LightType.Directional  

// Make the light a directional light
light.type = LightType.Directional;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        light.type = LightType.Directional;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        light.type = LightType.Directional