What do you add to make it so it checks how long the light is on?

What do you add to make it so it checks how long the light is on. Thanks.

-- ProductOfDevs

local battery = 100

function onClicked()
    if battery ~= 0 then
        if script.Parent.PointLight.Enabled == false then
            script.Parent.Sound:Play()
            script.Parent.PointLight.Enabled = true
            script.Parent.Material = 'Neon'
        elseif script.Parent.PointLight.Enabled == true then
            script.Parent.Sound:Play()
            script.Parent.PointLight.Enabled = false
            script.Parent.Material = 'Sand'
        end
    end
end

script.Parent.ClickDetector.MouseClick:Connect(onClicked)