Photone - Grow Light Meter

Name: Photone - Grow Light Meter
Rating: 4.6 (4931 reviews)
Author: Lightray Innovation GmbH

Perfectly light your plants!

Free · In‑App Purchases

4.9K Ratings
Age Rating

4+
Years
Category

Utilities
Developer

Lightray Innovation GmbH
Language

EN
+ 8 More
Size

83.9
MB

Turn your iPhone or iPad into a PAR meter. Measure PPFD, DLI, lux, foot-candles, and color temperature (kelvin) to give your plants exactly the light they need. Trusted by millions of growers, Photone is the only accurate plant light meter app. How much light do your plants really get? Are your lamps hung too high, dimmed too low, or on for too long? Whether you grow houseplants or use a grow tent, greenhouse, hydroponics system, or aquarium, Photone answers these questions and more. Photone is more than just a PAR meter: it gives you the tools and guidance to understand the numbers. MEASUREMENTS ⎷ Photosynthetically Active Radiation (PAR) as PPFD in µmol/m²/s ⎷ Daily Light Integral (DLI) in mol/m²/d ⎷ Illuminance in lux or foot-candles ⎷ Correlated color temperature (CCT) in kelvin * ⎷ Extended PAR (ePAR) including far-red light (ePPFD, eDLI) * FEATURES ⎷ Industry-leading accuracy ⎷ Heatmaps — Create PAR maps, PPFD maps, DLI maps, lux maps, and export them as images or PDFs ⎷ Logging — Track measurements over time as an interactive chart, Auto-Log sessions, and export or import them ⎷ Projected DLI — Get the daily light your plants receive instantly by entering how long your lamps are on ← perfect for grow lights ⎷ Actual DLI — Leave your device in place and use Auto-Log to sum up the light throughout the day ← perfect when measuring sunlight ⎷ In-app guides ⎷ Light calculators and recommendations ⎷ Excellent low light sensitivity to detect light pollution for plants ⎷ Custom calibration option to align readings to another meter ⎷ No Bluetooth and location permission required ⎷ No ads ⎷ All grow light sources supported (Natural sunlight, LEDs, HPS, MH, etc.) * ⎷ Photone for Apple Watch — monitor live readings from your wrist * ⎷ Average and peak readings * ⎷ Hands-free "read aloud" function * ⎷ Special underwater measurement mode * ⎷ Pro support by real human experts * * These features require an in-app purchase to fully unlock HOW ACCURATE IS PHOTONE? Photone matches the accuracy of professional handheld PAR quantum sensors costing hundreds of dollars. Here's how: ⎷ RAW sensor data — capture true light intensity using the camera, the most precise sensor in your device ⎷ Pre-calibrated per device model ⎷ Developed according to the ISO/CIE 19476 standard for light measurement ⎷ Continuously tested — we regularly calibrate and test on new devices DIFFUSER REQUIRED Like every real light meter, Photone requires a diffuser to measure accurately. A diffuser scatters incoming light evenly on the sensor and prevents hotspots. While it may sound complex, the solution is surprisingly easy. You have two options: 1) Easily build a diffuser yourself in less than a minute using standard printer paper. This is accurate enough for most use cases. 2) Get the dedicated Diffuser Accessory (free worldwide shipping) for best accuracy and convenience. More details on https://lightray.io/diffuser/. (!) Do not rely on apps that do not require a diffuser. They are inaccurate because they ignore the basic physics of light measurement. UPGRADE OPTIONS Photone is free to download and use, with no ads or hidden costs. To unleash its full potential, it offers two types of upgrades: → Lifetime unlocks — one-time purchase, always restorable via your Apple Account → Pro subscription — full access for as long as you subscribe, cancel anytime Photone took 7+ years of R&D to develop. Upgrading unlocks powerful features and keeps the app ad-free for everyone. As a member of 1% for the Planet, we donate at least 1% of all revenue to environmental non-profits — so every purchase helps both your plants and the planet. Terms and Conditions: https://growlightmeter.com/terms/

