Visual inspection in reflected light -
Our assemblies at a glance

Light is a complex subject. For this reason, choosing the right light source is an important factor in the evaluation of colors, as well as the well-being of the employee. 

The human factor is a subjective influence that depends on the visual performance, experience and accuracy of the operator. 

Thanks to our experience in lighting and our specialized products, we can take into account factors such as 

• Fatigue,
• Contrast effect, 
• Color perception and 
• Viewing conditions

positively.

In order to achieve a reproducible and meaningful assessment by the inspector, the selection of the appropriate lighting is crucial.

The light spectrum from approximately 380 to 780 nm, also known as the color spectrum, is the part of the electromagnetic spectrum that is visible to humans.

But: Not all white is the same

The light spectrum is an important criterion for the "quality of light".
Only the spectrum that hits the test object from the light source can be reflected by it and therefore "seen"!

All adjacent spectra have a color temperature of about 5500 K. However, the light spectra are completely different:

Spectrum No. 1:
Here, white light is produced with an RGB LED. With this spectrum of an RGB, it should not be possible to distinguish between different similar hues.

Spectrum No. 2:
This is an LED used in industrial image processing that has a high luminous efficiency. However, the blue peak is unpleasant to the eye and can distort color judgments.

Spectrum No. 3:
With the D65 standard light LED from planistar, however, even subtle color differences can be detected. This applies to both visual inspection and machine vision.
 

Color rendering is a quality characteristic of artificial light compared to natural light. A light source whose light contains all the spectral colors as in sunlight (Ra100) makes the colors of the illuminated objects appear natural.

The Color Rendering Index (CRI) is a benchmark that describes the color rendering quality of light sources.
The Ra value is determined from the average value of the test colors R1 to R8. With the introduction of LED technology, the number of test colors was increased to 14. This is called the Ri value.

The special LEDs in our lights achieve a very high Ri value of about 97, which means that the colors are reproduced as they are in nature and the high blue component typical of LEDs is reduced.

D30 (3000K) is similar to incandescent light and has a pleasant warm tone. Can be an advantage in detecting defects in various materials. 
D40 (4000K) rather rare, but is also used for certain defect detection applications.
D50 (5300K) is widely used in the graphic arts industry and describes the test conditions for colors. It is described in DIN ISO 3664, among others.
D65 (6500K) is used for the visual comparison of colored materials. This is described in DIN EN ISO 3668, among others.

We have based the development of our color control series on these standards.
The specifications of the standards mainly include:

• The light must be similar to daylight with a color temperature of 5000 K or 6500 K.
• The light source must have a color rendering index of Ra>90 (Ra>95 for planistar).
• The surroundings must be a neutral grey, matt color
• For top lighting, illuminance must be approximately 2,000 to max. 4,000 lx

Ideally, the sample is viewed under both light colors. D65 simulates midday, while D50 is more of an evening light because it contains less blue.