How to blur the screen?

I want this code to blur the screen when you join the game. The code to unblur the screen works but the code to blur it doesn't. The blur is for the menu.

local exit = script.Parent.ExitButton
local play = script.Parent.PlayButton
local rules = script.Parent.RulesButton

local frame = script.Parent
local blur = game.Lighting.Menu_Blur

local rulesframe = script.Parent.Parent.RulesFrame
local health = script.Parent.Parent.health

local rulesclose = rulesframe.CloseButton

game.Players.PlayerAdded:Connect(function()
    wait(1)
    frame:TweenPosition(UDim2.new(-0.001, 0,-0, 0),"Out","Quad")
    health.Visible = false
    blur.Enabled = true <-- this is the code thats not working
end)