light.areaSize = Vector2(5, 2);

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        light.areaSize = new Vector2(5, 2);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        light.areaSize = Vector2(5, 2)