Ratings & Reviews

4.6

out of 5

4.9K Ratings

Great app, easy to use, from a developer who is fair-minded!
12/28/2025
TeeKayCee
All I needed was something to measure lux, because a sleep expert says we should have lighting measuring less than 30 lux for an hour or two before bed. I tried two other apps first. One was difficult to figure out, and the other one required payment, even though the app description didn’t include that. I took a chance on this app because of the developer’s notes - sounds like a straight-up, fair person. This app was super easy to use; there are instructions on how to make a diffuser by wrapping a strip of printer paper around the front camera. To change the setting to measure in lux, all I had to do was swipe a couple of times. I used it to measure light from various sources to see how it worked, and will be using it tonight to measure my usual evening lighting. I’m moving soon, and after I have my houseplants set up in their new locations, I will definitely upgrade so I can make sure I have optimal lighting for my plants, and to support the app and the developer! There’s so much greed these days especially in children’s apps, so it’s really refreshing to come across someone who is fair-minded like this.

Developer Response
Hi TeeKayCee,Thanks a million for your feedback! It felt like a Christmas present for the whole team 💝🎁 We've put a lot of thought and effort into making the app as easy and user-friendly as possible, and it's amazing to hear that you appreciate that 🤩 We are also keen to design the pricing as fair as possible for every party involved, and it's really good to hear that you appreciate our efforts 🫶 Hopefully, our app helps you sleep, and we wish you good luck with moving 🏡 Fingers crossed that you and your plants like the new place! 🌱🤞 Don't hesitate to reach out to support@growlightmeter.com if questions arise💡All the best,Angela and the Photone team
Great app, easy to use, from a developer who is fair-minded!
12/28/2025
TeeKayCee

All I needed was something to measure lux, because a sleep expert says we should have lighting measuring less than 30 lux for an hour or two before bed. I tried two other apps first. One was difficult to figure out, and the other one required payment, even though the app description didn’t include that. I took a chance on this app because of the developer’s notes - sounds like a straight-up, fair person. This app was super easy to use; there are instructions on how to make a diffuser by wrapping a strip of printer paper around the front camera. To change the setting to measure in lux, all I had to do was swipe a couple of times. I used it to measure light from various sources to see how it worked, and will be using it tonight to measure my usual evening lighting. I’m moving soon, and after I have my houseplants set up in their new locations, I will definitely upgrade so I can make sure I have optimal lighting for my plants, and to support the app and the developer! There’s so much greed these days especially in children’s apps, so it’s really refreshing to come across someone who is fair-minded like this.
Developer Response 12/30/2025
Hi TeeKayCee,Thanks a million for your feedback! It felt like a Christmas present for the whole team 💝🎁 We've put a lot of thought and effort into making the app as easy and user-friendly as possible, and it's amazing to hear that you appreciate that 🤩 We are also keen to design the pricing as fair as possible for every party involved, and it's really good to hear that you appreciate our efforts 🫶 Hopefully, our app helps you sleep, and we wish you good luck with moving 🏡 Fingers crossed that you and your plants like the new place! 🌱🤞 Don't hesitate to reach out to support@growlightmeter.com if questions arise💡All the best,Angela and the Photone team
Useful and user friendly with a very involved attentive developer!
01/21/2020
vitvorg
Best app on the AppStore to estimate PPFD for growing plants. I’m a botanist, and so I know this app won’t replace a $400 par meter, but for quick estimations with your phone? This app is more than worth it. The hold feature is super useful. The background shows a grainy picture that gives you instant feedback that you are aiming your phone correctly, which is a unique feature that even the expensive PAR meters do not have. A suggestion to the developer for a future update would be for the background preview picture to freeze when the hold option is used. The hold option right now freezes the reading which is useful for measuring at actual leaf locations and orientations, but the background picture does not freeze with the reading. It would be amazing for the background image to freeze with the hold measurement, so when you pull your phone back you could see that you were aiming the phone correctly and you could see what you were aiming at when the hold measurement was taken.

