There seems to be a problem with Chrome processing, maybe you have Chrome 32 bit installed ?
You can do two things to improve quality. First set the renderer attribute
renderer.shadowMapType = THREE.PCFSoftShadowMap;
and then you can also increase the shadow map size of your light with:
light.shadowMapWidth = 1024; // default is 512
light.shadowMapHeight = 1024; // default is 512
as can be seen from this problem: The quality of the shadow shadow Three.js in Chrome / MacOS?
" , . , Firefox , . , Chrome MacBook Pro 2009 , 2012 .
, FXAA . . "
: Three.js