The 20-year-old marked his full debut with a first professional goal as the Bees beat AFC Wimbledon 5-3 in the Johnstone's Paint Trophy on Tuesday night.
Kernaghan said: "I am delighted for Luke.
"It has been a difficult year-and-a-half to two years for him. He has never been quite up to full match speed, from our perspective in the first team, until now.
"This pre-season he has looked very lively and very direct.
"I look at him as an Alan Shearer type; he has a touch and a whack at the goal. Quite a lot of times they go in the net.
"We are happy he is up to match fitness. He showed his ability and hopefully we will see more of that."