Karl Townsend wrote:

I'm about to purchase a photo eye. http://tinyurl.com/6bjmeb

What's the difference between PNP and NPN? I just want an eye that's NC
powered by 12VDC that uses very little power.

Karl

On top of what everyone else said, pay close attention to the output
current rating as these are not contact closure outputs and have very
low current ratings. You need to add a relay if you need to switch
anything of significance.