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
closed as off-topic by brhans, Wesley Lee, Voltage Spike, ThreePhaseEel, Dmitry Grigoryev Feb 28 '17 at 17:10
This question appears to be off-topic. The users who voted to close gave this specific reason:
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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.
- Luminous Flux
- Luminous Intensity
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:
- Photometric (photometry)
- Radiometric (radiometry)
- 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.
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.
Then there are the official SI 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
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.
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.