AccuBin™

The race is on to move LEDs to the forefront of general illumination. Before 2006, solid state LED lighting had not been used for general illumination because of a lack of intensity. But today, solid state LED lamps are increasingly used to replace incandescent lamps in commercial, industrial and residential applications. This movement is gaining momentum because solid state light sources generally last 50-100 times longer than incandescent lamps, consume about 25% of the energy, can operate at lower temperatures with lower risk of fire, and are more rugged than common incandescent and fluorescent lamps. What’s more, LEDs can be produced which deliver light up to the equivalent of 175W incandescent bulbs, with energy efficiency equal to that of fluorescents. The use of proprietary packaging systems such as those inherent in all Lamina light engines manage thermal energy which allows those intensities to be achieved, and along with them the ability to illuminate entire rooms with LEDs.

Along the way, more lighting professionals are getting acquainted with a process used in the manufacture of LED light engines called binning. Just what is binning and why is it relevant?

A definition.
Binning can generally be defined as the process used by manufacturers fabricating with semiconductor materials, to account for inherent inconsistencies in light quality and other characteristics. Binning is used by the manufacturers themselves when purchasing LED wafers, or die, that meet the manufacturer’s own stringent performance standards for electrical, thermal, efficiency and optical characteristics. The careful review of all of these criteria determines which die the manufacturer will incorporate into each lighting system they produce. Binning by luminous intensity may be requested when the end product is to be used as a radiant emitter; sorting by forward voltage will guarantee similar current for parallel strings.

Binning gets creative.
Lamina's proprietary Accubin process is used when finalizing production of LED light engines or emitter modules.  Since optics, phosphor coatings and other processes and components added to the original LED die can change output characteristics, for even one single production batch or part number, LEDs can represent a wide spread in terms of certain parameters. Accubin allows Lamina to sort the LEDs according to criteria such as dominant wavelength; peak wavelength; color rendering index (CRI); forward voltage; economical use of all die or devices in a bin; uniform light output (TLF); color uniformity; and white light CRI, TLF, and Correlated Color Temperature (CCT).

For example, lighting designers may require the LED to deliver a very specific point in the color range.  One Lamina case study comes from Cartier, the renowned French jeweler and watchmaker. Here Cartier's lighting designers wanted to make the jewelry in their cabinets sparkle to its utmost brilliance.  In doing so they not only requested the Lamina SoL™ MR16 LED, but also that the Lamina Accubin process be utilized to deliver only those SoL MR16 LEDs that had a very particular binning number, because it created an exact specified color of white light (which can vary widely) to show the jewelry at its utmost brilliance. Cartier has even gone so far as to enter the Lamina Accubin binning number into the company’s construction specification charter covering display cabinetry built for all new Cartier shops worldwide.

The Lamina AccuBin process allows the sorting of LEDs according to their differing criteria, which can include:
•    Dominant wavelength
•    Peak wavelength
•    Color Rendering Index (CRI)
•    Forward voltage
•    Economical use of all die or devices in a bin
•    Uniform light output (TLF)
•    Color uniformity, and
•    White light CRI, TLF, and Correlated Color Temperature (CCT)

The difference of a single dominant wavelength bin can be noticeable to the human eye. Lighting designers with specific requirements in their LEDs as a component of their lighting systems can specify an AccuBin binning code or binning number. This ensures that the LEDs delivered to them perform with the same characteristics consistently, from light engine to light engine.

Lamina is using also using its AccuBin process to enhance the performance characteristics of its products which consist of diode arrays; those products containing the least amount of LEDs have four, those containing the most may have as many as 40. When the arrays are built, an entire production of LED die is assessed for its attributes, and then an algorithm is developed for selection to produce the combined performance out of the end product. This practice leads to economical efficiencies, since more die from a single production run are utilized and fewer are discarded for undesirable characteristics.

Binning in this manner also allows Lamina's end products to deliver, for example, enhanced color rendering since the arrays combine multiple die representing a wide span of CCT, and those die have been combined using highly selective techniques. For example, a common way to create white light with an LED is to use a blue or ultraviolet light source coated with a yellow phosphor. This results in some blue light passing through, and some of it being absorbed to combine with the yellow to create white light. An inherent problem in this practice, however, when using single LEDs is that the white color and color quality suffers in the process. Lamina’s solution involves using several blue die of slightly differing wavelengths together in a highly compact array. Some or all of the dice in the array are coated with the yellow phosphor, to produce a spectrum of emission patterns depending on the particular blue that is utilized, thereby broadening the color rendering the emitter will deliver.

Lamina's AccuBin process used for dominant wavelength utilizes similar techniques. For example, a large shipment of diodes represents a wide variation of wavelengths for green. An algorithm is used to select the die – an appropriate sampling of the range of wavelength variation – and they are then combined in an array to produce a very tight dominant wavelength that is very consistent from unit to unit. Customers enjoy not only consistency in desired product attributes but also cost efficiencies associated with the ability to utilize all dice from a large shipment.

Binning for the future.
As LEDs make headway into use in the general lighting scheme, the process of binning will be one to watch. Will it go away entirely? Will it become a more important part of the LED manufacturing realm? An educated guess would be, probably a little of both.

Use of LEDs for mass, generalized applications will call for manufacturing techniques that can produce consistency of product in highly efficient ways that may not include binning. But, as lighting designers learn more about the type of performance LEDs can deliver, and their use is tested by fresh and innovative design concepts, Lamina's AccuBin process will take on greater importance as a way to create very specific LED performance characteristics for new and unexpected uses.