Spectroscopic Correlation Analysis Of M/P Ratio And High Color Rendering Index LED Luminaires

Spectroscopic Correlation Analysis of M/P Ratio and High Color Rendering Index LED Luminaires

By Kevin Rao December 1,2025

The evaluation of spectral distribution in lighting products requires the inclusion of biological effect parameters. The M/P ratio serves as an indicator for measuring the non-visual biological effects of light sources, and its correlation with the Color Rendering Index (CRI) has become a focal point in technical assessments.

Calculation Principle of M/P Ratio

The M/P ratio is defined as the quotient of melanopic lux divided by photopic lux. The calculation is based on the melanopic action function mel(λ) and the photopic function V(λ) defined in the CIE S 026/E:2018 standard. Measuring instruments must comply with the ISO/CIE 19476:2014 standard, requiring a spectral wavelength interval of 1 nm.

The M/P ratio quantifies the potential impact of a light source on melatonin suppression. Industrial lighting standard ANSI/IES TM-18-20 stipulates that the M/P ratio for nighttime work environment lighting should be below 0.6.

                                                                  Provided by Excel tools from the WELL Building Institute.

Spectral Characteristics of High-CRI LEDs

High Color Rendering Index LEDs achieve their performance through multi-band spectral enhancement. A typical CRI 97 LED forms three radiation peaks at approximately 450 nm, 540 nm, and 610 nm. This spectral structure increases the proportion of radiant energy in the 450-480 nm band while enhancing the R9 value.

Test data show that at a correlated color temperature (CCT) of 3000K, when the CRI increases from 80 to 95, the proportion of radiant flux in the 450-480 nm band increases from 12% to 18%. This band corresponds to the sensitive region of the melanopic action function.

                                                                 Screenshot from the WELL Building Institute's Excel tool

Comparative Spectral Parameter Data

*Data Source: IES TM-30-20 testing standard, measurement conditions 25°C ±1°C*

                                                     Screenshot from the WELL Building Institute's Excel tool

Analysis of Engineering Technology Impact

Spectral Design Contradiction
Achieving a high CRI requires a continuous spectral distribution in the 600-700 nm band. Current technology enhances the intensity of the 450 nm blue chip to excite red phosphors, leading to increased short-wavelength blue radiation. Tests indicate that for every 10-point increase in R9 value, the radiant flux at 450 nm increases by approximately 3.2%.

Biological Effect Optimization Scheme
Utilizing violet chip excitation technology can reduce the M/P ratio. Employing a 405 nm violet chip with tri-phosphors can maintain a CRI above 95 while lowering the M/P ratio to 0.48. This technology is already applied in medical lighting scenarios.

Lighting Control Strategy
Intelligent lighting systems dynamically adjust the spectrum based on circadian rhythms. Night mode limits the proportion of 450 nm radiation to below 12%, while supplementing illuminance with 590 nm amber LEDs. This system complies with the WELL Building Standard L03 clause requirements.

Application Scenario Guidelines

Office Lighting Configuration
Daytime work areas use light sources with CRI above 90, with M/P ratios controlled within the 0.55-0.65 range. Conference room lighting features adjustable spectrum modes: presentation mode enhances color rendering performance, while nighttime meeting mode lowers the M/P ratio.

Medical Lighting Solutions
Patient room nighttime lighting employs special light sources with CRI 80 and M/P ratios below 0.4. Surgical lighting distinguishes between general ambient lighting and surgical field lighting, the latter maintaining high color rendering characteristics while ambient lighting uses low M/P ratio sources.

Industrial Lighting Standards
Continuous operation sites implement time-based lighting strategies. The first half of the night uses high-CRI lighting, switching to low M/P ratio mode after midnight. The illuminance maintenance factor remains unchanged, while the spectral power distribution is adjusted according to a set program.

FAQ

M/P Ratio Measurement Method
Use a spectroradiometer to measure the spectral power distribution, calculated according to the CIE 218-2016 standard. For rapid on-site assessment, calibrated blue light hazard testers can be used, with results multiplied by a conversion factor of 0.82.

Product Specification Labeling Requirements
Technical documentation for lighting products should include M/P ratio values for three CCT points: 3000K, 4000K, and 5000K. Test reports must specify the standard used and measurement uncertainty, which should be less than 8%.

Existing System Retrofit Solutions
Without changing the luminaires, installing 475 nm cut-off optical filters can reduce the M/P ratio by 35%-40%. Filter light loss is approximately 12%, requiring a corresponding increase in the base illuminance design value.

Standard Compliance Verification
Medical building lighting requires a 24-hour melatonin rhythm impact assessment report. The report should include MLT-Area value calculations and spectral time-series analysis, complying with Appendix H of GB 50034-2021.

Product Selection Decision Basis
Prioritize compromise solutions with CRI 90-93 and M/P ratios of 0.50-0.55. For special scenarios, use tunable spectrum products with daytime mode CRI >95 and nighttime mode M/P <0.45.

Reference Standards & Literature

CIE S 026/E:2018 Measurement System for Optical Radiation on ipRGC-Influenced Responses

ANSI/IES TM-18-20 Design Guidelines for Circadian Lighting

WELL Building Standard v2 L03 Clause

GB 50034-2021 Standard for Lighting Design of Buildings