I am not sure if applying lemon directly to your skin would be a good thing, and this is def going to make your face sticky. I would think it would be irritating. But there are many alternatives, some lightening products do have lemon in them actually. Ole Henriksen Invigorating Night Gel has lemon extract and helps in keeping your skin tone even.
Lemon juice is pretty powerful and it does work to tighten pores and lighten discoloration but make sure you use a sunscreen because it does increase your skin's sensitivity to the sun causing even darker hyper-pigmentation of even hypo-pigmentation (white or light splotches)
Dilute with water to make a toner or use as a peel, leave on for 5 minutes, and rinse with cool or luke warm water to help close pores. Follow with sunscreen.
Lemon and water in a spray bottle for my hair in the summer. YEAH!!! Did this as a teen for natural highlights. Yeah, it does fade the skin so dilute it, rinse it and use with caution! Jan Brady rubbed it on her face to fade her freckles, remember!!???
I actually got some lemon juice on me when I was drinking iced tea outdoors and it actually left dark spots on my skin. I thought it was freckles at first, but it turned out to be the lemon juice. It was probably because I was in the sun, but I had tons of sunblock on.
If you use lemon juice on your skin, be sure to stay out of the sun.