Lighting for assembly workstations and visual inspection

The way we perceive things or our environment is influenced by light. This applies to both private and commercial sectors.

Photographers, in particular, work with natural sunlight or their photo studio to highlight landscapes, people, or objects.

With our luminaires, we take on the role of sunlight or the photo studio. We make visible what needs to be seen.

The human factor is a subjective influence that depends on the employee's visual acuity, experience, and precision. Through our expertise in lighting and our specialized products, we can positively counteract factors like fatigue, contrast effects, color perception, and visual conditions.

Visual inspection, often abbreviated as VT (Visual Testing), is an optical or visual non-destructive materials testing method.

While industrial image processing is increasingly being integrated into our industry, a camera ultimately only sees a few pixels, which are analyzed by software based on fixed criteria.

The human eye, on the other hand, is a very precise measuring instrument. It can perceive a multitude of details and assess and evaluate them based on both guidelines and experience. This human component cannot be replaced by software.

Especially in sensitive markets, such as the medical industry, an inspector is used as a second step alongside image processing to evaluate products based on their own judgment.

The fundamental question is whether the inspection process should be conducted in reflected light or transmitted light. The test object and its inspection characteristics are important factors in selecting the appropriate lighting.

Possible inspection characteristics could include:

• Presence
• Completeness
• Damage
• Position
• Surface condition

A description of these should be included in a specification document, which outlines all the characteristics and steps of the visual inspection (non-destructive testing).

It is also important to consider the inspection environment:

• External light, ambient light
• Time constraints for the inspection
• Space conditions before, during, and after the inspection

These and other factors are taken into account by us during the planning and design process to achieve the optimal result.

In direct visual inspection, the inspection point is viewed directly by an inspector. The area to be inspected on the test piece is examined directly with the naked eye. Observation, analysis, and evaluation are carried out by an individual.

In indirect visual inspection, the inspection point is not directly viewed with the eye. The inspection image is captured by a camera and displayed on a monitor. In indirect visual inspection, the image can undergo further processing steps. For instance, the image can be enlarged, details can be optically highlighted for analysis, or the image can be saved for documentation purposes. By transferring the image to a monitor, the evaluation can also be carried out by multiple individuals.

• D30 (3000K) is similar to incandescent light and has a pleasant warm tone. It can be advantageous for defect detection in various materials.
• D40 (4000K) is relatively rare but is also used for specific applications in defect detection.
• D50 (5000K) is commonly used in the graphic industry and describes the testing conditions for colors. It is, among other things, described in DIN ISO 3664.
• D65 (6500K) is used for the visual comparison of color materials. This is also described in DIN EN ISO 3668.

We based the development of our color measuring devices on these standards.

The requirements of the standards mainly include

• The light must correspond to daylight with a color temperature of 3,000, 4,000, 5,000, or 6,500 K.
• The light source must have a color rendering index of Ra > 90 (at planistar, even about > Ri97).
• The surroundings must have a neutral gray, matte color.
• For reflected light, the illuminance must be approximately min. 2,000 to max. 4,000 lx.
• Ideally, the colors to be inspected are assessed under different lighting situations.

Ideally, the sample is viewed under both light colors. D65 simulates a gray midday sky, while D50 mimics evening light, as it contains fewer blue components.