Sussex, Wisconsin, USA – Vision inspection systems with actively cooled light-emitting diode (LED) lighting technology are more likely to deliver enhanced inspection image quality at lower operational costs than those using alternative light options, according to a new white paper by researchers at QuadTech, Inc., a global leader in press control technology.

Authors Tim Bergin, John Cusack and Kris DeSmet compared the image representation of foil and paperboard products when illuminated by two sources of LED, tungsten halogen and fluorescent light forms. LED-illuminated images showed both mid-tone gray foil and white overprinted samples appeared smooth and visually accurate. In both cases there was neither compromise in inspection settings nor distortion.

An LED is a semiconductor light source. When it is switched on, electrons recombine with holes within the device, releasing energy in the form of photons. Optical components reflect and shape the radiation pattern, resulting in bright light.

Of the three lighting options, LED was found to have optimum white light output of 6,700 kelvin, resulting in display of true-to-life colors. Furthermore, RGB Color proportions can be adjusted resulting in a white light source with adjustable temperature. LEDs last up to 100,000 hours, compared with 3,000 for fluorescent and under 700 for tungsten halogen.

The paper examines the relationship between LED performance and temperature. The most important aspects of LED light design are stable light intensity and color temperature. Prolonged heat and higher ambient temperature accelerate the degradation rate of the device, resulting in decreased output. For instance, reducing a white LED from 100°C to 45°C boosts output by 25 percent.

Only temperature-controlled LED lighting, achieved with active (liquid) cooling, can create the repeatable conditions to utilize a reusable Golden Template and accurately monitor color algorithms. Active cooling, therefore, ensures stability of light intensity and safeguards against color changes during print runs and from one print run to the next.

LED technology has advanced considerably since it was developed in the early 1960s. Early LEDs emitted only low-intensity red light and were used primarily as indicator lamps for many devices. Today, LED technology cuts across the visible, ultraviolet and infrared wavelengths, and is featured in numerous applications from building lighting to high-definition televisions.

White paper co-author John Cusack, QuadTech Product Manager, comments: "LED lighting for print inspection has far surpassed the performance of other lighting options. Temperature control by actively cooling offers an unmatched ability to maintain consistency, repeatability, life-cycle stability and to maximize product lifespan. This research demonstrates why QuadTech's inspection system has been designed to utilize  LED lighting for stable color output."