Calculate Day Light Integral DLI using a Photosynthetically Active Radiation PAR sensor (also known as a PAR or Quantum Meter)

An excellent way to measure the power of light is by using a PAR meter. A PAR meter measures the photons per square meter per second. It measures how intense the light is in a given location.

This is an image of the PAR meter.

To get a reading, you plug the meter into your computer. And set the par meter down in the location you want the reading. It will then give you a reading onto a software. This particular meter uses Aplgee Connect.

This is the PAR meter in a GBE unit.

The readings look like this:

This is a reading for par in Aplgee Connect.

We 3D printed these special PAR meter holders to ensure that the PAR meter is steady to get accurate readings.

This is the par meter in the 3D printed holder

I tested various locations with the par meter:

  • Sun Outside - 1692.2
  • Outside in Shade - 238.6
  • Under a Lamp - 16.4
  • MARSfarm Office - 11.1
  • In a GBE Unit - 178.7
  • In an MV.1 - 338.6

The Daily light integral (DLI) is the amount of PAR received each day. To convert PAR to DLI:

    1. add all PAR readings; 2) multiply by the time interval in seconds between measurements; 3) divide by 1,000,000 to complete the unit conversion.

OR multiply your PAR value by (based on how long the light time interval):

  • 24-hours: 0.0864
  • 16-hours: 0.0576
  • 12-hours: 0.0432
  • 10-hours: 0.036
  • 6-hours: 0.0216

DLI and PAR values can give you insight into plant growth. DLI can influence the root growth of seedlings and can affect the plant’s final quality.

You can read more about PAR and DLI values at MARSfarm here:

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A new method to evaluate PAR values is with the Photone app for a phone. It uses an existing sensor within a phone to get PAR readings without using an expensive PAR sensor, and it is available on both Android and iOS.

After hearing about this, I decided to compare it to our PAR sensor, which we know to be very accurate. This was done with both inside a GBE FG.V3 box, using a setup posted below:

Setup of a phone running Photone and a PAR sensor plugged into a laptop

Here are my results:

Photone Mode Light Settings PAR Meter Reading (PAR) Photone Reading (PAR)
LED Full Spectrum White 255 640 684
LED Full Spectrum White 175 354 379
LED Full Spectrum White 125 190 205
LED Full Spectrum Red 255 504 318
LED Full Spectrum Green 255 112 128
LED Blue/White Blue 255 371 32
LED Blue/White White 255 638 711
LED Blue/White Blue 175 White 175 483 327
LED Blue/White Blue 125 White 125 282 198
LED Red/Blue Red 255 504 550
LED Red/Blue Blue 255 372 53
LED Red/Blue White 255 639 1175
LED Red/Blue Red 150 Blue 150 416 299

The main point to be taken is that the app does a fairly decent job with white LEDs in the full spectrum mode, overshooting by only around 5-10%. It does slightly worse with reds and greens, at about a 10% error, but it simply cannot be trusted with blues, which it seems to undershoot by a factor of 11 – only measuring about 10% of the true value. This may be an artifact of my phone’s sensor, but it may be inherent to the app.

In summary, this app can provide some value for base-level checks, but for better accuracy, a professional sensor would be recommended.

I hope this brief overview of a new sensor technology was helpful for everyone in their quests learn more about agriculture.


Check out this new video of MARSfarm CEO Peter Webb explaining what a par meter is, and walking through different par values inside our units and around HQ.

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DLI Maps for the United States. These are a great way to learn what the DLI is where you live at any time of year - good talking point and poster to print out for a classroom to discuss light as an environmental variable.


How this map can be used to help students create their own custom recipes for the MV1:

  1. Start by deciding what you want to grow.
  2. Using the known growing seasons, calculate the ‘average’ DLI that the plant would receive during its phases of growth.
    • Use the map in the first link to calculate the DLI for that location and time.
    • For shorter duration plants (leafy greens) this is shorter - 2-3 months. If it’s longer, worry more about the period when the fruit would be ripening - whenever it gets the most light.
  3. Convert that DLI into a ‘recipe’ which can be run on the MV1.
    • This table shows the settings for the three pre-made DLI ‘recipes’ (DLI: 30, DLI: 21, DLI: 17) that you can pick from to run in your MV1: What does a MARSfarm recipe do? What is JSON? (ChatGPT-4 Response) - #4 by Peter
      • Honestly, those three are great place to start for growing any type of leafy green.
      • DLI 30 = too much light for most leafy greens.
    • Keep in mind, the conversion we make assumes plants that are ~6" tall.
      • If you’re growing a tomato or pepper - the DLI will be even higher closer to the lights.
    • Other posts earlier in this thread show what a PAR meter is and how we use it to calculate DLI settings for each recipe.

I just realized how dead the strawberries were in the FG.V2 unit @steven happened to take the photo in - we had definitely overwatered those!
@ben @Jamira @stevensolomon0531 @nathaliemarsfarm

I was working with @Jamira as part of his Supervised Agricultural Experience (SAE) and I had recommended he use the Photone app.

