Basic information:

A standardized apperance is essential for a variety of products. The colour of a product is an important quality criterion and therefore a good reproducibility of the measurement results is necessary.

The comparison with the human eye – is like taste or smell – it is subjective.
Spectrophotometry colour measurement replaces subjective perception with an objective measurement.

To measure colour of an object surface two things are needed:

•  A controlled light source
• A method to measure the spectral characteristics of the remitted light 

Evolution for the best solution:

This is an overview of how instruments have evolved during the last decades, based on the integrated illuminant types of which they have used.

Halogen
The first instruments used incandescent lamps to illuminate the sample.

Xenon
Next generation technique has than implemented gas discharge lamps.

LED (Light Emitting Diodes)
Our newest generation of Spectrophotometer instruments work with LEDs.

Halogen – Incandescent lamp

The first artificial light source famously developed by Edison was the “Incandescent Light Bulb”. Electricity runs through a thin wire, a filament which is heated by the resistance and glows, producing light, but also a lot of heat. The spectrum for colour measurement should ideally be white i.e. the remitted energy equally distributed over the visual range. Incandescent light covers the visual range but radiates mainly red and infrared range.

Advantages and disadvantages:
The main drawback is the short life span and aging. Both can affect absolute accuracy.

Xenon – Gas discharge Lamps 

Gas discharge lamps work by passing electricity through an inert gas such as Xenon – This produces a high powered light with a relative high blue component. The Xenon light has a longer lifespan and is brighter than halogen light. It’s bluish spectrum is also better suited for colour measurement. The drawback is life span is also limited, even though better than halogen. Also the light output will vary slightly from one blitz to the next, so that a monitor is needed. Ultra violet components can only be controlled using filters.

Advantages and disadvantages:
Fluctuating Light output – limited life span – high replacement costs – not very eco friendly – high disposal cost