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I'm trying to create specific colors given the RGB values (please not that the RGB values go from (0-255) RGB LEDs use voltage to turn on and the voltage varies from color to color (The red LED in an RGB LED may turn on at 2.7 Volts while the Blue and Green LED in the same RGB LED will turn on at 3.3volts. I was wondering if any one knows of any LEDs / OLEDs that can use the (0-255) RGB color values

Example of a RGB color I'm trying to create? RGB Image

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closed as off-topic by brhans, Wesley Lee, Voltage Spike, ThreePhaseEel, Dmitry Grigoryev Feb 28 '17 at 17:10

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    \$\begingroup\$ any RGB LED should be able to do that... \$\endgroup\$ – PlasmaHH Feb 27 '17 at 16:37
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    \$\begingroup\$ However hard you try, you're not going to produce a convincing grey LED. It'll just be a dim white. However, if it's part of a bigger RGB display, that's another matter. The human eye sees things in comparison with their surroundings. \$\endgroup\$ – Simon B Feb 27 '17 at 16:52
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    \$\begingroup\$ You mean like, you want a solution to convert 3 bytes into 3 power levels for RGB LEDs? It's far too broad. You can use a MCU to drive a small RGB LED with PWM, or use FETs to control .. say an LED strip, or use addressable LEDs, or use LED drivers that accept analog inputs.. It's quite unclear what you want.. \$\endgroup\$ – Wesley Lee Feb 27 '17 at 17:57
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    \$\begingroup\$ LED brightness varies in proportion to current, not voltage. So you need a 3-channel LED driver (or 3 individual drivers) which you can control through some interface. Whether its 0-255 or 0-100% or 0-1 doesn't matter as you can translate easily between them. That being said, this is a shopping question and therefore off-topic. \$\endgroup\$ – brhans Feb 27 '17 at 18:41
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    \$\begingroup\$ Addressable LEDs take bit values not voltage leves. \$\endgroup\$ – pjc50 Feb 27 '17 at 19:53
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I design LED grow lights for Horticulture Research at the University of Florida. I have analyzed every top end color LED out there. Not just studied, analyzed.

It is important to understand Radiant vs, Luminous Luminescence. Luminous is adjusted for the color perception of the human eye.

The perceived brightness, or luminous efficacy, of light is technically specified by the International Commission on Illumination (CIE). Each wavelength efficacy is related to a wavelength of 555nm (Lime Green).

LEDs are generally spec'ed in Luminous Flux. Luminous Intensity is a whole different thing.

But that's not all, Intensity is often confused with Illuminance and Luminance.

So we have four methods of measuring the amount of light emitting from an LED.

  1. Luminous Flux
  2. Luminous Intensity
  3. Illuminance
  4. Luminance

No one has asked the question what is the difference between these 4 measurement.

But that's not all. I touched on this in the previous answer.

The above 4 measurements relate only to Photometric units of measure.
The three basic units of light measurement are:

  1. Photometric (photometry)
  2. Radiometric (radiometry)
  3. Photonic (quantum)

Radiometry is the study of optical radiation of light, ultraviolet radiation, and infrared radiation. Radiometric is a measurement of the actual flux emitted from the light source.

Photonics measures light as quantum particles called photons. Photons are elementary particles of light which carry light's electromagnetic force. Photons, travel in straight lines at the speed of light, and carry a fixed amount of energy. Photons have two distinguishing characteristics, direction and wavelength. Photons are a quantum measurement of light particle energy measured in the quantity of photons per second. Typically measured with some sort of photon detector which counts the number of photons that hit the detector's surface within a period of time.

Photometry, is about human optical visual response to light (luminous spectral response). Photometric is a measurement of the flux emitted from the light source and then adjusted for its sensitivity to the human eye. Photometric measurements only includes light visible to humans. The human eye is most sensitive to green at a wavelength of 555nm (Lime Green) as determined by the CIE (International Commission on Illumination). This 555nm wavelength is the international photometric standard to which all other wavelengths are compared.

The following is from a paper I am currently writing titled "Understanding LEDs"
I am somewhat confident these number are relevant. I do need to have someone else verify they are correct before I publish.

