The Optimal Kelvin Temperature (CCT) for Marine Applications. ‘Enhancing Forward Visibility in Inclement Weather’

Introduction

Lighting in marine applications plays a critical role in ensuring safety, operational efficiency, and optimal visibility, particularly in challenging weather conditions such as fog, heavy rain, and snow. The selection of an appropriate Correlated Color Temperature (CCT) is a critical factor in optimizing visibility. This draft explores a more ‘scientific’ basis behind selecting an optimal CCT for marine environments, considering human vision, atmospheric scattering, and empirical studies on light penetration through adverse weather conditions.

Understanding Correlated Color Temperature (CCT)

CCT is measured in Kelvin (K) and describes the color appearance of light emitted from a source. General classifications include:

• Yellow white light (<2700K) – Perceived as yellow in color
• Warm white light (2700K–3500K) – Emits a yellowish hue
• Neutral white light (4000K–5000K) – Appears white – think fluorescent tubes
• Cool white light (5000K+–6500K) – May appear to have a slightly bluish tint

Human Vision and Marine Visibility

The human eye’s response to different wavelengths of light varies under different lighting conditions. Scotopic (low-light) and mesopic (intermediate-light) vision mechanisms influence how we perceive contrast and clarity, both important for low light environments:

• Warmer temperatures (2700K–4000K) reduce glare and are better suited for minimizing backscatter in fog and rain.
• Cooler temperatures (5000K–6000K) tend to enhance contrast, making objects appear sharper.
• Daylight white (6000K and above) may however increase scatter and glare, reducing visibility in inclement weather.

*These kelvin temperatures and ranges are not definitive.  

Atmospheric Scattering and Light Penetration

Adverse weather conditions significantly impact how light propagates:

• Fog and Rain: Water droplets scatter shorter wavelengths (blue light – higher CCT) more than longer wavelengths (yellow or red light – lower CCT), causing higher diffusion and reducing effective visibility and the distance at which objects can be clearly seen.
• Snow and Haze: Snow reflects a higher proportion of blue light (higher CCT) making it harder to distinguish objects in front of the vessel; thus, cooler CCT sources can be less effective in contrast enhancement.
• Reflection and Refraction Considerations: In marine environments, most forward-facing lights will experience little to no reflection or refraction, as they operate for the most part, in open-air conditions without intervening surfaces. Unlike urban or automotive lighting applications where reflective surfaces impact light effectiveness, marine lighting must rely solely on direct projection and penetration through varying atmospheric conditions.

Studies suggest that a CCT range of @ 4000K strikes an optimal balance by reducing backscatter while maintaining high contrast and visibility in poor weather conditions.

Variability Among Manufacturers

As earlier noted, not all fixtures at the same given Kelvin temperature will appear identical across different manufacturers. Variations in diode technology, phosphor coatings, and binning processes can lead to noticeable differences in color output and rendering. Even within the same stated CCT range, slight shifts in spectral composition can affect perceived brightness and contrast. This variability underscores the importance of recognizing that different lighting products may contribute a perceptibly different color of light.

Empirical and Industry Studies

A few studies provide some insights into CCT variances and selection for varying operational conditions:

1. Kang, H.-J., & Kwon, S.-J. (2021). “A Study on the Night Visibility Evaluation Method of Color Temperature Convertible Automotive Headlamps Considering Weather Conditions.” Applied Sciences, 11(18), 8661. This study evaluates how different CCTs affect visibility in adverse weather conditions, providing insight into optimal lighting choices.
2. Durmus, D. (2021). “Correlated Color Temperature: Use and Limitations.” Lighting Research & Technology, 54(4), 1477–1493. This paper discusses CCT limitations and perceptual differences in light sources, emphasizing that even identical CCTs can differ significantly due to manufacturing variability.

Recommendations for Marine Lighting Applications

Given the absence of definitive marine-specific research and based on practical guidelines with albeit limited existing literature, a suggested CCT for marine forward visibility in inclement weather is approximately 4000K. This range provides:

• Sufficient contrast for object differentiation
• Minimal backscatter in fog and rain
• Reduced eye strain for operators
• Balanced visibility across various weather conditions

**Note: over the course of 10 years in providing forward (Mast) lighting for Marine and Maritime applications the overwhelming consensus amongst our customers is their preference for a warmer white/ yellowish fixture color (2700K), some even more recently opting for 2200K.  For aft applications a 4000-5000K solution has worked best.

That said, proper luminaire placement, glare-reduction optics, and higher Color Rendering Index (CRI) sources (>80) may further enhance visibility.

Conclusion

Selecting the right CCT for marine lighting requires balancing visibility, contrast, and atmospheric interactions. Although some empirical research supports @ 4000K as the optimal range, it is ultimately dependent on what CCT works best for the operator given their operation, experience and preference.  Further, due to variability in LED manufacturing, it is important to assess specific light sources under real-world conditions and under varying situations to assess what is best for your operation. 

Here is a custom application we did for a smaller vessel in Alaska (480 LED watts) that combines both 2700K and 5000K effectively providing the benefits of both kelvin options into one fixture.  Stay tuned for an upcoming application combining the same kelvin options across (5) fixtures, totaling 3600 LED watts.

References

1. Kang, H.-J., & Kwon, S.-J. (2021). “A Study on the Night Visibility Evaluation Method of Color Temperature Convertible Automotive Headlamps Considering Weather Conditions.” Applied Sciences, 11(18), 8661.
2. Durmus, D. (2021). “Correlated Color Temperature: Use and Limitations.” Lighting Research & Technology, 54(4), 1477–1493.