Performance¶

We are quite satisfied with its performance. Since we conduct our experiments in an illuminated booth and use luminance values above \(40 \frac{\mathrm{cd}}{\mathrm{m}^2}\) the i1 Pro suffices. (It is supposed to be not as accurate with luminance values below \(20 \frac{\mathrm{cd}}{\mathrm{m}^2}\)).

We compared our i1 Pro with an optiCAL from CRS. It showed that the i1 Pro is in fact not very reliable below \(10 \frac{\mathrm{cd}}{\mathrm{m}^2}\), but has excellent performance above. Manufacturer guarantees valid measurement up to \(300 \frac{\mathrm{cd}}{\mathrm{m}^2}\). Our plot shows that measurements are pretty accurate up to \(400 \frac{\mathrm{cd}}{\mathrm{m}^2}\).

Luminance of EIZO GS 320 measured with two photometers.

The second plot shows the difference in percent with the optiCAL as baseline. Apart from a constant offset of about 1% the i1 Pro measures exactly what the optiCAL measures.

Deviation of i1 Pro and optiCAL.

It is safe to say that the i1 Pro does a good job as long as you are mostly concerned with photopic vision.

After a while we noticed that we got quite different results for certain measurements after the i1 Pro was re-calibrated (it has to be calibrated on a white spot before each use (see i1 Pro with calibration plate.)

Offset of i1 Pro after new calibration.

This plot shows 30 times 5 measurements with the i1 Pro of the same monitor color. The difference goes up to \(3 \frac{\mathrm{cd}}{\mathrm{m}^2}\) which is quite substantial.

i1 Pro with calibration plate.

How to Measure Luminance Reflected from a Surface¶

The i1 Pro is not actually meant to do what we wanted it to do. We needed to measure the luminance of a wall that was not self-luminous but reflected a certain amount of light. Our solution was pretty simple. We just built a little box that has an aperture on one side and a whole on the other side through which the photometer measures.

Box with photometer to measure luminance of wall.

We then get a luminance value that we compare to the luminance value we get from measuring the monitor with the i1 Pro in the conventional way (just putting it directly in front of the monitor). Since we adjusted the wall to look exactly like the monitor, we can determine the luminance of the wall this way. Luminance in \(\frac{\mathrm{cd}}{\mathrm{m}^2}\) should be independent of (short) distances.