Redirect non admin users to the home page after logging in. - Original Source (http://tommcfarlin.com/redirect-non-admin/)

function.php

// Redirect non-admins to the homepage after logging into the site.
function nonadmin_login_redirect( $redirect_to, $request, $user  ) {
	return ( is_array( $user->roles ) && in_array( 'administrator', $user->roles ) ) ? admin_url() : site_url();
}
add_filter( 'login_redirect', 'nonadmin_login_redirect', 10, 3 );