Some people will say, "These lights are safe, because they were made for outdoor use in the rain".
First of all, this is assuming that the lights were put together correctly in the first place. Open up a few and check for yourself to see if the ground is connected properly, or if it was just cut off completely. If it's not connected properly, you can forget any safe usage, anywhere. As a matter of fact, if the ground is not connected properly, usage in the corrosive saltwater environment of a
sump is (at least) very dangerous, and in my opinion could be described as deadly, when the operator is an unsuspecting and non-electrically-aware consumer (or worse, their children, standing on a wet floor) who bought the scrubber thinking the manufacturer did all the proper safety designs and certifications.
Second, even if it was put together correctly, usage in an outdoor area or garden usually means the light will be staked into the ground, or will be attached to a metal conduit, both of which provide a ground path if the internal 240/120 volt circuit gets shorted to the metal case. Plus, you don't normally touch, grab, or usually even go near these outdoor lights in a garden. So even if they shorted internally to the metal case, and even if the ground wire were missing, you would not be anywhere near it.
Third, the water falling onto the lights in a garden area is just freshwater. Compare these things to a saltwater
sump:
It's bad enough that the ground might not be connected, but regardless, the installation is on the top of
sump that is not grounded. It's not a garden bed, and it's not a metal conduit grounded to a house. Instead it's an electrically-floating acrylic box filled with water. It's a really, really bad place to have a possibly non-grounded product, or even a grounded product that is likely to eventually leak.
And the usage requirements of these scrubbers requires weekly, and sometimes daily, touching and grabbing of the lights. With wet hands, and while standing on a wet floor. Ask any licensed electrician if he would like to be doing this.
The 240/120 volt power supply in these lights is inside the metal case which holds the rubber seal in place. All metal corrodes, especially aluminum, and especially in saltwater, and when the metal corrodes enough around the seal, the seal will leak. And the most dripped-on part of the light is the top, and that is directly above the internal power. So, the water drips down directly onto the high voltage inside. Look at how the lights are usually mounted: the seam of the seal at the top is directly over the internal power supply.