How do you make a timed auto clone to workspace?

local Model = game.Lighting.Model

while wait(5.1) do
    local ModelClone = Model:Clone()
    ModelClone.Parent = game.Workspace
end

The script you had was running the code once. Also, I recommend as ForeverBrown said that you don't store things in Lighting, store it in ServerStorage or ReplicatedStorage or something, not really sure. Scripts only execute once, unless they have events in or loops. To get something to repeat forever you can do

while wait() do -- if you put a number inside wait() it will repeat the code every x seconds.
    code here
end