who is in the forest, who is for firewood

When it comes to devices for measuring illumination, many people say “why do you need a device if any smartphone has a luxmeter”.

I tested the accuracy of the light sensors in five smartphones.

The Light Meter application was installed on all smartphones. The readings of smartphones were compared with the readings of the Uprtek MK350D spectrometer and the Radex Lupin luxmeter-pulse meter. At the same time, I checked the results of the BH1750 and TSL2561 sensors connected to the Arduino.

As a light source, I used a Gauss 2020122 lamp with a matte diffuser, controlled via Wi-Fi. The lamp was located above the table, its brightness changed in the application.

The sensors of smartphones and all devices were located at the same point at the same height.

The first measurement was taken with background lighting from a chandelier in the room, the other four measurements were taken at four luminaire brightness levels from minimum to maximum.

As you can see from the table, the results of the BH1750 sensor and the MK350D spectrometer turned out to be quite close, and I think the spectrometer and this sensor give the most accurate results for measuring illumination.

Of the smartphones, the Redmi Note 10 Pro turned out to be the most accurate.

The readings of the built-in light sensor of smartphones are very different, the difference can even be three times.

I tried to add a correction factor, calculating it from the values ​​​​of the illumination measurement of 457 lux. This is what happened (the coefficient in the last column), which is already much closer to the truth, if you do not look at the first column with very low illumination.

Let’s see how many percent the values ​​obtained with the coefficient differ from the readings of the MK350D.

Deviations usually do not exceed 10%, which is not bad at all.

The following conclusions can be drawn:

– You should not use a smartphone as a light meter without a correction factor: the readings may differ from the real ones by a factor of three;

– If you set the coefficient (many applications, including the Light Meter I used, allow this), the smartphone may well measure illumination with acceptable accuracy (5-10%), but an accurate light meter is needed to calculate the coefficient.

© 2022, Alexey Nadezhin

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