I created this table for common LED colors
enter image description here

CIE sets the spectral luminous efficacy of the human eye for each wavelength starting a 555nm. The CIE defines photopic vision as 683 lumens/watt at 555 nm.

This I wrote a PHP script to create an SVG image from the table of CIE table of CIE Photopic Luminous Efficacy.
Photopic Luminous Efficacy

This sums it up, almost
measurement of light quantities

Then there are the official SI Units of Measure

SI optical units of measure

THE LED DRIVER

LED voltage means nothing with respect to LED brightness. LEDs are current driven with an LED constant current source.

An LED Driver can accurately adjust the current flowing though the LED.

The numerical value for the RGB colors have to be translated to the LED driver. A typical PWM driver will have at least a 1000 intensity increments.

The Radiant Flux of the LED can be adjusted for Luminosity. You want the LED driver's max current set to the luminous flux for the RGB values of 255,255,255. You can then use PWM to Dim the LED for all other values of 0 - 254.

If you were to use the Luxeon Color C line LEDs the Red and Blue Luminous Flux are about 38 lumens and Green is 97 lm. So the driver's max current for the green LED must be reduced by 255% of the Red and Blue max current.

So if the red and blue were set to run at 500mA max then the Green would be set to 195 mA. Then the PWM RGB ratios are the same for all 3 LEDs.

For the driver below the Red and Blue drivers Riadj would be 6.24 ohm and for Green Riadj would be 2.4 ohm

enter image description here

The LM3414 is a very capable yet simple and inexpensive ($1.00) LED driver.
It has the least part count of any driver and it is a common anode driver where only one wire and ground is required for connecting the LEDs, rather than two wires for each LED.

THE RIGHT LEDs FOR RGB

For RGB you want LEDs designed for flawless color mixing with consistent radiation patterns. If you want the best, go with the LUXEON C Color Line

These are tiny (2mm 0.08") color LED with a very wide viewing angle, Red 162°, Blue and Green 175°. They come with secondary optic lenses.

Do not be fooled by their size. The Color C pictured can take over an Amp. Do not be fooled by the datasheet. You cannot look at just the Luminous Flux, but if you do, look at the binned ones near the bottom of the datasheet.

This table is a comparison of the top color LEDs. At first glance it appears the Color C are not quite as bright as the Rebel and XPE especially the red.

A closer look the forward voltage is lower, which means less watts, less heat. Temperature is the most important characteristic when comparing LEDs

The Color C are spec'd at 85° C the others 25° C, that would add at least 10% to Green Luminous Flux, and 50% more for Red. See Temperature vs. Normalized Output graph in datasheet.

Thermal Resistance. 2.8 vs 8.0. This means thermal management is more effective. 285% better in this case.

The there is the viewing angle and spectral distribution of light. These are the best color LEDs for RGB available.

enter image description here

I took this picture to show how small they are. On the left is a LUXEON SunPlus Royal Blue 450nm for Horticulture which is the same as a Color C except spec'd out in Photosynthetically Active Radiation rather than Lumens.

Luxeon Color C and Rebel ES

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  • \$\begingroup\$ There appears to be a discrepancy: you wrote "very wide viewing angle, Red 162°, Blue and Green 175°", but the table shows the angles being equal for each colour. Looking at the Optical Characteristics table at www.lumileds.com/uploads/571/DS144-pdf, I guess your table here has a transcription error. \$\endgroup\$ – Andrew Morton Feb 27 '17 at 20:17
  • \$\begingroup\$ @AndrewMorton I'm impressed. I noticed that but did not think anyone else would. Glad to see someone is getting something out of this. A lot of time and effort went into learning this. This is some of the most important things about LEDs I have learned over the past couple of years. LED datasheets are deceptive. LEDs are much more complex than they appear. Temperature a is a huge effect on LED performance. Is now fixed. The is why I said: I am somewhat confident these number are relevant. I do need to have someone else verify they are correct before I publish. \$\endgroup\$ – Misunderstood Feb 27 '17 at 21:07

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