Companies that manufacture products ultimately used by consumers — interior trim for cars, vinyl siding for homes, decorative stone for landscaping, interior wall paints, etc. — are often discovering that they need to use precise spectrophotometers to ensure first-time color quality and lotto-lot consistency.
But to be effective, these optical instruments must perform their color measurements accurately, quickly and under some truly demanding shop floor conditions. The instruments need to show acceptable repeatability and reproducibility even within an environment of uneven ambient lighting, high levels of humidity, varying temperatures and even significant shock or vibration. Finally, the instruments also need to be inexpensive enough to yield an acceptable return on investment if they are placed on individual production lines to measure color on a real-time 100% inspection basis.
By leveraging technology that was commercialized for other industries, color instrument manufacturers have invented robust, in-line spectrophotometers for the factory floor that measure colors accurately at a fraction of the cost of older technology. The result is that manufacturers now have the means to obtain reliable online data from a high-speed production line that can be used for lean manufacturing techniques such as statistical process control.
The advent of small, intense, and highly reliable illumination sources based on light-emitting diodes (LEDs) has put solid state illumination at the heart of this new generation of spectrophotometers. Spectro manufacturers typically strive to use D65 standard illumination sources to take their measurements. D65 is the specification of white light that spectrally simulates daylight with a 6500K color temperature. D65 is the standard illumination that is commonly used in the graphics arts, paints, coatings, and other industries in which color matching is critical.
Although the phenomenon of electro-luminescence from a semiconductor was observed in the early 20th century, a major breakthrough occurred in the 1990s when experimenters finally developed a high brightness LED made from indium gallium nitride that produces a high intensity light at the blue end of the electromagnetic spectrum. By coating this LED with YAG phosphors that emit light at longer wavelengths when excited by blue light, engineers were able to produce a “white” light that had output across most of the visible spectrum.
While it has not yet developed a single LED that emits a true D65 illumination, the semiconductor industry has developed sufficient white and chromatic LEDs that the D65 standard can be approximated when they are properly mixed together.