Choosing the illumination which helps users of inspection microscopes achieve the optimal image results depends upon the type of component or part and its details of interest that must be revealed [1-4].

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LED microscope illumination technology provides several advantages for microscopy imaging when compared to halogen lights. These advantages are:

Inspection microscope users can obtain helpful advice from this article when attempting to select optimal illumination for part or component observation. The following information should help users choose the appropriate illumination for microscope inspection.

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Near vertical illumination (NVI) is achieved with LEDs positioned very close to the optical axis. It provides nearly shadow-free lighting and is practical for parts and components with recesses and deep holes or those that require long working distances.

This article gives users of inspection microscopes helpful advice when attempting to select optimal illumination or lighting systems for part or component observation. The illumination used for a microscope has a very important effect on the final image quality and greatly influences the details which are visualized. The following information should help users choose illumination that produce imaging results which are optimized for their inspection needs.

Up until 10 to 20 years ago, halogen lights [5] were the most common type of illumination for inspection microscopes. However, since that time LED (light-emitting diode) lights [6,7] have been more and more utilized for microscope illumination due to the reasons given below.

In addition to the high-quality optics integrated into Leica microscopes, it is important to identify the component details to be analyzed and the field of view (object field) required for observation when selecting an illumination system. It is also worthwhile to consider the advantages of computer encoding of the microscope and the performance of the microscope’s optics, such as objective lenses in terms of transmission, chromatic correction, and planarity, i.e., planapochromatic, achromatic, etc.

Light illuminationNagoya

Users of inspection microscopes may have to try multiple types of illumination in order to find the optimal lighting [10,11].

Guide for choosing the appropriate LED illumination The quick selection guide for the LED3000 and LED5000 series of illumination solutions is shown below in table 2. The LED3000 series is designed for more routine applications (e.g., inspection and QC) and the LED5000 series for more advanced applications (e.g., FA and R&D). This guide can be very helpful for microscope users attempting to find the most appropriate illumination for inspection of particular components or parts.

Coaxial illumination (CXI), where the beam of light is guided through the optics and reflected from the part and component, works best for smooth and reflective components. It is especially useful if fine cracks or surface quality must be assessed.

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The LED illumination solutions are described below. These include the LED3000 and LED5000 systems, mainly used with stereo [9] or digital microscopes [12], which are often exploited for inspection. Examples of other applications they can be used for are failure analysis (FA) and research and development (R&D). Some basic information about the LED3000 and LED5000 systems are shown in table 1.

Images of a metallic coin acquired with various LED illuminations are shown in figure 1. The coin images demonstrate clearly the differences in contrast which can be achieved.

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Finding the right microscope illumination for inspection of components or parts can be challenging at times. However, the advice and recommendations mentioned here can aid users when investigating various illumination solutions in order to find the ones which give optimal results for image observation and recording.

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There are several key factors to consider for high quality microscopic observation and imaging of a component or part when selecting the proper type of illumination:

Multi-contrast illumination (MCI), utilizing repeatable contrast with lighting from 2 different directions and angles, is useful for parts and components with hard-to-find details.

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Example images of various samples are shown below. The images were recorded with a Leica stereo microscope (M60 or M125) equipped with a Flexacam c5 digital microscope camera and a LED3000 or LED5000 illumination system. The types used were a ring light (RL) [with diffusor or polarizers], near vertical (NVI), coaxial (CXI), spotlight (SLI), multi-contrast (MCI), and diffuse (DI) or highly diffuse (HDI) illumination.

Diffuse and highly diffuse illumination (DI and HDI) are designed for reflective, non-flat or curved parts and components. These can be difficult to image due to the amount of back-reflected light.

Inspection of components and parts for industrial manufacturing and production, process engineering, quality control and assurance (QC/QA), failure analysis (FA), or research and development (R&D) often is done with the aid of a microscope. The performance of the microscope used has a significant impact on inspection efficiency.

Spotlight illumination (SLI) with flexible goosenecks offers high contrast lighting suitable for many types of parts and components.

Ring light (RL) gives bright and uniform illumination; suitable for many types of parts and components. Additionally, diffusors and polarized light sets are available for both ring-light types. These accessories reduce the problems of glare and highlighting of spots.