A lamp could pass all the optical and protective tests in the catalog, but still failed during the first rainy season. The specification that determines this matter is called surge, and it is precisely the column most often left blank by buyers.

There are two paths for surges to reach outdoor lights. A direct lightning strike or landing nearby will induce fast, high-energy transients on overhead lines; while the switching of large loads and capacitor banks on the same power grid will produce lower-energy but much more frequent disturbances. Both are simulated using combined waves in IEC 61000-4-5, and are usually marked with waveforms of surge current 8/20 microseconds and surge voltage 1.2/50 microseconds.

The test level is important because it corresponds to the on-site installation method. Common published values are 2kV line-to-ground and 1kV line-to-line, which are suitable for areas where power is supplied by buried cables and where thunderstorm activity is weak. Light poles powered by overhead lines, roof installations, and areas with high incidence of thunderstorms should require 6 kV or 10 kV levels. Please also ask which level is applicable, and whether the protection is provided within the drive or by a separate lightning arrester-these two solutions are not equivalent.

If a stand-alone lightning arrester is used, IEC 61643-11 defines the level of coordination: Type 1 is used for main distribution boxes that may withstand part of the lightning current, Type 2 is used for distribution circuits, and Type 3 is used for local protection close to equipment. What the drive can withstand internally is only the part that reaches its terminals, so whether the upstream cooperation is in place determines whether it encounters an event that can survive.