controle lâmpada

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8"/>
    <title></title>
</head>
<body>
    <center>
<h1>JS Lampada</h1>
    <img src="off.jpg" alt="Lâmpada" id="lamp">
    <form>
        <input type="button" value="ON" onclick="on()">
        <input type="button" value="OFF" onclick="off()">
        <input type="button" value="BLINK" onclick="blink()">
    </form>
</center>
<script src="arquivo.js"></script>
</body>
</html>
function on(){
    document.getElementById("lamp").src="on.jpg";
}
function off(){
    document.getElementById("lamp").src="off.jpg";
}
function blink(){
    var intervalo = 0;
    var contador = 0;
    while(contador<10){
        intervalo+= 300;
        setTimeout("document.getElementById('lamp').src='on.jpg';",intervalo);
        intervalo+= 300;
        setTimeout("document.getElementById('lamp').src='off.jpg';",intervalo);
        contador++;
    }
}