Light.shadows  

// make the light cast hard shadows
light.shadows = LightShadows.Hard;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        light.shadows = LightShadows.Hard;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        light.shadows = LightShadows.Hard