Visual inspection – lighting systems for visual inspection

In addition to solutions for image processing, there is no shortage of test pieces that have to be visually inspected and evaluated by humans. Our LED luminaires are specially adapted to the needs and applications of backlight testing or incident light inspection relating to such manual inspection tasks.

DIN EN 1308:2016 (Non-destructive testing - Visual testing)

The fundamental question to be clarified is whether the test procedure should be carried out in incident light or transmitted light. The test object and the test criteria must be taken into account.

Possible test criteria could be:

• Presence
• Completeness
• Damage
• Position
• Surface texture

For this purpose, a description should be drawn up in a specification sheet in which all characteristics and work steps of the visual inspection (non-destructive test) are listed.

Furthermore, the operating environment must be taken into account:

• Extraneous light, ambient light
• Timing requirements for the inspection
• Space conditions before, during and after the test

These and other factors are taken into account by us during the planning and conception phase in order to achieve an ideal result.

In direct visual inspection, the point to be inspected is examined by an inspector. The test specimen to be examined is inspected directly with the naked eye. Observation, analysis and assessment are carried out by one person.

With indirect visual inspection, the eye does not directly capture the area to be observed. The image to be inspected is captured by a camera and displayed on a monitor. Indirect visual inspection allows the inspection image to be subjected to further work steps. For example, the image can be enlarged, details can be optically highlighted for analysis or the image can be saved for documentation. By transferring the data to a monitor, several persons can also carry out the assessment.

The human factor is a subjective influence that depends on the visual performance, experience and accuracy of the employee. Through our experience in the field of light and our specialised products, we can positively counteract factors such as fatigue, contrast, colour perception and viewing conditions. This selection of a suitable illumination is crucial to achieve a reproducible and meaningful assessment by the inspector.

D30 (3000K) is similar to incandescent light and a pleasant warm tone. Can be an advantage in defects detection for various materials.

D40 (4000K) rather rare, but is also used in certain defects detection application.

D50 (5000K)  is often used in the grafics industry and describes the test conditions for colors. This is described, among other things, in DIN ISO 3664.

D65 (6500K) , on the ohter hand, is used for the visual comparison of colored materials. This is described, among other things, in DIN EN ISO 3668

We developed these color control series based on these standards.

The requirements of the standards mainly include:

• The light must correspond to daylight with a color temperature of 3.000K, 4.000K, 5.000K or 6.500K.
• The light source must have a color rendering index of Ra>90 (for planistar even about Ra 95)
• The environment must have a neutral gray, matt color
• With top lighting, the illuminance must be approx. Min. 2.000 to max. 4.000 lx.
• The colors to be tested are ideally assessed under different lighting situations.

Ideally, the test object is viewed under both light colors. With D65 a gray overcast sky is simulate around noon, with D50 it is more of an evening light because it contains less blue.