Controlling Color Variation in White LEDs

The light emitted from LEDs can vary significantly across the white color spectrum. Colors ranging from “warm” white (yellowish hue) to “cool” white (bluish hue) occur with many variations in between. These ranges are each assigned Correlated Color Temperatures (CCT), measured in Degrees Kelvin. An LED array with different color temperatures mixed together may have profound ef­fects on the quality of the end product. Customers in the LED lighting industry are very critical of such color variations in their products, and this is where the challenge for attaining more uniform color output arises.

LED Manufacturers and Binning 

LED manufacturers control white color variations through the process of “binning”. Binning is the method of sorting and grouping LEDs according to specified parameters, satisfying applications that require tighter color tolerances and less variation between LEDs. For example, one kind of LED will have numerous bin codes that define a more precise color temperature within that LED “family”.

However, the precise outcome of color binning can be lost if companies purchasing from the LED manufacturers fail to keep track or handle the binned LEDs properly. Bin control remains crucial as the LEDs travel up the supply chain to LED solution providers or lighting manufacturers.

Norlux Solution 

At Norlux, the key to building LED arrays with similarly binned LEDs is lot binning control and traceability. Tracking the origin of raw material, especially LEDs, is important to a manufacturer like Norlux. Our team assigns internal part numbers along with a manufacturer’s LED part number in order to differenti­ate the number of LED variants we handle. Every time a new shipment of this particular LED arrives at Norlux, the receiving department will assign a specific internal lot number for that LED. All the LED information is stored under this specific internal lot number. By doing so, Norlux has the ability to trace back all the necessary information related to that LED lot.

Additionally, Norlux also has the capability to measure CCT and chromaticity values with integrating spheres and colorimeters. Data captured from measuring the LEDs’ output can be compared to the LED shipping data provided by the manufacturer and verified for synergy.

Benefits 

By assigning an internal part number and a specific batch number, Norlux is able to manage its white LEDs better when “kitting” the parts for assembly. The possible problem of having LEDs with different part numbers within one product is eliminated because only the specific part number shows in the bill of materials of the prod­uct. In addition, the possibility of releasing the LED with different bin codes is eliminated because each specific internal lot code assigned has the corresponding LED bin code information with the lot code.

If the customer requests a product to be built with a specific bin code, our production planners are able to trace back the bin codes through the internal lot code assigned. Norlux can even mix different internal lot codes as long as the bin codes assigned are the same (even with different manufacturer lot), thus maximizing optimal LED usage.

Conclusion 

By having appropriate control and traceability of white LED products, managing LED bin codes becomes second nature. Having this system in place eliminates the possibility of placing different shades of white LEDs in an array or assembly. This leads to reliable color consistency and ultimately great products that our customers appreciate and rely upon. For more information, please contact Norlux at 630-784-7500 or visit us at www.norluxcorp.com.