How Do Two Lights Work Together in Your Garden? These BPFD Charts Show The Science

BPFD Charts For 2 Lights in a 4×4 Grow Tent are Available

If you read our previous blog on BPFD and PAR values, you have a pretty good idea of what this post will be all about. If you missed that post, or if you would like to read through it again, you can find it here. This episode will serve more as a refresher and an expansion into concepts like bigger areas and more lights working together.


BPFD, PBAR, and Other Scientific Letter Arrangements

BPFD stands for Biological Photon Flux Density. What this typically oblique scientific term means is a measurement of how many particles of light are hitting a certain point every second. But not just any light- no! BPFD is concerned with the spectrum of light that plants use in photosynthesis. More on that in a sec. When you read the numbers in a BPFD chart, you’re basically seeing how many micromoles of light are hitting each of those points on the grid every second. Sunlight can vary widely with how much light we naturally receive, but in general, anywhere between 500 to 1500 is sunlight plants can readily use.

PBAR stands for Photosynthetically Biologically Active Radiation. This is an especially tedious way of saying light plants use. It’s a measure of the light spectrum plants use in photosynthesis. It includes a good amount of infrared light. This is why we use broad spectrum LEDs in our lights. In fact, building LEDs that gave off the full PBAR spectrum is how the Green Sunshine Company came to be!

PPFD, or Photosynthetic Photon Flux Density and PAR, or Photosynthetically Active Radiation are terms that often get used in the growing community because they are built on scientific work done in the early 1970’s. They don’t account for broad spectrum light, are based on outdated scientific models, and were published before women were allowed into ivy league schools or had any voice in science, so their veracity is questionable at best.


When Your Powers Combine

What we have compiled for you here are BPFD charts for two lights in a 4×4 grow tent. If you compare them with the BPFD charts from our previous episode, you will see that there is a significant increase in area covered. Two lights working together are greater than the sum of each individually. 

Our Electric Sky grow lights are equipped with lenses that direct the light downward, allowing your plants to receive all the light produced. When using a single light, this creates a very concentrated area of effect. Using two lights together, however, expands the area.

The identity crisis of light centers around the singular question: is it a particle or a wave? As far as science can tell, it’s both. Cohesion is the tendency of like particles to stick together, and the more dense a cohesion, the greater that tendency becomes. Constructive interference is the tendency of like waves to amplify when meeting. This can be seen in the charts where the concentration of light at very close distances are centered directly below each individual light. But when the distance becomes greater, the light wave-particles have more time and space to merge and stick together, until the greater light concentration moves to the space in between the lights. Cohesion overrides the direction of the lenses given the space and opportunity, and constructive interference amplifies the light intensity where they meet.


What Does This Mean For Your Garden?

Whether you’re growing in a 4×4 tent or a bigger space, the effect of cohesion will be evident when you are using multiple lights together. The area the light will cover between lights placed near one another is greater than that outside the link. You may want to play with the distance between the lights to get the coverage you desire. The lights in the charts were placed evenly through the tent; that is, about 6.5″ from each other and 6.5″ from either side. The effect on light distribution is evident. If you are growing in this configuration, or in one like it, and you have on plant that is growing slower than the others, or one strain that likes more light, you may want to arrange your pots so that the more needy are centered between the lights. The opposite for those who like less light, obviously.


The charts shown here are labeled with heights and lights as recorded. We took readings of two ES300 V3 lights and two ES180 V3 lights at heights of 12 inches, 18 inches, 2 feet and 3 feet. Optimal growing light ranges are colored yellow and orange, with the lower ranges fading to green and higher in red. If you wish to learn more about PBAR and BPFD, please see our previous post that dives into the science behind these numbers here.

Without further ado, here are the charts:











6 thoughts on “How Do Two Lights Work Together in Your Garden? These BPFD Charts Show The Science

  1. John Jackson Reply

    Has anyone done spectrum analytics and have a chart, please. As would like to match up 180 model

  2. Alain Reply

    Thank you for the ppfd chart just bought 2x 180 v3 and a 4×4 tent. Can’t wait to try those new light!!!!

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