Automated LED Calibration for Cinema-Stage Light Manufacturers

by Sam Nada | 2021/11/18

Introduction

Cinema LED light manufacturers use what are called “ratio tables” to calibrate their LED lights.  This mostly manual process is time consuming, tedious and prone to errors.  In this article we will introduce automated LED calibration as a way to speed up calibration many times over and ensure precision color accuracy according to CIE 1931 standards.

Topics:

  • Difficulty maintaining color consistency
  • Traditional Calibration using Ratio Tables
  • Automated Calibration of LED lights

Alexander Dummer (unsplash.com)

LED color consistency is difficult for manufacturers

Cinema LED lights are well known for inconsistent colors, even when the lights are the same models from one company.  This is especially problematic with stage performances and cinematic filming, where light quality needs to be consistent and accurate.

Problem with Multi-colored Cinema-Stage LED lights

There are several types of Cinema LED lights, and they are distinguished by the different colored LED chips in each light.

  • 2-color Cinema-Stage LED lights have a warm-light (e.g. 2500K) and a cool-light (e.g. 6500K) LED chips
  • 4-color Cinema-Stage LED lights have R,G,B, W LED chips.
  • 6-color Cinema-Stage LED lights have Red, Green, Blue, Amber, Cyan and Lime LED chips

On each of these lights, the end user can set a desired CCT by adjusting knobs or buttons on the LED light’s panel – in effect the LED light will mix the different colors of LED chips in the light to achieve the desired CCT. However, two separate lights adjusted to the same color (e.g. 5000K) often are quite different when visually compared.

Joshua Hanson (unsplash.com)

The Inconsistency of LED chips and CCT

Manufacturers understand that the problem is the inherent inconsistency in the color for individual LED chips.  LED chips are made from materials that are not always uniform or consistent – that is why LED light colors can only be identified by a “Correlated Color Temperature” range. But it is this “range” that leaves a lot of room for error when trying to achieve consistent color performance between all LED lights.

Lighting manufacturers try to achieve a ±3% discrepancy allowance between all the LED lights they produce, but it is a difficult goal to achieve.

BIN ratings, Gamuts and CCT

Calibrating LED lights with Ratio Tables

Some manufacturers use “ratio tables” to calibrate their lights. They will take a sample LED light and check CCT colors (e.g. 5000K) against a spectrometer.  If there are discrepancies, they will manually adjust (mix) the intensities of the various LED chip colors on the light until arriving at a Color Temperature closer to the Planckian locus.

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These adjustments are recorded into a spreadsheet called a “ratio table” – this ratio table can take up to several hours because it checks many CCT colors. And it takes even longer when you have more LED chip colors (2-color vs 4-color vs 6-color).

The ratio table data will be applied to the firmware of every LED light during production, so that each light will have the data to be able to make their own adjustments.  It’s time consuming and still prone to inaccuracy – so production line quality control still needs to be closely monitored.

Different batches will exacerbate the problem.

It goes without saying that a new batch of LED chips will most likely render the current ratio table useless.  They will have to go through the same process of generating a new ratio table.

Sometimes you don’t know if all LED chips in a shipment are from the same batch, which can further complicate the issue.

MK350S accuracy and precision

Spectrometers are used in manufacturing to validate the light

MK350S accuracy and precision

Ratio tables used to calibrate LED lights.

Automated LED calibration using the UPRtek CG01 Color Genius

The new way to calibrate LED lights during manufacturing is to replace the “ratio tables” with an automated process.  This means that each light on the production line needs to be measured individually, and a set of “personalized” color mixing algorithms need to be applied to each light.

The UPRtek Color Genius system is an Automated LED Calibration system. It captures light data (color and intensities) from an LED light and determines the spectral data for that light.  This data is then made available to the LED light which now has the accurate spectral information to mix the various LED chip colors (e.g. RGBW) to achieve desired end user color temperatures (e.g. 5000K) that are consistent with CIE 1931 standards.

CG01 Color Genius product description
CG01 Color Genius product image

CG01 Color Genius

Every LED light on the factory line will go through this process.  It doesn’t matter that different batches roll through the factory – each light will be calibrated individually by the CG01.

For a factory line, the setup and calibration of a single LED light takes only a few minutes depending on the number of different color LED chips:

  • 2-color LED light: 3 minutes
  • 4-color LED light : 4~5 minutes
  • 5-color LED light : 5~6 minutes
  • 6-color LED light: 6~7 minutes

Additionally, the CG allows simple 2-color LED lights with only two selections (e.g. 2700K &  6500K) to be redesigned to allow for a range of colors selections (e.g. 2700K ~6500K).

 

Automated LED Calibration is the future of Cinema-Stage LED light manufacturing.

In short, the UPRtek Color Genius is essentially replacing the manual ratio table method with an automated LED calibration process. What used to take a full day to make a ratio table for each batch is no longer needed.

When you calibrate all your lights with automatic calibration, you are establishing a baseline from a common source, the CG01 Color Genius System.  So, all lights subsequently calibrated with this product, no matter the batch, will exhibit the same CIE1931 color behavior, right off the production line.

And most important, your customers will get products that are top-tier light quality.  And when they are happy, you are happy.

CG01 Color Genius product image

Color Genius Automated LED Color Calibration

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UPRtek (est. 2010) is a manufacturer of portable, high-precision light measurement instruments; Handheld Spectrometers, PAR meters, Spectroradiometers, Light Calibration Solutions.

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