There are light meter apps for Android – in fact many of them. The issue with all the light meter apps that we are aware of on the Android platform is the way they measure: All of them seem to use the built-in ambient light sensor that can easily be accessed by any software developer. This seems great at first glance, as the ambient light sensor is directly delivering you the illuminance in Lux that you can then use in your app. However, there is one main flaw: It is dangerously inaccurate. The sensor is mainly used to dim the screen brightness according to the available ambient light, which does not require much accuracy at all.
Please mind that this post was written before our own Photone - Grow Light Meter Android app was available. We therefore didn't have the chance to compare our own app as well. However, we will create an updated version of it in the near future.
PAR Meter App Test
As of the beginning of 2021, there already are three "PAR Meter" apps in the Google Play Store, so we took all of them to a quick test. Please mind that this post was written before our own Photone - Grow Light Meter Android app was available.
We used a dimmable 120W 3000K full spectrum LED quantum board and our $500 Apogee SQ-520 full spectrum quantum sensor as the reference. The phone is a Huawei P40 Lite running Android 10 and the latest version of each app as of April 2021.
All of these apps use the ambient light sensor and then calculate PPFD using conversion factors that can be found with a quick Google search or directly within the app. The PPFD Meter app and Tent Buddy use exactly the same set of conversion factors and can be used interchangeably. The Lux to PPFD sensor app includes a different set of conversion factors where no full spectrum LED setting was present. Therefore these measurements were taken using the sun setting. The Photone measurements were taken for reference on an iPhone 11 running app version 2.4.3 with the full spectrum LED setting. All apps were used as is with no calibration performed to keep this true to a real-world scenario.
What you can see clearly is that the ambient light sensor is peaking somewhere around 900 µmol/m²s which reads 48333 lux before the conversion. So measuring high light levels on this phone model is not possible using this technology.
In our point of view, using the tested Android apps must be done with caution. As they generally measure a bit too much until the maximum is reached, you might be tempted to reduce your light intensity and miss out on your plants' growth potential. It is getting dangerous when you really want to max out your light: As the apps can't measure any higher, you don't know how intense your light really is and you might simply destroy your plants – so take care!
When diving deeper into the usage of the ambient light sensor, it also becomes evident that its accuracy is highly dependent on the phone model that you are using. Some seem to measure acceptably accurate within a given range whereas others are just dangerous to use for anything else but changing the screen brightness. This also leads to the issue that Android light meters might seem trustworthy due to acceptable results on a certain phone model in a certain scenario.
Photone for Android
As you should know by now, simply taking the measurement of the ambient light sensor as-is won't do the trick. Therefore, we are spending a significant amount of our energy on research to achieve accurate measurement results across different light levels and on different phone models. Our Android version is in the making and the Beta version is already available for limited early access.
Beta Version Early Access
If you wish to be amongst the first to try our Android version of the Photone Grow Light Meter, you can join our early access Beta via the Google Play access below: