This app can be very accurate and useful if it's calibrated.

Sensor calibration:

The calibration is a decimal number that corrects the readings of your light sensor on your device multiplied by the amount entered on the "Sensor calibration value" option in Preferences. This decimal number can range from approximately 0.1 up to around 10 depending on the device and it's light sensor.

Calibration procedure:

Use a real light meter, set room lighting level to 100lux (or vary the distance from the light source) according to the real light meter and enter custom calibration values until you match 100lux on the Light Meter's scale. This is a basic calibration procedure.

Sensor linearity:

It is quite possible that the light sensor on your device is not linear, meaning you get measuring errors for very small or very big values of illumination even if you have successfully calibrated it using the procedure described before. In this case inputting a different "Sensor linearity index" can help in situations when your sensor has exponential or logarithmic non-linearity.

With a simpler explanation, inputting sensor linearity index numbers between 0 and 1 fix a situation when your sensor shows higher readings than real on higher illumination. On the other side, inputting numbers between 1 and 2 help in a situation when you get lower reading than real on higher illumination.

Linearity calibration:

Linearity calibration is not a simple procedure because the linearity index is related to and changes the effect of the custom calibration value. So, one using a real light meter must find ideal combination of sensor linearity index and custom calibration value. As a starting point one can use low illumination to set a base custom calibration value and use high illumination to set the sensor linearity index. After this the custom calibration value can be corrected to fix the low reading error that will be a product of this change in the sensor linearity index but after several corrections you can find ideal combination of the custom calibration value and sensor linearity index.

Color calibration:

Some devices equipped with a color light sensor offer a light color temperature measurement. The light color temperature is expressed in degrees Kelvin ('K). The light color temperature calibration can be done using lights with known color temperature (for example some LED lights) using a similar procedure to the calibration procedures described earlier.
By entering different "Color calibration value" you can match the light color readings to match your light and by entering different "Color linearity index" you can correct your readings to be spot-on with different light colors.

Some values for previously calibrated devices are:

HTC Hero (1.22)
HTC Magic (1.33)
HTC Desire (1.23)
HTC Legend (1.41)
HTC Wildfire (1.21)
HTC Wildfire S (1.13)
Samsung Galaxy S (0.75)
Samsung Vibrant (0.71)
Samsung Galaxy Tab (7.52)
Samsung Galaxy S2 (2.15)
Samsung Galaxy Note (0.56)
Samsung Galaxy Beam (1.75)
Samsung Galaxy Golden (1.33)
Samsung Galaxy S3 (1.88)
Samsung Galaxy S4 (7.45)
Samsung Galaxy S6 (1.35)
Samsung Galaxy S6 Edge (1.35)
Samsung Galaxy Note 3 (1.35)
Samsung Galaxy Note 4 (1.35)
Motorola Flipout (0.148)
Motorola Droid Maxx(1.71)
Asus EeePad (1.21)
SE X8i (1.2)
Sony Xperia T (1.17)
LG Nexus 5 (2.15)
LG G3 (1.0)

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