Choosing the right LED requires more than a PPF number

To help explain, we will use this concept LED fixture. It packs a punch, but is it the right punch?

PPF: 2000 μmol
Efficacy: 2.96 μmol/J
Watts: 675

(All data shown is taken from the concept LED on display here)

WHAT YOU NEED TO KNOW WHEN COMPARING LED PRODUCTS

1 Spectrum What energy will my plants receive?

2 Intensity How much light is being provided?

3 Uniformity How consistent is the light intensity over the coverage area?

4 Efficacy How efficient is the system? Is this important for plant growth?

Understanding Spectrum

Spectrum

The quality of the light energy.

Different segments of the spectrum affect plant growth in many ways. A PPF number does not represent the entire quality of light an LED will provide. PPF only measures the portion of light spectrum between 400 and 700 nanometers.

Understanding Intensity

Intensity

How much light is being provided.

Maximum, Minimum & Average Measurements
Maximum PPFD number only represents one data point under the entire fixture.
It provides the highest intensity spot and can be misleading if used alone.
Minimum PPFD number only represents one data point under the entire fixture.
It provides the lowest intensity spot and is needed to calculate uniformity performance.
Average PPFD number represents the average of all data points measured.
It is needed to understand the overall performance of the product.

Height Above Canopy
This number represents how high the fixture was when measurements were taken. The height
above the canopy directly impacts all intensity measurements and the overall system performance

Understanding Uniformity and How It’s Measured

Uniformity

How consistent the light intensity is over the coverage area.

Uniformity Ratios
Uniformity ratios show how consistent the product lights the plant canopy under the stated coverage area. A perfectly uniform light will have a ratio of 1/1. The closer these ratios are to 1, the more uniform the product lights the canopy.
Max/min ratio shows the variance between the maximum and minimum PPFD.
Avg/min ratio shows the variance between the overall average PPFD and the minimum PPFD.

Number & Placement of Data Points Measured
Data can be manipulated and misleading by measuring a small number of data points or only measuring under the center of the product, as shown in the example to the right.

Measured Footprint
The area where the measurements are taken is the measured footprint. Knowing the measured footprint will provide a better understanding of the performance throughout the total canopy.

Understanding Efficacy and What it Doesn’t Represent

Efficacy

How well the fixture converts energy into PAR photons.

Any beneficial light energy outside the 400-700nm range (eg: UV or Far Red) will reduce the efficacy number making it look less efficient.
In reality, energy outside the PAR range is beneficial to plant growth, especially cannabis.

Conclusion

These four factors will help you make an educated purchase:

1. Spectrum is the single most important feature when choosing any grow light. The quality of light can have dramatic affects on plant quality and yield.

2. Intensity is key to successful plant growth yet can be very misleading if it is the only metric considered.

3. Uniformity is the ability of the product to evenly distribute light over the canopy. It must not be overlooked.

4. Efficacy DOES NOT represent the full capability of the lighting system and can actually understate its growing capacity.