Truncated Domes Light Reflection

My topic includes some information which might be helpful in your quest to understand the requirements for truncated domes light reflection values when specifying detectable warning surfaces.  Although I can provide some information herein, I want to be certain that you understand that I am not an expert on all of the requirements of the Americans with Disabilities Act (ADA), the Architectural Barriers Act (ABA), Section 504 of the Rehabilitation Act (1973), California’s Title 24 of the Building Code, the requirements of the California Division of the State Architect, the US Access Board’s Draft Guidelines for Accessible Rights-of-Way, and the Uniform Federal Accessibility Standards.

It is my understanding that when an entity is regulated by more than one set of laws, that the entity must comply with the more stringent of the various segments of both sets of laws.

The California Division of the State Architect, in its Interpretive Ruling Manual, reminds us that The U.S. Access Board develops the minimum design standards for complying with the ADA, and has also developed and considered detailed research studies regarding pedestrians and the use of detectable warning surfaces.  Under the Access Board, the Public Rights-of-Way Access Advisory Committee was established in 1999 to develop additional ADAAG provisions.  The advisory committee reached agreement on recommended accessibility standards for new and altered public rights-of-way covered by the ADA.   Standards proposed by the committee were presented in a report titled Building a True Community.  The draft guidelines issued by the Access Board, consistent with the advisory committee’s recommendations, include revised technical criteria for
detectable warnings.  The U.S. Department of Transportation (USDOT) is a designated agency responsible for enforcing the standards and implementing regulations of the ADA Title II (State and Local Government Services).  The Federal Highway Administration (FHWA), under the USDOT, is the enforcement authority for overseeing pedestrian discrimination issues under the Title II implementing regulations.  Both FHWA and the Access Board are encouraging the use of the new technical criteria for detectable warnings over the original ADA design standard.

The US Access Board’s Draft Guidelines for Accessible Rights-of-Way, in section 1108.1.3, references a requirement for detectable warnings to contrast visually with the adjoining surfaces, either light-on-dark or dark-on-light.

The Code of Federal Regulations, 28CFR, Part 36, covering Nondiscrimination on the Basis of Disability by Public Accommodations and in Commercial Facilities, lists the ADA Standards for Accessible Design.  Section 4.29.2, Detectable Warnings on Walking
Surfaces, states that the detectable warnings shall contrast visually with adjoining surfaces, either light-on-dark, or dark-on-light., and that the material used to provide contrast shall be an integral part of the walking surface.

California’s Building Code, Title 24, Chapter 11A, Division II, Section 1117A.4.7 referring to exterior routes of travel with regard to housing accessibility: a requirement is referenced for detectable warnings, for contrast visually with the adjoining surfaces, either light-on-dark or dark-on-light, and that warning surfaces shall be of the color yellow conforming to Federal Color No. 33538.  Where the color value contrast between the yellow warning and the main walking surface is less that 70%, a 1-inch wide black strip shall separate the yellow warning from the main walking surface.

California’s Building Code, Title 24, Chapter 11B, Division II, Section 1127B.5.8 referring to exterior routes of travel with regard to accessibility to public buildings, public accommodations, commercial buildings and publicly funded housing:  a requirement is referenced for detectable warnings, for contrast visually with the adjoining surfaces, either light-on-dark or dark-on-light, with a requirement for the material used to provide contrast being an integral part of the walking surface (painted or coated surfaces are not acceptable).

California’s Building Code, Title 24, Chapter 11B, Division III, Section 1133B.8.3 referring to transit boarding platforms: a requirement is referenced for detectable warnings, for contrast visually with the adjoining surfaces, either light-on-dark or dark-on-light, with a requirement for the material used to provide contrast being an integral part of the walking surface (painted or coated surfaces are not acceptable).  Also, warning surfaces shall be of the color yellow conforming to Federal Color No. 33538.  Where the color value contrast between the yellow warning and the main walking surface is less that 70%, a 1-inch wide black strip shall separate the yellow warning from the main walking surface.

Armor-Tile does not have published values for truncated dome Light Reflectance Value, because LRV is a relative term.  By that, I mean that the amount of light measured reflecting off any surface varies with the intensity of the light falling on the surface.  Light reflecting off an Armor-Tile or concrete or any other surface, will be different at sunrise, at mid-morning, at high noon, etc.  It will vary with changing atmospheric conditions as well.  What matters, is the amount of reflected light off one surface, compared to the amount of reflected light off the adjacent surface.  With regard to how contrast is measured, I have summarized for you, my understanding of the issue:

“Light Reflectance Value” (LRV) is a relative term used to describe how well a surface reflects light.  Contrast is calculated in percent between the foreground color and the background color.  The current recommendation for detectable warning surfaces is a contrast of at least 70%.

Contrast is determined by the formula:

Contrast=[(B1-B2)/B1] x 100
where B1= light reflectance value (LRV) of the lighter area
and B2= light reflectance value of the darker area.

As Examples:
Assume the reflected light reading off the Armor-Tile is a LRV of 4200 Lux.
Assume the reflected light reading off the surrounding substrate is a LRV of 2300 Lux.
The delta of 1900 divided by the lighter reading of 4200 = 45% Contrast.

Assume the reflected light reading off the Armor-Tile is a LRV of 900 Lux.
Assume the reflected light reading off the surrounding substrate is a LRV of 3400 Lux.
The delta of 2500 divided by the lighter reading of 3400 = 74% Contrast.

Light readings can be taken with any number of reflectance meters.

Mannix offers their DLM 2000A for approximately $125.

Minolta’s Flash Meter V  is geared for photography, but has the advantage of Lux as well as CandlePower readings, memory functions, and a “difference” feature which yields the delta between a standard reading and multiple (and continuous) subsequent readings.  Additionally, it can be made to show the continuous difference in +/– tenths of an f-stop, which can be read directly as a percentage difference from the standard.  The Minolta Flash Meter V sells for about $380.

Spectra makes a meter which may be considered also.  It sells for about $372

Any meter which is used, must be designed to measure reflected light, not ambient light. 
Ambient light is light which is falling on a subject.  Reflected light from a subject is what is important to measure when calculating reflectivity differences and contrast.

If either the Minolta or the Spectra (or similar) meter shown above were to be used for reflectivity readings, the white spherical dome receptor cover would need to be replaced with one designed for reflectivity readings.  The flat disc below is proper for reflectivity.  The domed disc is for ambient readings.  Domes and discs usually only require ¼ turn to remove and replace

It is important, when taking the light readings, to not interfere with the light falling on the subject.

Since measurement off domed subjects (like truncated domes) may catch a direct reflection of the sun, attention should be paid to minimize such occurrences.  This is similar to trying to photograph a car, yet the camera’s metering system is completely fooled by the brilliant reflection of the sun off the windshield.

Multiple readings should be taken to help eliminate anomalies.

If clouds are passing between the sun and the subject, inconsistent readings will result.

If the part of the meter which contains the sensor can swivel, then the sensor can face the sidewalk, while the user can still read the measurement.  Although a good meter should hold the last reading taken on its display, some meters can take continuous readings.  This would allow the user to see whether the measurement is fairly constant as the meter is moved over the surface, or if it is fluctuating wildly.  A swiveling head, or a sensor which is remote from the meter body, is a huge advantage.  All meters pictured above have this feature.

I hope this article gives you a better insight regarding truncated dome light reflectance values.

-By Mark Heimlich and John A.Heffner

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