Color Temperature and CRI Selector Tool
Analyze and select light sources based on Color Correlated Temperature (CCT) and Color Rendering Index (CRI). Calculates chromaticity coordinates, Duv (distance from blackbody locus), and provides application suitability ratings.
Formulas Used
1. CCT → CIE 1931 Chromaticity (x, y) — Kang et al. (2002):
For 1667 K ≤ T ≤ 4000 K:
xc = −0.2661239×10⁹/T³ − 0.2343580×10⁶/T² + 0.8776956×10³/T + 0.179910
For 4000 K < T ≤ 25000 K:
xc = −3.0258469×10⁹/T³ + 2.1070379×10⁶/T² + 0.2226347×10³/T + 0.240390
yc is computed as a cubic polynomial in xc (coefficients vary by CCT range).
2. CIE 1960 UCS (u, v):
u = 4x / (−2x + 12y + 3)
v = 6y / (−2x + 12y + 3)
3. CIE 1976 UCS (u', v'):
u' = u v' = (3/2)·v
4. Duv (Distance from Planckian Locus):
Duv = v'actual − v'blackbody
Positive Duv → above locus (greenish); Negative Duv → below locus (pinkish).
|Duv| ≤ 0.006 is generally acceptable per ANSI C78.377.
5. Reciprocal Megakelvin (MRD):
MRD = 10⁶ / CCT
6. CRI (Ra):
Ra = (1/8) × Σ Ri (i = 1 to 8), where Ri = 100 − 4.6·ΔEi
(Ra is provided as input; full spectral computation requires SPD data.)
Assumptions & References
- Chromaticity coordinates use the Kang et al. (2002) approximation, valid for 1667–25,000 K (Journal of the Optical Society of Korea, 6(4), 2002).
- CIE 1960 UCS and CIE 1976 UCS transformations follow CIE 015:2018 (Colorimetry, 4th edition).
- Duv is defined per ANSI C78.377-2017; acceptable range is |Duv| ≤ 0.006 for most lighting products.
- CRI (Ra) is defined by CIE 13.3-1995; full calculation requires spectral power distribution (SPD) data — Ra is user-supplied here.
- Application suitability thresholds follow IES Lighting Handbook (10th ed.), EN 12464-1, and ANSI/IES RP-1-20.
- Museum/art gallery recommendation of Ra ≥ 95 follows CIE 157:2004 guidelines.
- Photography/studio standard of 5000–5600 K follows ISO 3664:2009 (viewing conditions for graphic technology).
- CCT range is limited to 1,000–20,000 K for practical lighting applications.
- Duv offset is applied as a vertical shift in CIE 1976 u'v' space (approximation; exact shift follows the locus tangent).