How to Measure Underwater

Step-by-step instructions to use Photone underwater

Our app can be used under water without any limitations – it just needs a bit of preparation and some adjustments. We suggest waterproofing of your device, an eventual calibration, and some recommended settings.

Waterproofing

The obvious necessity is to prepare your smartphone or tablet and eventual diffuser (only required for iOS devices) for its submerged usage. Even though most modern smartphones are water-proof or at least water-resistant, we recommend putting your device including the attached diffuser in a clear plastic bag. In order to get all the air out, submerge most of the bag and then zip it up.

Zip the bag (mostly) submerged to get all the air out. Putting the smartphone in a clear bag ensures that our whole setup is waterproof and ready to be used.

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You can now use Photone as an underwater PAR meter.

Light Source Selection

Selecting the correct light source is crucial for accurate PPFD measurement. Most aquarium lights are weighted heavily on the blue side of the spectrum with LED lights being the most common of them nowadays. Therefore, the LED Blue / White setting most likely is the correct one if you're using LEDs.

For accurate PPFD measurements, make sure to select the correct light source

Touch Screen Adaptations

Depending on your device and bag used, your touch screen might be recognizing random touches under water and thus malfunctioning. This means that the app cannot be operated underwater and it might behave weirdly as touches are recognized. To combat this issue, we highly recommend using our Pro settings. These allow you to disable the hold mode which mostly solves the touch screen issues, whereas enabling the advanced readings allows for a simplified readout of the measurements.

The Pro Settings we recommend to enable for underwater usage

Optional: Calibration

Depending on the kind of plastic bag used, some light will eventually be blocked and therefore require calibration to counteract the loss in transmission. Check if the measurements change significantly with and without a bag under a bright light source.

If the values deviate by more than a few percent, a calibration is recommended. This requires you to take a reference measurement without the plastic bag that you'll then use within the calibration flow. It is absolutely crucial to have a reproducible and stable light setup that is bright enough (i.e. over 10 µmol/m²/s).

As for the calibration itself, we'll use the "Light- / PAR-Meter" option and input our initial measurement as the reference meter's measurement:

The three steps steps to calibrate for the plastic bag in front of the camera

After the calibration is done, you've successfully compensated for the plastic bag's transmission loss and should measure exactly the same with the bag as without the bag before.

Underwater Accuracy

Photone is almost as accurate underwater as it is in air. We compared Photone on various iOS and Android devices and measured median deviations of less than 3% when compared to our high-end reference equipment.

The results showing the deviation of Photone compared to our Apogee reference sensor underwater

If you want to learn more about the accuracy of Photone underwater, we recommend reading through the detailed test we published on our blog.

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