus, a reading of a light’s spectrum must be used in conjunction with the PAR reading to determine from what bandwidths those micromoles are being generated, and in what amounts.  A spectrum reading is obtained by using a piece of equipment called a spectrometer.  These two readings (PAR showing strength, and spectrum showing that this strength is in the proper wavelengths) are required to give a complete picture of a grow light’s effectiveness. HID's have good PAR readings, but when their color spectrum is measured we find they emit most of their energy in the wrong spectral areas, making them inefficient for photosynthesis. LED grow lights, on the other hand, have high PAR ratings as well as an optimized spectral output which greatly enhances the efficiency of the light. But not all LED lights are created equal. There are many manufacturers selling grow lights boasting fantastic spectral readings (and pretty charts). The question is how many of these lights have had their spectral graphs verified? In my opinion almost none. There are many inexpensive grow lights on the market which at first glance look like a great buy, but what are you actually getting for your money? 
You will save money up front but in the long run the use of an inefficient light will cost you more in electricity. As well your crops will suffer from the inefficient distribution of spectral wavelengths.

You know the old saying, "You get what you pay for".

 HyperGrow Spectral Graph

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