Just wondering what is the best way to measure the lighting levels at a crosswalk. The plane should be 1.5m above ground. My question would be is it best to use the horizontal option with a Z value of 1.5m or use the vertical option perpendicular to a line with a Z value of 1.5m. Is it more complicated than that? Some cases you get quite different results.
You say 'measure', but I assume you mean 'calculate'.
If you're trying to light a pedestrian crossing, it would be highly likely you're trying to show compliance with a Standard, especially since you've said at a height of 1.5m above ground. This indicates you've been told where to put a calc plane. The answer you need should also be in the location where the concept of a raised 1.5m calc plane is.
You're correct that the horizontal and vertical result gets quite different results at times, in most instances it should vary.
Check the Standard. If it is not explicit about the horizontal and vertical requirement, it's very poorly set up. As an example, the Australian Standard is very clear about exactly where to place your calculation points, and how many you should use, and which direction they should face (vertical calculation points usually require additional information on which direction they should face, and again you'll get erroneous results if they're facing the wrong way).
Thanks, Lou. Our standards are pretty good where to put the calculation and at what spacing. I was just wondering which line calculation I should use. I ended up using the variable - meter aiming point using the stopping sight distance for the roundabout speed and giving it an elevation of 1.5m. It all looks good.