Photone - Grow Light Meter 4+

Perfectly light your plants‪!‬

Lightray Innovation GmbH

    • 4.6 • 2.3K 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 3.2.4

We fixed a problem that may have happened when trying to send us an email. Everything works smoothly again now.

Ratings and Reviews

4.6 out of 5
2.3K Ratings

2.3K 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,

Blackout9642 ,

Amazing app

Only reason I gave 4 stars is due to the fact that this is the only device I have used to measure light output of my full spectrum LED’s. So I’m not entirely sure how accurate its measurements are, or what the standard deviation of the measurements would be. One thing that could be added is a standardized diffuser that would be consistent, it worries me that if I don’t use the exact same thickness and type of paper every-time I may get inaccurate readings. However from the experience I have with the app it works amazingly and seems to give me relatively accurate readouts within a few 1000 Lux or a dozen or so par from what is advertised by the manufacturer of my current light and from what I’ve seen online people using high end spectrometers and other devices get similar data readouts… if your new to growing or just want a general idea… this app is the way to go 1,000%. Will not let you down just take your readings with a grain of salt.

Developer Response ,

Hi Blackout9642,
Thank you for your detailed review and your input! Happy to hear that our app is helpful to you. The deviation between devices is low as we've tested ALL supported iOS devices in our light lab and created specific factory calibrations for them. So as long as you're using the same diffuser, the absolute measurement is comparable between devices. What is introducing a bit of variation (~6% standard deviation in our tests) is the paper diffuser itself due to placement and paper structure. Your input on this is very valuable. You can also reach out to our support if anything else / related comes up.
An update would be greatly appreciated when you've had the chance to test multiple devices :)
Best regards,
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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