Under certain circumstances, there may be an advantage to using coloured light – for example, if ambient lighting in a factory has a strong colour bias, it may make sense to configure the scanner to use a particular colour – and to filter the others. This is perfectly possible, but restricts the scanner's ability to measure objects of any colour.

As an example, welding is a common source of blue light pollution in factories. A welder emits very strong blue and UV light – so clearly in this instance, filtering blue light before it reaches the camera can increase the system's immunity to ambient lighting. In contrast, typical factory lighting contains relatively low levels of blue light – so restricting a 3D scanner to blue light scanning can improve performance. In both cases, the scanner's ability to measure objects which are blue would be affected – as a blue light pattern can be invisible on a blue surface. In addition, such filtering restricts the scanner's ability to operate in sunlight – which is predominantly blue. This is a major issue in many aerospace and manufacturing facilities.

Restricting the colours projected – whether to blue, red or green – limits the flexibility of a scanner, but can occasionally be beneficial. While Quartz scanners can be configured to operate as blue light scanners, red light scanners, or even green light scanners, our preferred approach has been to compensate for the ambient light algorithmically. Phase Vision's Quartz scanners integrate advanced algorithms which are robust to ambient light. This can be supplemented with optical filters if required.

The most obvious challenge to using a single colour light source is that a coloured object absorbs or reflects some colours of light more than others. Shining a red laser onto a white surface will create a very visible line; but on a red surface, that line will become invisible. Blue light has the same issue on blue surfaces, and so on.

The same effect is true of a white light – shine it onto a black absorbent surface, and it is very hard to see that white light. However, on a more typical coloured surface, or even a dark grey surface, the white light will be visible. White light removes (or greatly reduces) the colour dependency of non-contact metrology scanners.

When two beams of light cross, they "interfere" with each other. This is the effect that allows us to create holograms – images that appear to float in thin air. These cannot be created with white light – they can only be created where two beams of exactly the same colour cross.

This is exactly the issue that we face with light generated by LED laser sources. These are relatively "narrow band", and where they reflect from a metal surface, they create speckle effects – strange light patterns which can be mistaken for the surface of the object being measured.

This factor restricts the accuracy of laser and other narrowband (single–color) measurement systems, and is a major driver towards the adoption of white light measurement techniques.

White light is superior to single–colour light in measurement applications as it:

• Allows measurement of any colour of object
• Is not affected by speckle effects which can reduce accuracy

In evaluating measurement products, these factors drive the use of white light. Even where there is no strong need to measure coloured components, the reduced dependence on operator skill is a significant bonus.