
So Zed can see a character's ambient amounts of light and darkness--how much they shine, how much darkness they've got coming off of them, that sort of thing. In his canon, light is basically all sorts of positive emotions and concepts, for example: love, happiness, imagination, or self-sacrifice. Darkness would be the more negative aspects of things, like anger, fear, loneliness, sadness, and so on and so forth. He's from a kids' show, it ain't subtle.
The important questions here are:
Can Zed see your character's levels of light and darkness? and
If so, what will he see?
Zed is also a being of darkness, and looking into his eyes is not unlike staring into a fathomless void of infinite darkness (because in canon, he's the worst of the worst). This leaves him with the ability to terrify or unnerve people with extended eye contact. He cannot control this but is aware it happens. I've kind of been rolling with this as more effective on children or people with weak wills, but to be thorough:
Will prolonged direct eye contact with Zed have any effect on your character?