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)

For man and machine

A strong distinction must be made as to whether the test pieces are inspected and classified by humans or by a camera. The following factors play an even greater role than in industrial image processing:

  • the light intensity
  • the light colour
  • the light quality
  • the arrangement of the luminaires, and
  • the possibility of adaptation to the person in question

As professionals with many years of experience and our in-house development facility, we take into account all special features. planistar offers you individual and powerful luminaires for visual inspection.

Simply let our team advise or Tel. +49 (0) 9364 8060-0

Why by an inspector and not with the help of image processing?

Visual inspection, often abbreviated as VT (= visual testing), is an optical or visual non-destructive material testing.

Although industrial image processing is finding its way more and more into our industry, in the end the camera only sees a few pixels, which are evaluated with software according to fixed criteria.

The human eye, on the other hand, is a very precise measuring instrument. It can perceive much more and judge and assess according to specifications, but also according to 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 test step alongside image processing to assess the products under his own aspects.

Visual inspection in incident light or transmitted light?

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.

Direct or indirect visual inspection

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 right lighting is what counts

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.

Differentiation between different types of norm light

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.

White is not the same as white

Daylight at noon and in the evening are different and make colors look very different.

Do you have any questions?

We would be pleased to advise you on your visual inspection task. In order to meet your needs, we already offer a large product range as standard. These standard products can easily be adapted to your visual inspection. With us, you don’t have to compromise.

More information and points of contact:

+49 (0) 9364

We will be happy to develop tailor-made solutions for you.

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