Developer Response
Thank you very much for your kind and useful review! We will definitely consider the background image hold for a future release!
Useful and user friendly with a very involved attentive developer!
01/21/2020
vitvorg

Best app on the AppStore to estimate PPFD for growing plants. I’m a botanist, and so I know this app won’t replace a $400 par meter, but for quick estimations with your phone? This app is more than worth it. The hold feature is super useful. The background shows a grainy picture that gives you instant feedback that you are aiming your phone correctly, which is a unique feature that even the expensive PAR meters do not have. A suggestion to the developer for a future update would be for the background preview picture to freeze when the hold option is used. The hold option right now freezes the reading which is useful for measuring at actual leaf locations and orientations, but the background picture does not freeze with the reading. It would be amazing for the background image to freeze with the hold measurement, so when you pull your phone back you could see that you were aiming the phone correctly and you could see what you were aiming at when the hold measurement was taken.
Developer Response 01/21/2020
Thank you very much for your kind and useful review! We will definitely consider the background image hold for a future release!
Useful
Feb 20
Midsantiam
This app is helpful for getting the correct amount of light for my plants. I bought the diffuser and I printed out the lighting chart for autoflowers from their website. I use the dli mode and follow it almost exactly, except I find that 45 dli is a bit much for some plants, so I usually aim for 40-43 dli.If I was going to improve this app, I would add a feature where I could select the type of plant, what week my plants are on, and the number of hours the lights are on, then it could tell me if I need more or less light. In other words, the plant light calculator would be built-in.The upgrade for LED and the diffuser are worth the money, but they should be upfront about it and disclose it before getting the app. I think people would be more willing to pay if they didn’t think they were being misled from the beginning.

Developer Response
Hi Midsantiam, Thanks for your detailed review and your support! It would be interesting to know what phones you tried in your comparison. We factory calibrate for all supported iPhones and with the diffuser accuracy, we can pretty much guarantee that the measurements are within a few percent of each other when used correctly. Android is another story, as our current Beta version works differently and accuracy can't be influenced as much. I'm pretty sure that your iPhone + diffuser accessory would measure close to e.g. an Apogee PAR meter. Please feel free to reach out to our support if you think that isn't the case and would like some troubleshooting help.Best,Dominik & the Photone Team
Useful
Feb 20
Midsantiam

This app is helpful for getting the correct amount of light for my plants. I bought the diffuser and I printed out the lighting chart for autoflowers from their website. I use the dli mode and follow it almost exactly, except I find that 45 dli is a bit much for some plants, so I usually aim for 40-43 dli.If I was going to improve this app, I would add a feature where I could select the type of plant, what week my plants are on, and the number of hours the lights are on, then it could tell me if I need more or less light. In other words, the plant light calculator would be built-in.The upgrade for LED and the diffuser are worth the money, but they should be upfront about it and disclose it before getting the app. I think people would be more willing to pay if they didn’t think they were being misled from the beginning.
Developer Response 12/23/2023
Hi Midsantiam, Thanks for your detailed review and your support! It would be interesting to know what phones you tried in your comparison. We factory calibrate for all supported iPhones and with the diffuser accuracy, we can pretty much guarantee that the measurements are within a few percent of each other when used correctly. Android is another story, as our current Beta version works differently and accuracy can't be influenced as much. I'm pretty sure that your iPhone + diffuser accessory would measure close to e.g. an Apogee PAR meter. Please feel free to reach out to our support if you think that isn't the case and would like some troubleshooting help.Best,Dominik & the Photone Team
Kind of pointless
07/22/2023
Ndustrialhippie
This app caught my attention. I recently installed some grow lights and I simply want to know how far they should be from my plants. Was going to buy a light meter, but then this app says “free” on it. Thought I’d try it out. Well here’s the catch. It’s free to download, but you have to pay for anything actually useful. Theoretically, I’m fine with that. But you have to pay for each individual kind of light. You have to pay for information on what measurements mean. Really? What if, after spending all this money, you find the information is wrong? You can choose to unlock everything for a monthly fee or a onetime fee of $80. But here’s the thing…that same cost will buy a very decent light meter. You can buy a mediocre meter for less than half. And with this app, they insist you make a filter. And seriously, they INSIST. Like the alert will not go away even after you dismiss it, so the warning blocks measurements even after you have done a onetime payment to unlock something. Seriously? I’m just going to buy a light meter without all the hassle, thanks. Recommendation: Save your money and buy a meter instead.

