Can I use the outlet to plug in a 120v light or must it be a 240v?
(looks like a standard 120v outlet one finds in a house).
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That is a 120v 15 amp receptacle. I hope you have a neutral feed to the pool or a transformer that is creating the 120v.
If this has been installed in the last 20 years, it should have a proper neutral and should be safe to use.
If it is an older system that had an added 120v circuit, then there may be some safety risks because the neutral for the light might be going back on the ground for the pool.
When skin is wet, the resistance of the skin is reduced and shocks affect us at lower voltages, this combined with muscle convulsions can cause drowning at low levels, so I always like to know the system prior to saying it is safe.
If your pool has a 4 wire feed and everything is properly wired and grounded, then it should be fine to plug in to that receptacle with a 120v device.