In May 1927, history was made when Charles Lindbergh completed the first transatlantic flight. Piloting the Spirit of St. Louis, Linderlbergh departed from Long Island, New York and arrived in Paris, France, 14 hours and 25 minutes later.
The aircraft’s simple cockpit was fitted with a handful of gauges and controls and no lighting. Since then, considerable progress has been made in airplane cockpit design and illumination. A typical jet is now fitted with a myriad of illuminated symbols, controls, display screens, and both interior and exterior lighting.
The instrument panel and fuel manifold of the Ryan NYP N-X-211 Spirit of St. Louis. (Photo: © Donald A. Hall Photograph & Document Collection)
Backlit signs and symbols are considered a key component of aviation safety. They are also a commonplace fixture in automobiles, signs in public spaces, illuminated computer keyboards, medical equipment and for industrial control panels, among other applications.
Examples of backlit symbol applications, top row left to right: device controls and keypads, instrument panels and avionics, computer keyboards; middle row: automobile dashboards (left), controls (center), and LED-backlit light strips and shapes (right); bottom row left to right: vehicle mirror blind spot indicators, airplane safety symbols, illuminated signs. Image Credit: Radiant Vision Systems
In the aviation and automotive industries, backlighting is generally used to highlight important buttons and controls, and illuminated symbols offer key information to the operator, such as warning lights.
In industries that are heavily regulated, precise specifications for the appearance of various backlit elements are crucial. Illuminated elements must adhere to the stringent demands for brightness (luminance), color (chromaticity), clarity, and shape to make sure they are visible and legible 24/7 to the pilot or driver in all ambient lighting conditions.
Modern pilots rely on an array of backlit indicators and controls alongside various displays in the cockpit of a Boeing passenger jet. Image Credit: Radiant Vision Systems
Quality Issues with Backlit Symbols and Signs
Backlit symbols are generally made by inserting a layer (such as an opaque film) in front of a light source (such as an LED array). The top layer is stenciled, for instance, with laser cutting to form icons, letters, and shapes.
If there are any defects present in the resulting symbols, this may result in errors in the cut out — such as an element missing (exclusion), an extra element (inclusion), misshapen elements, or symbols in the wrong orientation or location (rotated). Manufacturers must carefully inspect backlit panels to amend any such errors.
No driver looks forward to seeing these backlit symbols (low oil, check engine) while driving, but we can all be grateful for a clear early warning to prevent vehicle damage or breakdown. Image Credit: Radiant Vision Systems
To meet safety requirements, manufacturers of backlit panels and films must also adhere to strict light and color tolerances across each region of a panel or sign. During manufacturing, this means testing for any unevenness in the backlight as observed through the overlay.
Quality issues may occur as a result of the lighting array — such as LED luminance values that are not emitting the required brightness, inconsistent color across a sign or inconsistencies from symbol to symbol.
Inspection to Meet Regulatory Standards
Radiant’s light and color measurement systems can be utilized to offer assurances where uniformity in backlit signs and films is key such as those used for public signage, aerospace cabins, directional and information panels, and appliance controls.
Radiant’s VIP™ (Vision Inspection Pack) license with TrueTest™ software offers a combination of photometric measurement capabilities with defect detection to determine inclusions, exclusions, and other symbol integrity issues.
Radiant’s imaging technology has the capacity to test multiple areas simultaneously, rapidly capturing and processing data much more consistently than a human inspector or a spot measurement device.
Examples of inclusion and exclusion defects, as detected by Radiant’s VIP™ (Vision Inspection Pack) software. Image Credit: Radiant Vision Systems
Used with a ProMetric® I Imaging Colorimeter, VIP allows users to measure the average luminance of each colored region, color uniformity in each region, minimum and maximum luminance points, and dominant wavelengths.
Thus, manufacturers are able to offer some guarantee of the visibility and legibility of illuminated icons, text, and shapes, with precise measurements of luminance and chromaticity and identifying nonuniformity in backlit buttons, switches, symbols, indicators, and light strips.
A single image capture in VIP software includes responsive symbol registration, unlimited user-defined POI (points of interest) for photometric measurement (luminance, chromaticity, and more), and automatic defect detection of inclusions, exclusions, and other shape deformations. Image Credit: Radiant Vision Systems
Machine Vision + Photometric Capabilities = A Complete Solution
With VIP, Radiant delivers the first all-inclusive solution for backlit symbol inspection, which performs simultaneous photometric measurements of light and color alongside machine vision-based registration and defect detection.
Combining these capabilities in a single system, VIP significantly enhances the efficiency of measurement for both product development labs and for production-line inspection. VIP aids manufacturers and helps them meet component quality and performance standards outlined in guidelines for various industries, from automotive to aerospace.
Taking advantage of machine vision software functionality, the VIP solution leverages Radiant’s TrueTest™ photometric analyses for luminance (cd/m2), chromaticity (CIE xy, u’v’), and other values within the specific registration areas of complex shapes, including icons, text, and other backlit components.
VIP aids manufacturers in ensuring that trained measurement regions are not hindered by inclusions or exclusions due to inaccurate laser etch or errors in overlays, filters, or other substrate layers.
Users can set pass/fail tolerances for photometric and colorimetric values measured within VIP registrations regions, including specific POI. In this example, the four POI on the Side Lights indicator (right) are shown plotted on the CIE color space (left) based on their chromaticity (xy) coordinates. A user-defined ellipse on the CIE color space sets the chromaticity tolerances for pass/fail based on measured POI color coordinates. Image Credit: Radiant Vision Systems
In high-throughput inspection applications, VIP offers an effective solution for high-speed registration of several different symbols and shapes caught within a single measurement image, applying trained registration regions quickly to numerous components that were inspected in series.
Registration regions can be applied on a global basis (across multiple symbols) to ensure the accuracy of relative symbol locations, sizes, orientations, and aspect ratios; or locally (symbol by symbol) to register each symbol dynamically for measurement and detection of any defects.
VIP locates and registers symbols automatically in new orientations (as components move or rotate) while preserving the same relative placement of custom-POI within each registration region.
VIP saves POI locations for each registration region, ensuring consistent measurement of each icon or shape (such as this airline "fasten seatbelt" icon) even if components move or rotate. Image Credit: Radiant Vision Systems
The capabilities of this dynamic registration ensure that all symbols in a series of components are measured consistently based on the same POI locations, without requiring users to maintain precise fixturing tolerances or reapply registration regions or POI for each measurable component.
To learn more about backlit symbol inspection considerations in the automotive industry and how photometry and machine vision capabilities combine to solve previously complex visual inspection challenges, read the article “Machine Vision and Photometry Inspect Automotive Symbols,” published in Vision Spectra magazine.
This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.
For more information on this source, please visit Radiant Vision Systems.