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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.

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.

Unterscheidung zwischen unterschiedlichen Normlichtarten

D30 (3000K) ist ähnlich dem Glühlampenlicht und ein angenehmer Warmton. Kann bei diversen Materialen ein Vorteil in der Fehlererkennung sein.

D40 (4000K) eher selten, wird aber auch bei bestimmten Anwendungen der Fehlererkennung verwendet.

D50 (5000K)  wird häufig in der grafischen Industrie verwendet und beschreibt die Prüfbedingungen für Farben. Dies wird unter anderem in der DIN ISO 3664 beschrieben.

D65 (6500K) wird dagegen für den visuellen Vergleich farbiger Materialien verwendet. Dies wird unter anderem in der DIN EN ISO 3668 beschrieben.

Wir haben uns bei der Entwicklung unserer colour control Serie an diesen Normen orientiert.

In den Vorgaben der Normen sind hauptsächlich enthalten:

  • Das Licht muss Tageslicht mit einer Farbtemperatur von 3.000K, 4.000K, 5.000K bzw. 6.500K entsprechen
  • Die Lichtquelle muss einen Farbwiedergabeindex von Ra > 90 haben (bei planistar sogar ca. Ra95)
  • Die Umgebung muss eine neutral graue, matte Farbe besitzen
  • Bei Auflicht muss die Beleuchtungsstärke ca. min.2.000 bis max. 4.000 lx betragen.
  • Ideal werden die zu prüfenden Farben unter verschiedenen Lichtsituationen bewertet.

Im Idealfall wird der Prüfling unter beiden Lichtfarben betrachtet. Bei D65 wird ein grau verhangener Himmel um die Mittagszeit simuliert, bei D50 eher ein Abendlicht, da dieser weniger Blau-Anteil enthält.

Weiß ist nicht gleich Weiß

Tageslicht am Mittag und am Abend ist sehr verschieden und lassen Farben unterschiedlich aussehen.

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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