About

This utility is engineered for optical physicists, lighting directors, and color scientists who require more than just a rough approximation of the visible spectrum. Unlike basic color pickers, this tool integrates Planck’s Law of Black Body Radiation and CIE 1931 Color Matching Functions to simulate how physical light properties translate to human perception and sRGB display standards.

Accuracy in spectral visualization is critical in fields ranging from astrophysics (classifying stars by temperature) to architectural lighting (matching CRI and CCT). This application calculates the spectral radiance curve, photon energy, and frequency in real-time. It handles both continuous spectra (thermal radiators) and monochromatic inputs, providing a bridge between the physical world of electromagnetic waves and the digital world of hex codes.

Formulas

To determine the peak wavelength λ_max of a black body radiator at temperature T, we use Wien’s Displacement Law:

λ_max = bT

Where b is Wien's displacement constant, approximately 2.897 × 10^-3 m⋅K.

The energy E of a single photon at a specific wavelength is calculated using the Planck-Einstein relation:

E = h ⋅ cλ

Where h is Planck's constant (4.1357 × 10^-15 eV⋅s) and c is the speed of light.

For the full spectral radiance L, we apply Planck's Law:

L(λ,T) = 2hc²λ⁵ 1e^hcλk_BT − 1

Reference Data

Classification	Source / Illuminant	Temp (K)	Peak (nm)	Photon Energy (eV)
Standard Illuminant	CIE A (Tungsten Filament)	2856	1000+	1.24
Standard Illuminant	CIE D50 (Horizon Light)	5003	580	2.14
Standard Illuminant	CIE D65 (Average Noon Daylight)	6504	450	2.75
Standard Illuminant	CIE F2 (Cool White Fluorescent)	4230	Emission	N/A
Star Class	Class M (Betelgeuse)	3000	966	1.28
Star Class	Class G (The Sun)	5778	501	2.47
Star Class	Class A (Vega)	9600	302	4.10
Star Class	Class O (Zeta Puppis)	40000	72	17.2
Gas Discharge	Sodium Vapor (Low Pressure)	2200	589.3	2.10
Gas Discharge	Mercury Vapor	6800	546.1	2.27
Natural	Blue Hour (Civil Twilight)	10000	475	2.61
Natural	Match Flame	1700	1700+	0.73
Technology	High-CRI LED	4000	450+Phos	Mixed
Technology	CRT Monitor White Point	9300	Variable	Variable

Frequently Asked Questions

The Planckian Locus is the path that the color of an incandescent black body radiator takes in a chromaticity diagram as its temperature changes. It starts from deep red at low temperatures, passes through orange, yellow, white, and finally to blue-white at very high temperatures. This tool visualizes where a specific temperature sits on this spectral path.

Colors outside the visible spectrum (UV < 380nm or IR > 750nm) cannot be displayed on a screen. Additionally, the sRGB color space of monitors is much smaller than the full gamut of human vision. When a calculated color falls outside what your monitor can physically display, we mathematically compress it to the nearest displayable approximation, but mark it as theoretical.

It is an approximation based on the CIE 1931 2-degree Standard Observer. However, "White" is relative. A 3200K light looks white to a camera set to Tungsten balance, but orange to a camera set to Daylight. This tool assumes a standard D65 (Daylight) white point for the display, meaning 6500K will appear pure white, lower values warm, and higher values cool.

Use them as a reference, not a rule. Physical gels (like Rosco or LEE filters) work by subtraction (absorbing wavelengths), whereas screens work by addition (emitting light). While the hue will be similar, the saturation and luminosity behavior in a 3D physical space will differ from a 2D backlit display.

Photon energy is inversely proportional to wavelength. Violet light (shorter wavelength) carries more energy per photon (~3.1 eV) than Red light (~1.7 eV). This is why UV light causes sunburn (high energy breaks chemical bonds) while infrared just feels warm.