Uniformity

Uniformity refers to the fixture’s ability to provide even light distribution over your plant canopy. Poorly designed reflectors can create patterns of light with hot spots where more light is directed. Uniform light distribution provides consistent light levels to plants across the canopy. The fixture comparison image below shows how two different fixtures produce drastically different uniformity coverage results in the distribution from the same lamp.

Measuring Uniformity

Uniformity can be measured using Photosynthetic Photon Flux Density (PPFD) and Photobiological Flux Density (PBFD). These metrics describe the amount of photons present in a specific density at a specific distance. All of these metrics can be misleading if used alone. When looked at together, they can help a grower understand the overall performance of the product.

Maximum, Minimum & Average Measurements

Maximum PPFD/PBFD represents the highest intensity spot.
Minimum PPFD/PBFD provides the lowest intensity spot.
Average PPFD/PBFD represents the average of all data points measured. 

 

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. See image above for an example.

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 max and min PPFD/PBFD.
Avg/min ratio shows the variance between the avg and the min PPFD/PBFD.

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. More data points will result in a more accurate uniformity measurement.

Measured Footprint

The area where the measurements are taken is the measured footprint. It is often used as a recommended coverage area for a fixture. In that case, it will provide a better understanding of how the fixture uniformity would translate across a larger canopy when multiple fixtures are used. The image below shows a 4×4 measured footprint in blue and a 2×2 measured footprint in red. These two footprints show very different results as shown in the data charts above.