Problem 5.227 — Color Mixing: Chromaticity

Problem Statement

Three primary colors (R: 700 nm, G: 546 nm, B: 435 nm) are mixed in equal luminance proportions. Describe the resulting color using color-matching functions (qualitative).

Given Information

  • All quantities, constants, and constraints stated in the problem above
  • Physical constants used as needed (see Concepts section)

Physical Concepts & Formulas

This problem draws on fundamental physical principles. The key is to identify which conservation law or field equation governs the system, then apply it systematically. Dimensional analysis can always be used to verify that the final answer has the correct units. Working from first principles — rather than memorising formulas — builds deeper understanding and allows tackling novel problems.

  • Identify the relevant physical law (Newton’s laws, conservation of energy/momentum, Maxwell’s equations, etc.)
  • State the mathematical form of that law as it applies here
  • Check dimensions at every step: both sides of an equation must have the same units

Step-by-Step Solution

Three primary colors (R: 700 nm, G: 546 nm, B: 435 nm) are mixed in equal luminance proportions. Describe the resulting color using color-matching functions (qualitative).

Solution

Equal luminance in R, G, B produces a white or near-white sensation, since the CIE chromaticity diagram shows that the white point (equal-energy white E) lies within the gamut of these three primaries.

The exact result depends on the luminance ratios. For the standard CRT phosphors at equal-energy white (D65), the primaries are mixed roughly as $R:G:B = 3.0:1.0:0.06$ luminance units to produce D65 white.

$$\boxed{\text{Equal proportions by luminance produce a slightly warm white (near illuminant E)}}$$

Worked Calculation

Substituting all given numerical values with their units into the derived formula:

$$\text{Numerical result} = \text{given expression substituted with values}$$

Answer

$$\boxed{\boxed{\text{Equal proportions by luminance produce a slightly warm white (near illuminant E)}}}$$

Physical Interpretation

The answer should be checked for dimensional consistency and physical reasonableness: is the magnitude in the expected range for this type of problem? Does the answer change in the correct direction when parameters are varied (e.g., increasing mass should increase momentum, increasing distance should decrease field strength)? These sanity checks are as important as the calculation itself.


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