Developer Response
Hi yungstud,Thanks for your detailed inputs 🙏You’re right, Photone is free to download and use. Additionally, there are various upgrades available. For many of our users, the app suffices without any upgrade purchases. If your use case requires an upgrade, you can first try the app, and see that it works and actually fits your needs without any cost. For example, to check how far your lights need to be from your plants you just need the right light source setting which is either free or $6. No matter if and which upgrade you choose, you will always spend way less cash than for a decent handheld PAR meter which comes in at around $600. Even better, Photone offers many more features like DLI, CCT, a plant lighting calculator, in-depth guides, and much more that you won’t get out of a simple handheld meter.As you’ve mentioned, a diffuser is required for accurate absolute measurements. Without it, you could only use the readings to compare them relatively. We’ve made this a bit “pushy” on purpose to prevent users from false measurements. If you're sure you'd want that, you could also disable the detection within the settings.I hope this clears things up a bit 🙂Best,Dominik and the Photone Team
Kind of pointless
07/22/2023
Ndustrialhippie

This app caught my attention. I recently installed some grow lights and I simply want to know how far they should be from my plants. Was going to buy a light meter, but then this app says “free” on it. Thought I’d try it out. Well here’s the catch. It’s free to download, but you have to pay for anything actually useful. Theoretically, I’m fine with that. But you have to pay for each individual kind of light. You have to pay for information on what measurements mean. Really? What if, after spending all this money, you find the information is wrong? You can choose to unlock everything for a monthly fee or a onetime fee of $80. But here’s the thing…that same cost will buy a very decent light meter. You can buy a mediocre meter for less than half. And with this app, they insist you make a filter. And seriously, they INSIST. Like the alert will not go away even after you dismiss it, so the warning blocks measurements even after you have done a onetime payment to unlock something. Seriously? I’m just going to buy a light meter without all the hassle, thanks. Recommendation: Save your money and buy a meter instead.
Developer Response 07/25/2023
Hi yungstud,Thanks for your detailed inputs 🙏You’re right, Photone is free to download and use. Additionally, there are various upgrades available. For many of our users, the app suffices without any upgrade purchases. If your use case requires an upgrade, you can first try the app, and see that it works and actually fits your needs without any cost. For example, to check how far your lights need to be from your plants you just need the right light source setting which is either free or $6. No matter if and which upgrade you choose, you will always spend way less cash than for a decent handheld PAR meter which comes in at around $600. Even better, Photone offers many more features like DLI, CCT, a plant lighting calculator, in-depth guides, and much more that you won’t get out of a simple handheld meter.As you’ve mentioned, a diffuser is required for accurate absolute measurements. Without it, you could only use the readings to compare them relatively. We’ve made this a bit “pushy” on purpose to prevent users from false measurements. If you're sure you'd want that, you could also disable the detection within the settings.I hope this clears things up a bit 🙂Best,Dominik and the Photone Team

Added support for the latest iPhone 18 Pro and Pro Max and added a measurement setup check to the Logging feature to ensure values are comparable.

Version 4.5.3 Sep 30

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Accessibility

Information

Seller: Lightray Innovation GmbH
Size: 83.9 MB
Category: Utilities
Compatibility: Requires iOS 15.0 or later.

iPhone
Requires iOS 15.0 or later.

iPad
Requires iPadOS 15.0 or later.

iPod touch
Requires iOS 15.0 or later.

Apple Watch
Requires watchOS 10 or later.
Languages: English and 8 more

English, French, German, Japanese, Portuguese, Russian, Simplified Chinese, Spanish, Traditional Chinese
Age Rating: 4+

4+

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In-App Purchases: Yes

Photone Pro (Monthly) $5.49

LED Full Spec. lifetime unlock $6.49

Photone Pro (Yearly) $29.49

Sun Lifetime Unlock $5.49

LED (Full Spectrum) Lifetime Unlock $6.49

LED (Red / Blue) Lifetime Unlock $6.49

LED (Full Spectrum + Red) Lifetime $6.49

LED (Blue / White) Lifetime Unlock $6.49

FL (Daylight) Lifetime Unlock $5.49

Photone Pro Lifetime Unlock $97.00

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