Lighting Makes All the Difference in Collision Work

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Normand Cormier is the North American Classroom Training Manager for Axalta Coating Systems [email protected]. Photo Normand Cormier

Have you ever left home one morning with two black socks only to realize at work that one is navy blue? This is a perfect example of metamerism.

What is metamerism

Metamerism occurs when two colours are identical under one light, but different under another. Our perception of colour depends on the light that illuminates an object and that which is reflected. Daylight offers a full spectrum of light, as seen in a rainbow. The sunlight hits the falling raindrops, which reflect all the colors of the spectrum, from red to purple.

A conventional bulb will produce a warm light that has a lot of red and very little green and blue. Therefore, our perception of the objects observed under this light will make them appear to be redder than when they are exposed to daylight.

When repairing the body of vehicles, sometimes the blended colour needs to be adjusted to match the color of the vehicle. It is important to use the right light to perform the analysis that will identify the shade or shades that need to be corrected during the process. The use of an unsuitable light could complicate this task.

To solve the problem

Fortunately, there are options available to us to avoid this. The use of a spectrophotometer is an excellent solution. It is a precision tool that eliminates the subjectivity of the human eye during analysis. Its sensors observe and measure colour under artificial lighting that faithfully reproduces daylight. If you do not have a spectrophotometer, the use of proper lighting is imperative for colour analysis.

The perceived colour is measured in Kelvin (K). The Kelvin scale is an extension of the Celsius scale. Let’s imagine a black object like a cast iron skillet. By heating it, its colour will change. At low temperatures, it will turn red, then orange and yellow. The temperatures to achieve these shades are considered “hot” on the Kelvin scale. If the temperature increases, it will turn white and then blue. These are the “cold” colours in Kelvin.

This table shows the gradation of colours according to the Kelvin scale which goes from hot to cold. Photo Axalta

Adequate lighting in the workshop

When purchasing an auxiliary lamp for colour analysis, the temperature of the light produced by the device should be about 5600K, which is the “normal daytime” temperature. Some accent lights on the market offer a second, lower intensity, to check for a metamerism problem, as in the example of the incandescent bulb above. Indeed, the temperature of the light at sunrise or sunset is about 3200K. So the colours will look redder than mid-day.

The light of a smartphone is between 7000 and 8000K. This one is too blue to do a proper colour analysis.

As with everything, using the right tool makes all the difference!


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