How to Measure Accurately

Learn what affects the accuracy of the Photone Grow Light Meter

How to Measure Accurately

Prerequisites for an Accurate Measurement

Although we try to design our app as simple and easy to use as possible, there are still a few things that might affect the accuracy of your measurement. This guide explains how you can measure accurately and what you can do if you don't measure what you would expect.

Diffuser Required

For an accurate light intensity measurement, you must use a diffuser. Follow this guide to learn about why and how you can get a diffuser within less than a minute:
Diffuser Required
What is a diffuser, why do I need one, and how do I get one?

Light Source Setting

Make sure you have selected the correct light source setting. This will allow the measurement algorithm to adapt to your light's spectrum. See this guide if you're not sure about which light source you should choose:

Which Light Source to Choose
Selecting the right light source setting is crucial for accurate PAR measurement

Clean Camera

Make sure your camera lens (i.e. the glass covering it) is clean. Even a bit of dust or finger grease can impact the measurement accuracy.

Screen Protector

If you’re using a screen protector, make sure that it doesn't cover the front camera. If it does, it might affect the initial factory calibration and you'd have to recalibrate accordingly. Check the guide below to see what options are available to perform a custom calibration:

How to Calibrate Photone
Short explanations to properly calibrate your device, if needed

Taking an Accurate Measurement

To take a measurement, place your phone or tablet at the top of your plants' canopy and aim it at the light source at a 90° angle. Doing so allows Photone to measure the light that falls on your plants' leaves which is the light, that actually makes them grow. Make sure that you don't interfere with the measurement, by removing your hand or body between the light source and the device.

Place your phone or tablet at the top of your plants' canopy and aim it at the light source at a 90° angle

Additional Tips

Under bright lighting, it may be hard to read the measurement due to the display's reflections or lack of brightness. If that is the case, you can enable the HOLD functionality by touching and holding the lower third of your screen. This freezes the measurement until you release the touch.

As an additional help for your measurements, our Pro Settings allow you to display peak and average readings as well as provide a position indicator to indicate if your device is completely level:

Pro Settings Explained
Learn more about our Pro Settings and how to use them

Not Measuring What You Expect?

Please note that, even though Photone is factory calibrated for every iOS device, some minor differences between devices may occur. A 5-10% difference is to be expected and nothing unusual for almost any light meter. This minor difference won't be noticed by your plants at all. Please mind that even 5% can seem quite high when measuring really bright lights.

If you're comparing the reading of Photone to a cheap illuminance meter or PAR meter, Photone is most likely more accurate. We routinely test common light meters and most of them deviate a lot compared to our professional reference equipment.

Nevertheless, if you have higher trust in your meter or the specifications of your light manufacturer, you can use Photone's calibration option which can be found on the settings page. Read our guide on how to calibrate to learn how to perform your own calibration properly.

Additionally, if you're certain that you followed all the above steps and still aren't measuring what you would expect you can always contact our support team. Make sure to provide us with the required information to troubleshoot your issue, namely:

  • Expected measurement and actual measurement
  • Screenshots (or photos)
  • Type of device (include if you have a screen protector)
  • Type of diffuser that you're using, if any
  • Type of grow light that you're measuring

How to Measure Accurately

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