Objective colour measurement with the spectrophotometer
Colour measurement is a vitally important aspect of coating and paint. What your see is not what you get when lighting, coating effects, and our own perception will change how a colour appears. However subjective our own colour perception may be, there is no denying the power of appearance. A lack of colour matching across products or colour harmony across surfaces is attributed to poor quality and workmanship, and so, there is great value in ensuring a cohesive and coherent colour application. The spectrophotometer quantitatively measures colour as a function of wavelength under controlled circumstances, allowing for an objective measure. But is that all it does?
In this article we look at the latest innovations and updates to the spectrophotometer and what these mean for your workplace. We also look at some of the top spectrophotometers from manufacturers and companies available in the UK
The three ways spectrophotometers measure colour
A spectrophotometer measures the reflection or transmission properties of a material as a function of wavelength. It commonly uses the CIE L*a*b* colour space where L* is the lightness value, and a* and b* are the colour values, representing green-red and blue-yellow colour components respectively. By calculating the change in L*, a* and b* values and determining the overall difference (delta E*), it can be shown how far removed from a colour standard a sample is. Visit our colour measurement explainer for more information on colour measurement and how it works.
Multi-angle, 45°/0° and spherical spectrophotometers
There are three main types of spectrophotometer used in retail, commercial, and industrial applications in coatings and paint. They are named for on the angle of illumination used to assess colour and the angle of detection/viewing angle or the illumination method. These types are:
- Traditional 45°/0° spectrophotometers – In these instruments the angle of illumination is 45°, and 0° is the viewing angle. The detector receives the reflected light at a 0° angle, perpendicular to the sample. These single-angle instruments work well for solid colours.
- Spherical/sphere spectrophotometers (also diffuse/8°) – The sample being measured is illuminated from all directions, and the detector receives the light at an 8° angle from the sample’s surface. The sphere is internal to the machine, providing the reflection and source of the light. These are best for specular or highly reflective surfaces, and users have the choice of including or excluding the gloss component of the surface.
- Multi-angle (MA) spectrophotometers – Primary illumination is at a 45° angle, through it can also be provided at a 15° angle. These are particularly suited for industrial production and special effect surfaces like the metallic and pearlescent finishes in the automotive industry. They are complex to use and are commonly used in labs, production lines, quality control, and shipping areas.
The features that set apart the spectrophotometer
As with so many gadgets nowadays, coating and paint instruments are becoming more and more multifunctional and user friendly. They are designed to easily integrate with a busy working day and deliver accurate and reliable colour data, wherever you may be. Some of the features that come with the modern spectrophotometer are:
- Large, easy-to-read display – A high resolution LCD display will make your job that much easier in all lighting conditions.
- WiFi and USB connectivity – With so much information stored and recorded through the device, it is important to have a variety of connectivity options for wired or wireless operation.
- Data analysis software and pass/fail reference storage – Each manufacturer will provide their own software with their spectrophotometer. As well as all the ease of wireless connectivity, many devices will store thousands of reference standards, allowing a pass/fail result on colour testing.
- Texture and gloss capability – Measure accurately whether the surface is reflective or uneven.
- Variable view size – Switch between aperture sizes to allow testing on large or small scale samples.
What digital standards mean for colour measurement
Inter-instrument accuracy for colour measurement is vitally important to ensure consistent and true readings and measurements across your entire global supply chain. Traditionally, a paint manufacturer will produce master panels to send to producers and it is these panels that provide the working standards for their instrumental control. This system is by no means perfect; there may be inter-instrumental differences, or operator variations that lead to these working standards being different. Which is why a digital standard is so important.
A digital standard for colour measurement only works where there is excellent inter-instrumental accuracy and agreement. This allows one binding reference to be distributed digitally and eliminate the sources of error associated with physical standards. Differences between plants are minimised, ensuring a smooth and seamless workflow throughout the entire supply chain.
Product comparison – a look at the top spectrophotometers
Below we have a look at the features and benefits of three spectrophotometers from top manufacturers. If you are in the market for a spectrophotometer and would like advice or want to be connected to the right manufacturer for your needs, get in touch! Our experts are here to help. Just click the “Request a Quote” button beneath this article and let us know you requirements.
Konica Minolta CM-M6: Perfect for pearlescents and metallics
The Konica Minolta Multi-Angle Spectrophotometer CM-M6 is specifically designed for colour evaluation and measurement of metallic and pearlescent paints on automotive exteriors. It has a ‘double path’ illumination system with 45° illumination and 6 viewing angles (-15°/15°/25°/45°/75°/110° aspecular) providing accurate results, even for curved surfaces. Other features include:
- Variable view measurement area: Ø12mm/Ø6mm
- High resolution 3.5 inch colour LCD display that is easy to read under low ambient lighting condition
- Wireless and USB communication
- Pass/fail judgement
- Measurement speed: approximately 4.5 seconds
Elcometer 6085 Ci64 Portable Sphere Spectrophotometer: Simultaneous SPIN/SPEX output
A handheld sphere spectrophotometer, the Ci64 is available in 3 models – the Ci64 with 4mm and 8mm measurement apertures, Ci64L with a 14mm measurement aperture for large samples, and the Ci64UV with both tungsten and UV LEd illumination. Each of these models comes with simultaneous SPIN/SPEX (specular-included and specular-excluded) output and correlated gloss measurements. Other features include:
- 4,000 reference samples stored in the device
- Pass/fail mode for up to 1000 standards
- Accurate measurement of reflective or uneven surfaces or materials including optical brightening agents
- Quick colour compare for quality control readings without the need to create tolerances or store data
- High resolution colour LCD screen