SOURCE

$(document).on("mousemove", function (e) {
  $(".light").fadeIn();
  $(".light").css("top", e.pageY - 100);
  $(".light").css("left", e.pageX - 100);
});

<css-doodle grid="20">
  :doodle {
  grid-gap: 10px;
  width: 2px;
  height: 2px;
  }
  :container {
  width:100vw;
  height:100vh;
  background:#3498db;
  padding: 10px;
  }
  :before{
  content:@index;
  color:@pick('#000000','#090909');
  font-weight: 900;
  }
  border:3px solid black;
  border-radius:5px
</css-doodle>
<div class="light"></div>

body {
  overflow: hidden;
}
.light {
  content: "";
  position: absolute;
  width: 200px;
  height: 200px;
  background: white;
  border-radius: 100%;
  mix-blend-mode: color-dodge;
  box-shadow: 0 0 40px 40px white;
  display: none;
}