Lighting Types for Barcode Verification
The right light makes all the difference when it comes to scanning and verifying codes. Verifiers use several different lighting angles. 45-degree angle is the most common lighting angle because it is the standard for label barcode verification. 45 degrees ensures that some light reflects off of the label and goes back to the camera. All camera-based verifiers must include 45-degree lighting in order to grade these regular printed codes. Direct part mark (DPM) code verifiers have the additional lighting options of 30 and 90-degree lighting that makes illuminating symbols on the most challenging of surfaces possible.
Barcode verifiers report on code quality parameters and validate data to comply with the International Organization for Standardization (ISO) code quality guidelines or industry application standards. Each guideline outlines the lighting arrangement that is necessary to achieve the proper illumination of a code. Below is a quick look at the ideal lighting angle for common barcode types.
|Lighting Angle||Barcode Type|
|45-degree||1D and 2D barcodes printed on a flat surface (labels), but can also be used for DPM barcodes|
|30-degree or Dome||DPM barcodes printed on curved or textured parts|
|90-degree||DPM or dot peen codes printed or marked on highly reflective surfaces|
Pictured below is an example of how the same barcode looks completely different when viewed using different lighting. The image on the left shows a symbol laser etched into metal illuminated by 45-degree lighting. The background is dark because the shiny surface reflects the incoming light away, and not up, towards the camera. The marked area is not shiny and is scattering some light, some of which does go up into the camera. On the right, the 90-degree light, which is coming straight down, is reflected back up into the camera; therefore, the shiny background appears light. However, the marked area of the code is not very reflective and therefore looks dark. Note that the image on the left is how this code would look as a non-DPM symbol, with low contrast. The image on the right, on the other hand, appears much brighter and has higher contrast. This was one of the main drivers behind the development of the ISO/IEC TR 29158 AIM DPM grading method.
When working with codes that are directly printed onto the surface of a part or onto a curved surface the addition of 30-degree lighting makes a big difference. DPM code verifiers offer 30Q, 30T, 30S and 90 in addition to 45-degree lighting options. 30Q refers to all four sides illuminated by lights at a 30-degree angle. 30T is lighting from two sides and has two options; it can be light from the top and bottom or light from the left and the right. 30S is light from a single side and so there are four different lighting options.
Two-sided light or 30T, is ideal for curved and/or textured surfaces. The images below are an example of an object with a brushed surface texture. The image on the left shows light shown from the left and the right. On the left, we see the effect of the brushed surface, which reflects some of the light from the left and right lights from “tangential” point on the brush strokes. The image on the right shows light from the top and the bottom. To get the best image the light should be oriented parallel to the brush stroke. When it is parallel, the light reflects away, as it does on a shiny flat surface. The ability to use lighting from two, and not four, sides was another driving factor behind the development of the AIM DPM grading method.