ARMOR TILE

TACTILE SYSTEMS

Detectable warning surface light reflection (LRV)

Detectable warning surface light reflection (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.  What matters, is the amount of reflected light off one surface, compared to the amount of reflected light off the adjacent surface. 

Detectable warning surface light reflection or “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 following 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.

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.\

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.

Manny Burgio
Engineered Plastics.

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