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Understanding the lightness of a commercial pool’s interior finish is critical to bather safety.

While many contributing factors exist, requiring a white or light-colored interior finish is the primary and long-established method of ensuring the visibility of a swimmer or bather in distress. This provides the contrast necessary to more easily see a person who needs help.

This principle has gained consensus among both of the industry’s predominant model codes — the International Swimming Pool and Spa Code (ISPSC), and the Model Aquatic Health Code (MAHC). In the 2018 edition of the MAHC, for example, section states:

Floors and walls below the water line shall be white or light pastel in color such that, from the pool deck, a bather is visible on the pool floor and the following items can be identified:

1) Algae growth, debris, or dirt within the pool, and 2) Cracks in the surface finish of the pool, and 3) Tile Marker tiles defined in MAHC

However, current codes do not establish a realistic minimum lightness requirement for commercial pools, nor do they offer standardized test methods or procedures to determine whether a finish is light enough. To that end, this article proposes procedures, test methods and code language to establish a unified lightness requirement, which has already gained a foothold in certain regions of the U.S.

But to understand the rationale and methodology behind these suggestions, it is necessary to have some understanding of the properties of color and lightness, and to know the basic building blocks of the science of colorimetry, which allow us to quantify or measure these properties.

Basics of color and lightness

All color that we perceive has its own distinct appearance based on three main properties:

Hue is what we perceive an object’s color to be (red, orange, green, blue, etc.), or the basic color of a material.

Chroma describes a color’s vividness (the intensity of the pure color itself) or dullness (how close it is to neutral gray).

Light Reflectance Value or L* Value is the lightness or darkness of an object or material, based on the amount of light that it reflects back to our eyes.

For this discussion, the primary characteristic is the Light Reflectance Value.

Light can be reflected from, absorbed into, or refracted by an object or material. We perceive the lightness or darkness of an object or material based primarily on how much light reflects from it back to our eyes. The more light that is absorbed, the less that reflects back to our eye. Lighter-colored materials tend to reflect more light, while darker materials absorb more. The less light we see, the darker our brain perceives the object.

We are primarily concerned with the light that reflects back to our eye, or “light reflectance.” An interior finish that has a higher light reflectance, shows a greater contrast against swimmers and bathers, who have a lower light reflectance. This makes it easier for lifeguards and others around the pool to identify someone in distress. Thus, assessing the light reflectance of a finish is our primary method for measuring a commercial pool’s interior finish for safety.

Wet vs. dry

Dry pool plaster samples
Pebble Technology Intl. Dry pool plaster samples
A comparison of dry and wet plaster samples.
Pebble Technology Intl. A comparison of dry and wet plaster samples.

To determine lightness or establish a more realistic lightness requirement for cementitious finishes for swimming pools, the material should be tested dry and wet. Recently some agencies (Florida Building Code) have begun using wet and dry when determining the lightness of a pool interior finish.

Most non-absorbing materials, such as metals or plastics, do not show a change in color when wet, but micro-porous or semi-permeable materials such as pool interior finishes do absorb water. As water penetrates and adheres or coats the particles and compounds within the material, a greater portion of light gets absorbed and scattered into it. So, with less light reflecting back to our eye, the material is perceived as darker.

This phenomenon is evident in the photos above, showing two identical sets of various colors of pool plaster - one dry, the other soaked in water for 15 minutes (or fully saturated), then towel dried.

Of course, the color of the material itself has not actually changed. Once dried, the wet plaster samples revert back to the same color and have the same light reflectance value as the dry set. But in the real world, the wet samples are a more realistic predicator of a pool finish under water.

So, determining the minimum light reflectance value of a pool finish to establish bather safety should be done by the evaluation of wetted (fully saturated) samples, in addition to dry. Dry samples or mockups serve as a quick and efficient means of establishing an initial pass/fail for the color and texture of pool finishes, to determine whether it meets the construction requirements of a specification, code, health department or

bid proposal.

Wet samples are closer to the actual coloration of the pool finish under water. They can better establish whether the material meets requirements for bather safety.

Unification of color systems

There should not be the significant variations in lightness requirements across the country that exist today.

For commercial pools, unified lightness-level requirements and measurements for the interior finish would allow health departments, engineers and agencies responsible for bather safety to be consistent across the country when accepting or rejecting a finish.

Increasing the confusion, there are currently two color systems used in bid proposals, codes and by agencies across the country. These could help develop a common set of requirements. These systems use different methods to establish lightness values.

Munsell Color System uses ‘Munsell Grey Scale’ to express lightness on a numerical range from 1 to 10 where “absolute black” = 0 and “absolute white” = 10. Measurements are expressed to a single decimal point (ie, 6.5, 7.0, etc.)

The Munsell system relies on eye perception of the designer, engineer, health official or other participant to determine whether the color complies with the appropriate code. But color is perceived differently from person to person, and several factors can restrict or amplify the amount of light our eyes receive, including the lighting and surface texture. This makes the Munsell system more subjective.

CIE (L*a*b*) Color System uses Lightness Value (L* value) to express lightness on a numerical range of 0 to 100 where “absolute black” = 0 (zero) and “absolute white” = 100.

This system is more precise. Here, officials and professionals in the field would use a colorimeter to determine the lightness value of an interior finish, rather than human eye perception. This makes it more repeatable.

Bringing everything together

Current codes, specifications, bid proposals and contracts vary dramatically and, in many cases, conflict with one another. Some require the finish to be either white, light colored, or pastel. Others state that minimum acceptable lightness values range from 65 CIE L*Value (or 6.5 Munsell) to 85 CIE L*Value (or 8.5 Munsell).

I suggest a change to this practice. Based on historical acceptance of interior finishes for commercial pools by health departments across the country, the minimum acceptable dry lightness value is 80 light reflectance value, with the wet equivalence being 50 light reflectance value.

Many interior-finish manufacturers and suppliers now address the lightness issue by testing their products that may be used in commercial pools, and making their test results available to health departments, engineers and government agencies. This helps specifiers determine the acceptability of finishes for commercial usage and the minimum level of lightness required for bather safety, based on a unified system of testing and compliance.

On a governmental level, Florida is the only entity that now specifies minimum lightness values, after adopting language in its Florida Building Code in 2018.

More codes and statutes should set such requirements. I would propose this language:

Suggested Code:

The pool interior finish coating of floors and walls shall be comprised of a white or light-colored cementitious binder component together with a white or light-colored sand/aggregate component. The finish coating shall have a dry Lightness level (CIE L* value) of 80.0 or greater and a wet Light or ‘Luminous’ Reflectance Value (LRV or CIE Y value) of 50.0 or greater as determined by test results provided by the manufacturer or contractor, utilizing testing methodology of ASTM D 4086, ASTM E 1477, ASTM E 1347, and British Standard BS 8493:2008+A1:2010.

Suggested Code Commentary:

The dry Lightness (CIE L value) represents the lightness of a dry interior finish surface sample or mockup as compared on a “gray scale,” where 0 = black and 100 = white.

The wet Luminous Reflectance Value (CIE Y value) more accurately represents the lightness and coloration of the wet interior finish surface that is anticipated and perceived visually in a real-world placement environment. While neither value is the exact representation of the interior finish when submersed in pool water, knowing both values, allows additional insight into the anticipated perceived coloration and aesthetic characteristics of an interior finish when placed in a water submersed environment.

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