Photone - Grow Light Meter 4+

Perfectly light your plants‪!‬

Lightray Innovation GmbH

    • 4.6 • 3.4K Ratings
    • Free
    • Offers In-App Purchases



Take the guesswork out of grow lighting! Measure PAR / PPFD, lux, fc, and kelvin: All within the most accurate light meter app out there.

Setting up your plants' optimal lighting is not easy, if not impossible without a proper PAR / PPFD plant light meter. Calculating your indoor garden's daily light integral (DLI) to match your plants’ needs allows you to optimize your lighting for maximal yield at minimal electricity consumption.

Our Photone grow light meter app measures photosynthetically active radiation (PAR) as PPFD in µmol/m²/s, calculates the daily light integral (DLI) in mol/m²/d, and measures illuminance in foot-candles or Lux. It also allows you to measure light temperature in Kelvin which can help you determine if a light is suitable for fruiting and flowering or for vegetative growth.

Photone is by far the most accurate light meter app for plants and achieves industrial grade accuracy that easily compares to dedicated and very expensive quantum PAR sensors. You can learn more on how we achieve ±5% accuracy compared to research grade laboratory equipment and how to achieve maximum accuracy by yourself in our white paper:

The Photone app also contains useful guiding articles to help you get the most out of your plant lighting. In addition, you can find more informative and educational content on our blog:

Wondering how much light your plants need? The plant lighting calculator on our website helps you to dial in your lighting to your specific plants' needs:

To receive an accurate PAR and thus DLI measurement, you need to select the correct light source that you are measuring. Some common light sources are already available for free while others may need to be purchased additionally. In this way, we are able to fund our development efforts and offer the most accurate light meter app out there without annoying ads.

Our Photone Pro subscription enables you to access all supported light sources, measure light color temperature in kelvin, additional pro features, access additional resources for better results in plant growth, and receive our premium support – and there’s even more to come in the future!

The subscription is auto-renewable and automatically renews unless auto-renew is turned off at least 24 hours before the end of the current period. Your account will be charged for renewal at the price listed within 24 hours prior to the end of the current period. Subscriptions made on iOS devices can be managed and auto-renewal turned off in Account Settings for your Apple ID after purchase. Once purchased, refunds will not be provided for any unused portion of the term. But no need to worry, you may cancel at any time.

You can find our terms of service on our website:

As a proud member of 1% for the Planet we are donating at least one percent of all our revenue to environmental nonprofit organizations. With everything that you purchase from us, you will be giving back!

What’s New

Version 3.5.1

After many years of development, we have achieved an even higher level of measurement accuracy! You can now use the dedicated Lightray Diffuser & Cosine Corrector accessory as an alternative to the paper diffuser. Turn your device into a truly professional light meter. Learn more right within the app. This minor update includes fixes for the iPhone SE (1st generation) and devices running iOS 12.

Ratings and Reviews

4.6 out of 5
3.4K Ratings

3.4K Ratings

vitvorg ,

Useful and user friendly with a very involved attentive developer!

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!

Funmcfunster ,

I put my foot in my mouth.

Originally, I had written a review stating how displeased I was for paying $5 for the Full-Spec LED addon. Then, I decided to see what others had said in their reviews of the app, and found an interesting bit of information that really helped me. I was getting inaccurate PPFD reading (300 directly next to a light source for plant cultivation), and was absolutely baffled by the number I got. However, I noticed multiple people, as well as the developer state that the use of a diffuser (like a tissue) is important in some instances. I just tried this and feel the PAR reading is incredibly more accurate than what I originally thought it to be. My apologies to the developer, and thank you to everyone for bringing useful information to the reviews. I would certainly now recommend this app knowing what I do.

Developer Response ,

Hi Funmcfunster,

Thank you very much for your review! We greatly appreciate your insight and are happy that you get good use of our app!

Best regards,

yungstud ,

Kind of pointless

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 🙂

Dominik and the Photone Team

App Privacy

The developer, Lightray Innovation GmbH, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Linked to You

The following data may be collected but it is not linked to your identity:

  • Usage Data
  • Diagnostics

Privacy practices may vary, for example, based on the features you use or your age. Learn More

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