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FAQ

FAQ

What is light? How is it reflected by different materials? How to illuminate shiny or matte objects? How do contrast and camera position influence the final result? This page answers frequently asked questions about lighting and illumination technologies for Machine Vision. Further questions on the subject can be asked to the support.
A ring light is an illumination product that contains a circular array of LEDs. In Machine Vision, the circular enclosure normally has a central hole for a camera to be placed.
In Machine Vision and identification applications, ring lights can be used for a plurality of lighting scenarios such as being used for pick and place on end of arm (EoA) applications or looking at barcodes on packaging.
Ring lights can be used in two ways when positioned around a camera’s optical axis. They can be used to create a brightfield by flooding an area with light, but this will only work on relatively matte materials. You can also use a ring light by putting both the light and the camera at a low angle between the target surface and the normal to the surface. This method is useful for highlighting edges, scratches and engraved markings, such as dot peen marked codes on shiny metals.
Any light source can damage your eyes if you stare directly into the light source. However, your natural reaction is to close your eyes or stop looking at the light source once this becomes a bit painful, the same way it is when you look at the sun. For eye safety in lighting, the higher risk comes from the wavelengths, such as UV and IR. Infrared light and UV light can both be invisible or appear much weaker to the human eye than the light source actually is. Laser risk class is seperate from illumination products.
A diffused light is a way to describe a light output. A highly focused light source will have more intensity but less homogeneity over a large area. By diffusing a light, it will scatter the light photons, creating more homogeneity but reducing light intensity.
Infrared (IR) light can be used in some situations to see through materials. This is because the longer wavelengths can pentrate through some materials, such as conveyors belts or opaque bottles. Furthermore, IR lighting can be used to make ink disappear from an image, which is why IR is never used in a logisitcs environment to read codes.
LED lighting can come in many wavelengths, such as red, which will typically have a peak light intensity around 630 nm. Other wavelengths include infrared (880 nm), green (525 nm), cyan (505 nm), blue (470 nm), etc. 

White LEDs are not a single wavelength. They are a mix of many colors and some white LEDs may appear more blueish or more yellowish. This is measured as color temperature. For example, a 2,800 k LED is a warm white and a 6,000 k LED is a cool white.
Specific wavelengths of Machine Vision illumination can be purchased, UV illumination included. The UV wavelengths used for Machine Vision are typically starting around 405 nm and going down to around 365 nm. These products can be used for the inspection of things such as details on bank notes, glue seals and inkjet codes that fluoresce under a certain wavelength.
A ring light is an illumination product that contains a circular array of LEDs. In Machine Vision, the circular enclosure normally has a central hole for a camera to be placed.
Ring lights can be positioned in two ways when positioned around a cameras optical axis. They can be used to create a brightfield by flooding an area with light, but this will only work on relatively matte materials. You can also use a ring light by putting both the light and the camera at a low angle between the target surface and the normal to the surface. This method is useful for highlighting edges, scratches and engraved markings, such as dot peen marked codes on shiny metals.
A telecentric lens is used to eliminate the negative effects of parallax, also known as perspective error. It works by removing the cone of vision produced by a conventional lens by having a non-angular field of view. This means the camera can see the true width of round and thick work-pieces, which is great for measurement applications.
The human eye is only responsive to wavelengths in the region of 400 to 700 nanometers (nm), whereas a camera, which can have various types of sensors, is sensative in a large range of spectral emissions. Some cameras are in monochrome because black and white pictures can be paired with specific illumination wavelengths to highlight different colors in the field of view. Additionally, the image processing of monochrome cameras tends to be faster.
Intelligent lighting is not a type of lighting typically used in Machine Vision. It refers to light with automated mechanical movement integrated into the design, typically used in nightclubs or event venues.
Strobe control is an electrical method for synchronizing the strobe signal of an illumination product with the exposure time of a camera. The strobe controller can also set defined duty cycles when using an illumination product in overdrive strobe mode.
UV fluorescence is when an a material or substance emits light when it absorbs some light radiation. Materials will typically fluoresce under UV illumination, such as an LED light source with a wavelength between 365 nm to 405 nm.
In Machine Vision, there is always a specified area that needs to be illuminated from a certain working distance. For this reason, lighting in a Machine Vision lighting portfolio is measured as Lux. Lux =  Lumen / Square meter (lm/m²). Lumen (lm) is the measure of the total quantity of visible light emitted by a source, measured with the units Joules as luminous energy per unit time. 
IP65 means the product is protected against dust ingress and also protected against splashes of water. This makes the product suitable for use in certain environments where there might be some dust in the air or some water spraying. It is commonly specified by the end customer what is required for their factory or machine.
IP67 means the product is protected against dust ingress and also protected against submersion in water. This makes the product suitable for use in certain environments where there might be some dust in the air or some water. It is commonly specified by the end customer what is required for their factory or machine.
IP69K protection is the highest level of ingress protection according to the standard IEC 60529. The standard states that the product can be subject to high pressure and high temperature water jets whilst also being protected from dust ingress. This standard is most commonly used for components on food grade production lines that undergo regular high pressure cleaning cycles.
Dome lights are very diffused lights that are used to illuminate many different types of materals with a lot of intensity and homogeneity. A dome light works by having LEDs illuminate the internal surface of a very matte white dome shape. This light then reflects down into the field of view of the camera. The dome structure will contain a hole at the top for the camera to be placed.
Like all Machine Vision illumination products, the lifetime of the product depends on the amount of heat at the LED junction. If the product is used in continuous working, wenglor products are designed to stay on for the entire warrenty period as a minimum. The lifetime of a product can be further increased for a very long time if the product is turned on by a strobe signal that is synchronised with the image acquisition.
Lights for Machine Vision and identification applications can strobe faster than your brain can process images. If there is a very high strobe rate, it may appear as if the light is flickering to your eye but the Machine Vision system and image acquisition will be stable. In extreme applications where the lights are taken to the limit there may appear to be some flickering due to the rise time of the LEDs - always read the user manuals to understand the performance characteristics of your product prior to turning it on.
The amount of lights required depends on your application. Depending on where you need the light to come from when illuminating your part may decide on how many lights you need. For example, if you need to create a darkfield by illuminating all the way around a part you many need four bar lights to illuminate from each side. 

