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they are built on scientific work done in the early 1970’s. They don’t account for broad spectrum light, are based on outdated scientific models, and were published before women were allowed into ivy league schools or had any voice in science, so their veracity is questionable at best.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:











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

  1. Jarwin Reply

    I have 2x es180v3 in a 5×3 do I place them side to side vertically or straight line horizontal for best coverage?

    • [email protected] Reply

      Our recommendation for lighting a 3′ x 5′ tent is one V3 ES300. This will give you perfect edge to edge coverage. If you are going to use 2 V3 ES180s, we would recommend running them end to end. You will be short 6″ on the two 5′ walls but you wont risk PPFD hot spots with hanging them too close together side by side.

  2. Claybo Reply

    Those photos are very helpful, I have two ES 180s in a 3×3 733 AC infinity tent with all the “bells and whistles” that can be applied other than CO2 injection. They are spaced about 2/3 inches apart and about 5 inches or so from the right and left walls. I have four plants that are just about ready to flip to 12/12. But obviously I can’t put them in the center, and yes they are getting huge as you’re lights are doing a great job. The lights are approximately 18/20″ from the plants depending on which plant as they are different heights. (they were transferred from another vegging’ set up when about 13″ and I adjusted the lights and started at about 36″) I’ve been monitoring the leaves especially at the tops for any brown tips or canoeing for signs to raise the lights but haven’t had any signs so far. I’m going to push these plants another 5 to 8″ higher before I flip. The tallest one is 23 inches currently. This is my second grow, my first with the Electric skies and they are doing an incredible job. The first grow was with an HLG 260W QB Rspec led and only one for three plants in the tent. It did a great job considering, and must say it is also a very good light but yours is definitely the way to go, the HLG is in another grow tent I use for vegging and cloning. All in all I just wanted to say your lights are definitely the best on the market and are a necessity if you want to lead the grow community in professionally grown cannabis. Your lights were by far the best investment I’ve made in this entire journey. Thank you for all the tests and time you spend researching the light values. I hope to get more emails from you with professional guidance and tips and tricks of the trade, thanks Dan!
    (*hope I win that ES 300:)

  3. John Jackson Reply

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

  4. 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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