LED CCT & Chromaticity Calculator
This LED color-science calculator converts CIE 1931 xy, CIE 1960 uv, and CIE 1976 u′v′ coordinates, estimates correlated color temperature and Duv, and compares white LED chromaticity points.
Use it for engineering estimation, LED bin review, optical system discussion, and early lighting design checks. Accurate LED characterization still requires measured spectral power distribution or calibrated chromaticity data.
Engineering tool
LED CCT & Chromaticity Calculator
Convert CIE xy, CIE 1960 uv, CIE 1976 u′v′, estimate CCT and Duv, and compare LED white points.
CIE 1931 x coordinate.
CIE 1931 y coordinate.
Estimated CCT
6,505 K
Result console
- Estimated CCT
- 6,505K
- White classification
- Cool Daylight
- x
- 0.31270
- y
- 0.32900
- CIE 1960 u
- 0.19783
- CIE 1960 v
- 0.31221
- CIE 1976 u′
- 0.19783
- CIE 1976 v′
- 0.46832
- Estimated Duv
- -0.003173
- Approximation
- Engineering estimate
Approximate color preview
This preview is an approximate screen representation. Actual LED appearance depends on spectrum, luminance, observer adaptation, display calibration and ambient conditions.
Planckian Locus Preview
Lightweight xy plot for orientation only. It is not a calibrated color measurement display.
Method Notes
- McCamy's CCT formula is approximate and most useful near the Planckian locus.
Color preview is an approximate screen representation, not a calibrated LED measurement.
Formula reference
LED CCT and Chromaticity Formulas
Coordinate conversions are exact for valid domains. CCT, blackbody xy, color preview, and Duv are engineering approximations.
n = (x - 0.3320) / (0.1858 - y)CCT = 449n³ + 3525n² + 6823.3n + 5520.33u = 4x / (-2x + 12y + 3)v = 6y / (-2x + 12y + 3)u′ = 4x / (-2x + 12y + 3)v′ = 9y / (-2x + 12y + 3)Δu′v′ = sqrt((u′A - u′B)² + (v′A - v′B)²)Variable definitions
- x, y
- CIE 1931 chromaticity coordinates
- u, v
- CIE 1960 UCS coordinates
- u′, v′
- CIE 1976 chromaticity coordinates
- CCT
- correlated color temperature in kelvin
- Duv
- signed distance from the Planckian locus in CIE 1960 uv space
- Δu′v′
- coordinate-space distance between two CIE 1976 chromaticity points
How to Use This Calculator
- Select a conversion or comparison mode.
- Enter measured or datasheet chromaticity values, or enter CCT for a blackbody estimate.
- Review warnings when the point is far from typical white-light regions.
- Use the visual preview only as a rough screen indication, never as validation data.
Worked Examples
D65 reference white
x = 0.3127 and y = 0.3290 estimate near 6500 K, Daylight, u ≈ 0.1978, v ≈ 0.3122, u′ ≈ 0.1978 and v′ ≈ 0.4683.
Warm white estimate
CCT = 3000 K gives approximate blackbody coordinates x ≈ 0.4366 and y ≈ 0.4042, classified as Warm White.
xy to CIE 1960 uv
D65 xy converts to u ≈ 0.1978 and v ≈ 0.3122 using the exact coordinate transform.
xy to CIE 1976 u′v′
D65 xy converts to u′ ≈ 0.1978 and v′ ≈ 0.4683.
LED comparison
LED A at x = 0.4366, y = 0.4042 is warmer than LED B at x = 0.3127, y = 0.3290. Their CCT difference is substantial.
Engineering Notes
- CCT describes the temperature of the nearest blackbody-like white point.
- CCT does not uniquely describe LED color; two LEDs can share CCT but differ in Duv.
- Duv represents offset from the Planckian locus in a chromaticity space.
- CIE xy, uv, and u′v′ are different coordinate systems.
- CIE 1976 u′v′ is more perceptually uniform than xy, but it is not a complete color model.
- LED color depends on spectrum, phosphor composition, current, temperature, and binning.
