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Using PAR watts to calculate your lighting requirements

When you are working in a grow environment and need to calculate how many lights you will require there may be a little bit of confusion around the subject. With these simple calculations you will be able to determine the light intensity as well as how many lights you will require in the given grow space.

We will use a 20m x 9m environment for demonstration which gives us a 180sqm working area. Firstly you need to choose the wattage of the lights you want to make use of and also check the PAR watts per sq/m that you will require to successfully grow your plant variety of choice.

In this demonstration we will assume the client wants to achieve a 100-130PAR watts/sqm and have chosen to use 600W lights for this install because it is the most efficient grow light when you compare the lumen output VS power consumption VS yield.

At first a thumb suck of 48 lights for this grow will do, we will base the calculations on this for right now:

  • 48 x 600W = 28800W  

We then divide this by the Sq/m of the grow room:

  • 28800W ÷ 180sqm = 160 PAR watts per sqm.

So now we know how much light we will emit per square meter. You only needs to achieve a PAR watt per square meter of 100-130 PAR.

So now we can reverse this equation by using the required PAR to determine how many lights they will in fact need as follows:

  • 130W PAR x 180sqm = 23400W
  • 23400W ÷ 600W lights = 39 lights

So to conclude, the grower only needs 39 lights to illuminate a 180sqm grow environment.

If you have any further questions please Contact Us or submit a comment below for our community to read and respond to.

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Jabasraja. S - August 1, 2019

How to measure par wattage in lamps…?
Ex. If I have one 600W lamp how to check… Any particular equipment required for this….

Willem Swart - August 1, 2019

Hi ,how many cannabis plants do I plan for sqm and what is the lighting that I need all indoor?

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