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How to Increase Grow Light Intensity

To put it simply, light is an extremely important factor that affects your yield. The quality and quantity of your grow light can make or break your grow. Amateur growers mistakenly believe that to optimize the amount of light in their grow space, they need to add more lamps.

The issue here is that aside from consuming more electricity, additional grow lights mean a lot more heat. This was how the idea of using reflectors was hatched. However, a lot of beginners ignore reflectors or do not use them properly.

In this article, we show you how you can optimize the positioning of your reflectors so that you boost plant yield while minimizing waste of light and generated heat.

Some Handy Units

First of all, the DLI (daily light integral, unit: moles/day/m2; used to determine the light requirement of a certain plant) required by marijuana is unknown. The rule of thumb is to guarantee at least 25 moles/day/m2, which translates to an hourly DLI requirement of 1.38 moles/hour/m2 (assuming an 18-hour light cycle).

To get the required PPFD (photosynthetic photon flux density, unit: μmol/s/m2; used to measure light intensity), divide that number by 0.0036. This gives you 385 μmol/s/m2, and that is the light intensity you need from your lamps.

Installing the Reflectors

There will be some trial and error involved going forward, but at least you know what numbers to look for. First, use a spectroradiometer and ensure that your plants’ canopy are getting all the light (read: sufficient μmol/s/m2) they need. This is why putting reflectors on the walls is not enough. The light has to be concentrated on the canopy itself for your plants to gain any actual benefit.

To give you some perspective, a 400 W cool-tube HPS with built-in reflector can produce a PPFD of 148 μmol/s/m2 covering up to 3 ft under it. This number can go up to 235 μmol/s/m2 by putting reflectors on both sides of the lamp such that light was concentrated on the floor at 120°.

Your goal is to force the light into the tightest possible angle. This is what increases the PPFD that goes on your plant canopy and eventually boosts your yield.

A Quick Summary

In summary, have a handy spectroradiometer around, and invest in true reflectors. Put up those reflectors around your light such that your plant canopy is getting 90% to 95% of the light, and check the PPFD on the canopy to see if you’re doing the right thing.

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