- CRI, TM-30, spectral power distribution, and luminous flux cannot be derived from xy and CCT alone.
Common Mistakes
- Treating CCT as a complete description of color.
- Ignoring Duv when comparing LED bins.
- Assuming all 3000 K LEDs look identical.
- Confusing CIE 1960 uv with CIE 1976 u′v′.
- Using CCT formulas for saturated non-white colors.
- Assuming a screen preview matches the real LED.
- Assuming CRI can be calculated from CCT alone.
- Comparing chromaticity without considering luminance or spectrum.
Support reference
FAQ
What is correlated color temperature?
Correlated color temperature, or CCT, describes the nearest blackbody-like white point for a light source and is expressed in kelvin.
What is the difference between CCT and Duv?
CCT describes the warm-to-cool direction of a white point, while Duv estimates offset above or below the Planckian locus.
Can two LEDs have the same CCT but look different?
Yes. Two LEDs can share a similar CCT but have different Duv, spectra, phosphor mixes, CRI, luminance, or binning.
What is the difference between xy, uv and u′v′?
CIE 1931 xy, CIE 1960 uv, and CIE 1976 u′v′ are different chromaticity coordinate systems. The u′v′ system is more perceptually uniform than xy but is not a full color-difference model.
Is McCamy's CCT formula exact?
No. McCamy's formula is an approximation that is most useful near the Planckian locus and should not replace calibrated color measurement.
What does positive Duv mean?
Positive Duv generally indicates a point above the Planckian locus with a greenish tendency, while negative Duv generally indicates a pink or magenta tendency.
Can CRI be calculated from xy coordinates?
No. CRI, TM-30, and spectral quality metrics require spectral power distribution data, not only xy coordinates or CCT.
Why does LED color shift with temperature and current?
LED junction temperature, drive current, phosphor behavior, package optics, and binning can shift chromaticity and luminous output.
Is the on-screen color preview accurate?
No. The preview is a bounded display approximation and depends on monitor calibration, luminance, ambient conditions, and LED spectrum.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
Engineering Guide
Understanding LEDs
Learn LED fundamentals including forward voltage, forward current, wavelength, color, luminous intensity, LED types, packages, current limiting, and thermal design.
14 min · Beginner
Engineering Guide
How to Choose the Right LED
Choose LEDs by application, forward voltage, current, brightness, wavelength, CCT, viewing angle, package, power, thermal behavior, and datasheet limits.
15 min · Intermediate
Engineering Blog
10 Common LED Design Mistakes (and How to Avoid Them)
Avoid LED design mistakes involving current limiting, resistor value, forward-voltage variation, excessive current, resistor power, parallel branches, polarity, brightness, thermal design, and color selection.
14 min · Intermediate
Related Calculators
LED Lumen, Candela & Lux Calculator
AvailableConvert lumens, candela, lux, luminous efficacy, and LED quantity.
RGB LED Resistor Calculator
AvailableCalculate separate red, green, and blue channel resistors and power.
LED Strip Power Calculator
AvailableEstimate LED strip power, supply current, voltage drop, injection spacing, and battery runtime.
High Power LED Thermal Calculator
AvailableCalculate LED junction temperature, heatsink requirement, thermal margin, and safe current.
LED Driver Efficiency Calculator
AvailableCalculate LED driver efficiency, power loss, thermal rise, and supply rating.
LED PWM Dimming Calculator
AvailableCalculate PWM duty cycle, timer settings, gamma correction, and switching limits.
LED Power Calculator
AvailableCalculate LED power, supply power, resistor loss, and total circuit power.
LED Current Calculator
AvailableCalculate LED operating current, resistor voltage drop, and resistor power.
Diode Forward Voltage Calculator
AvailableEstimate diode forward voltage behavior and conduction power.
LED Calculators Category
AvailableBrowse LED calculators for current limiting, power, arrays, RGB lighting, and optical estimates.
Disclaimer
This calculator provides engineering estimates for education and early design review. Accurate LED color characterization requires calibrated chromaticity or spectral power distribution measurements.