Library code: GLASS Screen

local modem = peripheral.wrap('top')
modem.open(2)
while true do
    local event, modemSide, senderChannel, replyChannel, message, senderDistance = os.pullEvent('modem_message')
    if message == 'on' then
        redstone.setOutput('bottom',true)
        modem.transmit(replyChannel, 2, 'turned on')
    elseif message == 'off' then
        redstone.setOutput('bottom',false)
        modem.transmit(replyChannel, 2, 'turned off')
    else
        modem.transmit(replyChannel, 2, 'invalid message')
    end
end