And you can get very small keychain sized flashlights, some smaller than a clicker, so you don't necessarily have to lug a big flashlight around. Once the puppy associates the light with a treat, he will start watching for it. When using a clicker I usually wear it on an elastic around my wrist so it's always there and doesn't get lost, you could do the same with a small flashlight.
https://www.amazon.com/Uniclife-Key...793&sprefix=keychain+flas,aps,653&sr=8-7&th=1
https://www.amazon.com/Uniclife-Key...793&sprefix=keychain+flas,aps,653&sr=8-7&th=1