Why can I not turn my pc screen off?

I tried figuring this out but it doesn't work

local l3 = workspace.screen
local s1 = workspace.pc

function onClick()
	wait(0.1)
  	if l3.SurfaceLight.Brightness == 1 then
      	l3.SurfaceLight.Brightness = 0
        l3.Decal.Transparency = 1
    else
	    l3.Decal.Transparency = 0 
        l3.SurfaceLight.Brightness = 1
      end
    end
s1.ClickDetector.MouseClick:connect(onClick)