Another reason you may need more than one light is for power. If you have an application for line scan, the lights will need to run in continuous working. This means you will need a lot of light intensity focused on a single pixel line. This can be achieved by using multiple bar lights all focused on the same camera pixel line, the additional bar lights will add more intensity.
Lumen is the measure of light coming from the source, this is typically not useful for Machine Vision. The measurement of light intensity across an area may be more useful. For the wenglor ZVZF20x in white, the measured lux can be up to 50 klux peak at 100 mm working distance.
Spot lights are beneficial because they are very easy to integrate into tight spaces. wenglor spot lights have user-friendly features such as a threaded body to further this ease of integraton.
Bar lights provide flexible brightfield or darkfield illumination. In order to obtain the best possible image of an object, the installation position, the number of lights and the angle of incidence are important. The bar lights are a solution for Machine Vision, industrial automation, robotics and identification applications.

Learn more about bar lights
Angle changers are optical diffusers that both increase the beam angle from a light source and add some diffusion.
Red light was the first type of LED Machine Vision lighting that reached the market because the technology was the first to be commercially available.
LEDs are the most efficient and versatile type of illumination product. LEDs have enabled many shapes and sizes of illumination products to be possible for the Machine Vision market. Other technologies are fluorescents, xenon or quartz halogen. LEDs can also be used to run continuously or at a very high strobe rate, which traditional technologies cannot do.
All wenglor illumination technology beginning with the product codes: LBA, LBD, LB9, LBB, LFD, LMx can be dimmed from 100% to 30% using the 0…10 V signal on pin 5 on the M12 5P A-coded connector.
All wenglor illumination technology is powered by 24 V DC power supplies. The required current rating on your power supply depends on the product. This information can be found on the specific product page for each product reference or within the datasheets.
Polarizers can be used by applying a polarizing filter to your light and to the camera. When doing this, please adjust the polarization filter on the camera to cross the polarization planes over each other; this will significantly reduce glare. Be careful when using multiple illuminations as the position of the second or more lights may eliminate the effect of polarization.
RGB lighting is a single light source that can be switched between red, green and blue. Some products can combine all wavelengths to create white light.
RGB lighting is a light source that can be switched between red, green and blue. In some cases, all wavelengths can be combined to create white light.
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