var mn = 3; //MINIMUM SHADOW BLUR
var mx = 10; //MAXIMUM SHADOW BLUR
var loop = (mx-mn)+1; //LOOP GOING UP AND DOWN
var x = -1; //CONSTANT INCREMENTING VARIABLE
var p = mn-1; //MINIMUM SHADOW BEFORE FUNCTION (MUST 1 LESS THAN "var mn")
function glow(){
var v = $('#t').val(); //INPUT STRING
x++; //CONSTANTLY INCREMENTING
var g = (x%(loop*2)); //TO KEEP THE PIXELS GOING UP AND DOWN SMOOTHLY

if(g>=0&&g<=loop-1){
if(g==0){
p = mn-1;
}
p++;
}
if(g>=loop&&g<=(loop*2)-1){
if(g==loop){
p = mx+1;
}
p--;
}

$("#glo_txt").css({"text-shadow":"0 0 "+p+"px #12495d"});
setTimeout("glow()", 150);
}
glow(); //RUNS THE FUNCTION UPON PAGE LOAD
<input id="t" value="Enter text"><br>