Light

tButtons = {
        { text = "ON", x = 1, y = 1, col = colours.lime },
        { text = "OFF", x = 1, y = 1, col = colours.red }
}

local function isValidClick( tab, mx, my )
        for _, v in pairs( tab ) do
                if mx >= v.x and mx <= v.x + #v.text - 1
                and my == v.y then
                        return true, v.text
                end
        end
        return false, nil
end

local function printTable( tab )
        for _, v in pairs( tab ) do
                term.setCursorPos( v.x, v.y )
                term.setBackgroundColour( v.col )
                write( v.text )
        end
end

printTable( tButtons )

while true do
        local event, but, X, Y = os.pullEvent()
        if event == "monitor_touch" then
                bValidClick, sText = isValidClick( tButtons, X, Y )
                if bValidClick then
                        if sText == "ON" then
                                redstone.setOutput( "back", true )
                        elseif sText == "OFF"
                                redstone.setOutput( "back", false )
                        end
                end
        end
end