Everything You Didn’t Know You Needed To Know About LED Grow Light Intensity Curves

Accurately calculating light intensity curve of your LED lights determines the best placement of the lights to ensure optimal plant growth. 

 Maximize crop production by taking into account the light intensity curves of your LED grow lights.Gauging the correct placement of LED grow lights is essential to ensure maximum plant productivity. When plants receive optimal light intensity, they achieve greater biomass than those not exposed to sufficient light. Additionally, partial shading of plants significantly increases the risk of leaf deformations, tumors, and issues with fruiting. Given the importance of determining the best placement of LED grow lights, what do you need to take into account when installing LED light systems?The Difference between HID Lights and LED Grow LightsIf you are switching from HPS or HID lighting, the correct placement of LED grow lights can be a challenge due to the differences in the amount of heat the lights emit. Since HID lights generate a great deal of heat, you need to place them anywhere from 1 foot to 6 feet above the plants to prevent scorching the plants. In contrast, LED grow light emit little to no heat, which means you need to install them 4 inches to 24 inches away from the plants depending on the light needs of the plant and the intensity of the light.Accurately Calculate Light Intensity Curves

To determine the light intensity of LED grow light systems correctly, you need to know the following:

  • The light requirements of your plants,
  • The light intensity associated with the wavelengths of light produced by the LED diodes
  • The optic level of the lens used with the LED light system

Regardless of the color recipe of LEDs used in the grow lights, the light intensity curve is always bell-shaped with the 50 percent intensity level at 120 degrees, which is 60 degrees in each direction.

1.2Figure 1. Different wavelengths of light vary in their light intensity curves, which affects optimal light placement.

 

If you depend on this number alone, you will make a critical mistake. Since light travels a straight line along the hypotenuse of a triangle, the light intensity decreases inversely with the square of the distance between the LED and the plant. For example, if a light travels diagonally along a 45-degree angle, the intensity of the light drops by 50 percent by the time it reaches the plant as calculated by 1.0/1.4 X1.4= 1/1.96, which rounded up is ½.

 

To facilitate this calculation, simply divide the relative light intensity curve by the correction factor listed in the table below:

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Using Light Intensity to Determine LED Placement

 

1.4To position your LED lights, follow these steps:

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  1. Check the optic level of your LED lights
  2. Calculate the light intensity at various distances
  3. Position the LED lights at midpoint intensity
  4. Take into account the increase in light intensity when overlapping lights.

 

In addition, consider intra-canopy lighting to further optimize crop production.

 

 

Sources:

Rodriguez, E. (2016). What you don’t know about LED light intensity curves for grow light apps. EDN Network.

Massa, G.D., Kim, H.H., Wheeler, R.M., Mitchell, C.A. (2008).  Plant productivity in response to LED lighting. HortScience 43(7): 1951-1956.