A few observations about our experiences with Photone

  • Never trust the Photone app to correctly measure umol in the blue channel.**
    • For this reason, I recommend not using that channel of LEDs at all.
  • Use the ‘LED Red/Blue’ mode to measure umol for the red channel
  • Use the ‘LED Full Spectrum’ to measure umol for the white and green channels.
  • Do not use Photone to measure the ‘combined’ umol for multiple channels of LED - because of the need to use different modes.
    • This requires that the 4 Amps of power from the power supply be distributed across the LED channels - with room to spare.
    • A good rule of thumb would be to not exceed a ‘knob setting’ of 150 for any of the four channels.
  1. They have a $6.99 paywall (not sure what features require it, @Jamira may have more insight here)
  2. They recommend related products (LED diffuser to improve sensor readings) for their software
  • When @jamira mentioned that the app was recommending he buy a ‘diffuser’ I jumped to the incorrect conclusion that the wrong conclusion that it essentially meant a lamp shade. Instead, what they’re recommending you purchasing is an attachment for your phone to improve the sensors accuracy.

Regardless of the ‘Mode’, Photone fails to measure the blue channel of LEDs

How Photone can be used to compare photoperiods.

Steps 1-2 of this process only apply to the ‘manual knob LED controller’ (shown below) that is used in models FG.V1-V4. @Jamira Upload screenshots from the Photone app as you do this - please! Unfortunately, MARSfarm is no longer an authorized distributor for that product line - so skip to step #3 if you don’t already have one to learn how you can automate these light settings using the software ‘recipe’ that runs on a MARSfarm Version 1!

  1. Settings for 12 hour photoperiod (12 DLI) using white and red LEDs.
  • start by turning red to 100 umol (the number in the photone app, not the # on the controller)
    • write the # on the controller down - this is your ‘Knob Controller Setting’ for red.
  • now turn white up until it reaches 200 umol in the app.
    • write the # on the controller down - this is your ‘Knob Controller Setting’ for white.
  • these become the light settings for your 12 hour photoperiod experiment (set timer accordingly)
    - 300 umol * 60 seconds * 60 minutes = 1.08 mol per hour * 12 hours = 12.96 DLI
  1. Settings for 12 hour photoperiod (12 DLI) using white and red LEDs.
  • start by turning red to 50 umol (the number in the photone app, not the # on the controller)
    • write the # on the controller down - this is your ‘Knob Controller Setting’ for red.
  • now turn white up until it reaches 100 umol in the app.
    • write the # on the controller down - this is your ‘Knob Controller Setting’ for white.
  • these become the light settings for your 12 hour photoperiod experiment (set timer accordingly)
    - 100 umol * 60 seconds * 60 minutes = 1.08 mol per hour * 24 hours = 12.96 DLI
  1. Use the settings for recipe #16 and #17 on this calculator to determine what the equivalent MV1 settings would be.

Your measurements of FG.V1-V4 using Photone should be similar to these

Evaluating the Photone app quality and its value to this community

I found a ‘Plant Light Database’ on the Photone website - the measurements line up with normal recommendations I’ve seen elsewhere but this is one (if not the most) comprehensive databases of lighting recommendations I’ve found. They seem to be pretty open and motivated by getting views/afilliate ad money - I’ll be reaching out to see about collaborations but want to do a bit more digging first. Here’s a few places I plan to reference in the future:

@jeremy.hall @wxazygy it would be helpful to have another ‘expert’ or two collect comparable data here. Since there are ~1,200 FG-V1-V4 models in schools right now - creating a calculator (similar to the MV1) for those models of hardware would be a valuable addition to this community.

@hmw Would you be willing to take a few minutes to look into what/anything you can find about who makes Photone and how it works? I’m interested in better understanding the hardware it uses and any variations we should be aware of in terms of hardware (Samsung vs LG, etc.) - do the sensors vary at all? Any guesses on why blue stinks? Does it use the camera or the ambient light sensor? What changes based on the ‘mode’ setting? How could we create a similar ‘mode’ using an ambient light sensor that would convert the white light from an MV1 into umol?

Photone is made by LightRray, a Swiss company.
Photone used the camera to figure PAR. While they have calibrate the software for the iPhone, any other phone requires calibration against another accurate device (PAR meter, or calibrated phone). I suspect this is your blue LED issue, you need to calibrate the phone. Every different (brand/model) phone needs its own calibration. Likely you can take your PAR meter and get a reading of each light channel, then anyone should be able to set their phone to that ‘known’ reading (assuming your light units would all give the same reading).
Not sure what you mean by ‘mode’, the only reference I see is to the ‘modes’ in the professional level that let you do average readings (over time), or use the level to get accurate readings (light directly hitting the camera sensor), or is this the light source (type of ‘bulb’). I see that they sell a $26 diffuser to put over the camera that only reads direct light.
Let me play with this. Assuming I have a Batch 1 (v0.2), I will try calibrating my Motorola and Samsung tablet. to the values you list above (White 286.3 Blue 14.4 Red 55.8)

Critical question: What distance from the lights are you using for measuring? Without a consistent distance, there is no consistent comparison. I think I will use 50cm for now.

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Do you mean 50 cm from the LED? For the MV1 I believe we measure at 12" from the bottom. With the manual knob controller models / manual irrigation it’s probably closer to 4". @hmw we 3d printed a holder for our PAR meter that can be adjusted for this purpose. The most important distance to measure is ‘germination height’.


By mode I meant how they let you switch between ‘Full Spectrum’ and ‘Red/Blue’. It seems like they’re recalibrating their conversion equation based on that user selection.

@Jamira was the one who first brought the diffuser to my attention. The Photone FAQ claims its only necessary for iPhones.

Here’s a link to the video they recommend for how to build your own diffuser:

This is super helpful!!! Thank you for sharing this.

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