# All the questions at once 😆

As a seedling I run around 20 DLI. Then I slowly raise it up till I’m around 35-40 for most the veg cycle. Then I hold about a 40 through the flower phase too.

@HeyJB what does that mean sorry my 1st grow 2 plants

What light are you using? Sorry if I’ve asked that many times already.

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Vipar1000 @HeyJB

Try downloading a photone app on your phone. Or an app that wil allow you to use your phone to test for DLI. This is a amount if light your plant will receive over a given amount of time. The app will do the math for you so you wont have to do it yourself.

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Lets call in some big guns then. @beardless @Graysin @Fieldofdreams can you assist please? Need to determine DLI without using the phone app.

Hm, do you have an iPad, tablet, or Kindle with a front facing camera? Any of those should also be capable of downloading Photone.

As far as other apps, I haven’t tried anything else. My understanding is the daylight/sunlight setting on Photone is the only tried and true “close to the Apogee meter” app we have to recommend.

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Does the light manufacturer publish a PPFD report? With that and your trusty pocket calculator you should be able to ballpark it. I plugged “Vipar1000” into a search engine and found this one we can use as an example. ViparSpectra® P1000 100W Infrared Full Spectrum LED Grow Light:

``````# MS is microseconds/hour
MS = 3,600 ÷ 1,000,000
1006 PPFD × 18 HOURS × MS = 65 DLI
786 PPFD × 12 HOURS × MS = 34 DLI
``````

To figure out the PPFD for different heights we need the inverse-square law.

``````# 1 unit equals 12 inches, 1.5 = 18", 2 = 24", etc.
1006 ÷ 1² = 1006 PPFD
1006 ÷ 2² = 252 PPFD
``````

Now we can double check their work on the 786 PPFD at 14" height.

``````1006 ÷ (14 ÷ 12)² = 739 PPFD
``````

Close enough for me. So to wrap it all up lets figure out the DLI for 16 hours at 18 inches.

``````1006 ÷ (18 ÷ 12)² = 447 PPFD
447 PPFD × 16 HOURS × MS = 26 DLI
``````
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Is Poly short for Polytechnic.

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I will save this info forever.
My phone doesnt have the reqs for photone. But i can do math.

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Well great job… thank you. Thats the light that i have for my plant… but idk how to read that lol this is my 1st grow… and i have that light on at 65% at about 18-20" away 24hrs a day

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Ah. Can’t help with login info. Once many moons ago I did tech support but it’s been a long while now.

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This post will get you acquainted with PPFD and DLI.

Understanding that will help with the math.

Once you throw dimming into the mix things get even more ballparky since potentiometers have some slop but you could change `1006` to `1006 × 0.65` (or 0.75 for 75% etc) and probably still be close enough.

``````1006 × 0.65 ÷ (18 ÷ 12)² = 291 PPFD
291 × 24 × MS = 25 DLI
``````

Say you decide to raise the light to 22" at 80% for 21 hours a day you would find your DLI like:

``````1006 × 0.8 ÷ (22 ÷ 12)² = 240 PPFD
291 × 21 × MS = 18 DLI
``````
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@Bonjoyle here is an interactive version.

``````<!DOCTYPE html>
<html lang="en-us">
<title>DLI Estimator</title>
<meta charset="utf-8" />
<meta
name="description"
content="Estimate DLI from PPFD reference charts"
/>
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta
name="theme-color"
media="(prefers-color-scheme: light)"
content="white"
/>
<meta
name="theme-color"
media="(prefers-color-scheme: dark)"
content="black"
/>
<style>
body {
}
fieldset {
margin: 1rem 0;
}
</style>
<body>
<h1>DLI Estimator</h1>
<form>
<fieldset>
<legend>Reference values</legend>
<p>
<label>
<input
id="ref_ppfd"
type="number"
min="1"
max="5000"
step="1"
value="1000"
/>
PPFD
</label>
</p>
<p>
<label>
<input
id="ref_height"
type="number"
min="1"
max="120"
step="1"
value="12"
/>
Height (inches)
</label>
</p>
</fieldset>
<fieldset>
<legend>Actual values</legend>
<p>
<label>
<input
id="power"
type="range"
min="1"
max="100"
step="1"
value="100"
/>
Power <span id="power_level">100</span>%
</label>
</p>
<p>
<label>
<input
id="height"
type="number"
min="1"
max="120"
step="1"
value="12"
/>
Height (inches)
</label>
</p>
<p>
<label>
<input
id="photoperiod"
type="number"
min="1"
max="24"
step="1"
value="12"
/>
Photoperiod (hours)
</label>
</p>
</fieldset>
<fieldset>
<legend>Estimated values</legend>
<p><output id="est_ppfd">1000</output> PPFD</p>
<p><output id="est_dli">43</output> DLI</p>
</fieldset>
</form>
<footer>
<p>
<small>
This is free software.
<a href="https://pub.pink/~poly/src/dli-est.zip">
</a>
</small>
</p>
</footer>
<script>
const form = document.querySelector("form");
const ref_ppfd = document.querySelector("#ref_ppfd");
const ref_height = document.querySelector("#ref_height");
const power = document.querySelector("#power");
const power_level = document.querySelector("#power_level");
const height = document.querySelector("#height");
const photoperiod = document.querySelector("#photoperiod");
const est_ppfd = document.querySelector("#est_ppfd");
const est_dli = document.querySelector("#est_dli");

function updateEstimates() {
const MICROSECONDS = 3_600 / 1_000_000;
const H = Number(height.value);
const L = Number(photoperiod.value);
const N = Number(ref_height.value);
const P = Number(power.value) / 100;
const PPFD = Math.round(
(Number(ref_ppfd.value) * P) / Math.pow(H / N, 2)
);
const DLI = Math.round(PPFD * L * MICROSECONDS);

est_ppfd.value = PPFD;
est_dli.value = DLI;
power_level.textContent = power.value;
}

power_level.textContent = event.target.value;
});
</script>
</body>
</html>
``````

Copy/paste everything in that grey box into a plain text file (i.e. not a Word document) and save it as `dli.html` (or whatever name just make sure it ends with `.html`). Then open that file in a web browser and you should be good to go. If you want it for your phone you can throw that file on any of the free website hosting services.

3 Likes

@poly
As part of my early business education curriculum in 1973-74 I had to take Intro to Fortran and Cobol. It was a very short lived introduction to computer sciences. I did finish with a business degree with NO emphasis on computer systems and languages,

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They’d be big money skills nowadays as most of the stuff still running them are in finance, the DOD, etc.

I tried computer science in college and dropped out after a couple of semesters but spent almost twenty years as a professional developer . Just starting to pick it back up as a hobby recently.

p.s. sorry for the hijack. Back to cannabis related matters

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you’re fine shes doing good… took her out the solo cup and put her in forever home with FF misted the dome and left her alone looking good. Thank u guys for the info @poly so thats my light that u used in the example. I have it about 18-20" away from seedling what should my light be set on is the 50% good