Why “Numbers” are different than usual or expected, what can I do?

When using a colour measurement instrument on a daily basis, you will become accustomed to receiving certain “Numbers” or “Results.” As you become familiar with what the “Numbers” should be, you might notice that something has changed and suddenly the “Numbers” are different than expected.

Do not panic. This issue can typically be resolved in a few steps and by checking your measurement conditions and settings.

Take note that your instrument will always measure and report it’s data under the measurement conditions that have been set. It is always returning objective results under those conditions. Often it is not the “Numbers” that have changed, but rather the settings and conditions under which that observation was made.

The importance of measurement conditions and settings on colour measurement.

We have a number of blogs and resources that speaks to the importance of understanding  your measurement conditons and the role settings play in measuring colour.

Colour is a perception of the observation and not a property of the object. Therefore if we change the conditions of the observation, we will receive different results.

Imagine looking at a “White” car in the shining midday sun and compare looking at the same car around sunset. You will notice or might observe that the colour and appearance of the car is different at each time of the day. Has the colour of the car changed, well no, but the conditions under which you observe the car has and therefore the car appears to look different.

Relating this example to colour measurement, if we used a device to measure the car, but for one measurement, we set the illuminant to Daylight and the second we set the illuminant to Fluorescent light, we would receive different L*a*b* results for each measurement. The only way we could compare the two results would be too set the instrument up with identical settings for each measurement.

Settings are important. Know them, understand them and keep them consistent.

What measurement conditions and settings should be checked?

There are about a dozen different measurement conditions that will influence the results. Some of these we can change, while some are inherent in the device and cannot be changed.

For this topic, we only need to focus on the conditions that we can change. Typically, we need to check the following settings:

1. Measurement Type : Reflectance / Transmittance / Petri / Liquid
2. Measurement Area/Aperture : 30mm / 8mm / 3mm
3. Specular Component : Specular Component Included (SCI) / Specular Component Excluded (SCE) / SCI + SCE
4. Illuminant : D65 / C / F11 / A / D50 / …
5. Observer Angle : 2° / 10°
6. Colour Space Used : L*a*b* / L*C*h / Lab / …

Apart from the settings that can be changed on the instrument, it is also important to note sample presentation and procedures.

Check the following as these will influence the conditions of measurement:

1. Are all of the accessories clean and undamaged? Check for any signs of finderprints, residues, chips, scratches etc. What condition are your accessories in compared to when you first received them? Perfect condition or Poor condition?
2. Did you follow the same sample preparation as normal?
3. What environment are you measuring in? Is the temperature consistent?
4. When last did you send your instrument for annual Certification? If your instrument has not been certificated, how can you rely on the results you are receiving?

If you have checked and your settings as well as other conditions are all as they should be but you are still receiving different numbers, then consider the following:

1. The Product or Sample that you are measuring is off-spec and the results you are receiving are accurate. Trust your instrument.
2. Is your instrument performing as you would expect it to? Perform a Health Check on the instrument using a Green Tile to test this.
   Read more about the Green Tile process on this BLOG.
3. Have you considered that there could be damage to the instrument or contamination in the sphere? If you expect this, contact our service department.