var innermost = 15;
var start = 30;
var growth = 1.2;

var radius = innermost;
for (var i = 0; radius < Math.min(window.innerWidth, window.innerHeight)/2; ++i) {
    e = document.createElement("div");
    e.className = "circle";
    e.style.height = (2*radius) + "px";
    e.style.width = (2*radius) + "px";
    document.getElementById("circles").appendChild(e);

    radius += start * Math.pow(growth, i);
}

/*      document.getElementsByClassName("light")[0].animate(
        [
        { top: "50%", left: "50%" },
        { top: "50%", left: "50%", offset: 0.9 },
        { top: "50%", left: "50%" }
        ],
        { duration: 10000, iterations: Infinity }
        );*/