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Retroreflective meaning12/6/2023 ![]() ![]() This tells us how much light the sensor is receiving, but 15 m has no real significance other than being a practical distance for lab measurements. Let’s assume that our sensor, positioned at an observation angle of 0.2°, and a rotation angle of 0°, collects 0.00522 lm of light. We use a receiver sensor with a 1 inch (0.0254 m) diameter aperture to measure a spot within the cone of retroreflectivity at a distance of 15 m. Since we cannot test every scenario, we need to instead measure how efficiently the retroreflector sends the available light back in a particular direction. what the driver sees, is contingent on many factors, including headlight intensity, headlight direction, sign location, and more. The reality is that the “brightness” of a retroreflector, i.e. Of course, if our sample was getting more or less light than the scenario depicted, its brightness would change. If the retroreflector is able to return 50% of the energy it collects, a total of about 2 lumens will be sent back out. As a result, it will only collect about 4 lumens (lm) of the light available to it. Our sample has an entrance angle component of -4° in accordance with the spec (which is the same as an entrance angle of 4° since β can only be positive.) This means that our sample is facing slightly away from the light source it is also only 0.5 m 2. The retroreflector, depending on its size (m 2) and orientation will collect a portion of the “light in”. It provides the sample with an illuminance of about 8 lx (lumens/m 2) - this is our “light in”. Let’s assume we have a fixed light source pointed towards a 0.5 m 2 sample. In this case, an entrance angle component of -4°, an observation angle of 0.20°, and rotation angles of 0° and/or 90° (refer to Chapter 5 for a description of each angle.) Observation AngleĪMinimum Coefficient of Retroreflection (R A) cd/fc/ft 2 (cd*lx -1*m -2) We measure how effectively (efficiently) they send light back towards a particular direction. Because retroreflectors do not emit light, we do not measure their brightness. Given the typical measures of “brightness” that we come across for light bulbs, flashlights, or TVs, it would be understandable to think the “580” requirement in the table below is somehow a measure of brightness or what a driver sees, but it is not. They do not measure total light returned.Īs distance to a retroreflector decreases or increases, more or less light enters a detector respectively, but retroreflectivity measurements do not change. Measurements are taken from a particular spot within the cone of retroreflectivity. Retroreflectivity measurements indicate how efficiently a retroreflector returns light in a particular direction. ![]()
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