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How to Measure Accurately

Learn what affects the accuracy of the Photone Grow Light Meter

How to Measure Accurately

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.

How Accurate is Photone?

When used correctly, Photone is accurate down to a few percent of deviation compared to best in class PAR meters and illumance meters. You may read more about accuracy and check out some sample measurements in our white paper.

Prerequisites for an Accurate Measurement

  1. Make sure you have selected the correct light source. This will allow the measurement algorithm to adapt to your light's spectrum.
  2. Use a diffuser as explained within the app. If a diffuser is detected, the orange (!)-sign in the background will disappear. Also make sure to use 80g/m2 or 22 lb standard white multi-purpose printer paper.
  3. Make sure the glass in front of your camera is clean as even a bit of dust or finger grease can alter the measurement.
  4. If you use 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 calibrate accordingly.

Taking an Accurate Measurement

Position the phone at the distance to your light where you want to measure light intensity such as your plant's canopy. Point the front camera directly towards the light source. Make sure that you don't interfere with the measurement, by placing your hand or body too close.

Additional Tips

Photone uses the front camera to take an accurate measurement. Sometimes the camera is unable to expose correctly and the reading will be a bit off. Just cover the camera, i.e. with your finger, for a second or two and then release.

Under bright lighting, it may be hard to read the measurement due to the displays reflections. 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.

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 that can be found on the settings page.

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 iOS device (include if you have a screen protector and diffuser paper)
  • Grow light that you're using

How to Measure Accurately