This has nothing to do with Photoshop. The problem is that Windows Photo Viewer displays the image incorrectly. Apparently it's choking on the display profile, while Photoshop manages to work with it.
Both applications are fully color managed and should display identically. If they don't the problem is nearly always the display profile.
Try to set sRGB as default display profile in Windows. If the difference disappears you know you have a bad profile and need to replace it. If you don't have a calibrator to make a new profile, just use sRGB for now. Manufacturer-supplied profiles are notoriously defective in any number of ways and should be avoided.
I appreciate your help,
I should probably have added this to the original post, but I do share my work with others and no matter if it's in windows photo viewer or online, both myself and others see it darker than it is in my Photoshop workspace. This is what makes me think it has something to do with the way Photoshop saves my images.
I checked out what you said and I think you might be on to something. It seems to have been set on a BenQ profile:
I tried both switching to a sRGB profile and trying to save a file, and calibrating my monitors for a profile and saving. Both still turned out too dark.
I tried to convert the PSD to the BenQ profile and saving it, it turned out way too light.
I think there's something here, any ideas?
With some further testing I think this is the problem. I got it almost working flawlessly, so I guess I will play around with these settings tomorrow and then see if things work out.
Thanks for the help!
Thank you! That fixed the problem for me.