Light.spotAngle

Description

The angle of the light's spotlight cone in degrees.

This is used primarily for Spot lights and has no effect for Point lights See Also: Light component.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public float interval = 0.3F;
    public float minAngle = 10;
    public float maxAngle = 90;
    public float timeLeft;
    public Light lt;
    void Start() {
        lt = GetComponent<Light>();
        lt.type = LightType.Spot;
        timeLeft = interval;
    }
    void Update() {
        timeLeft -= Time.deltaTime;
        if (timeLeft < 0.0F) {
            timeLeft = interval;
            lt.spotAngle = Random.Range(minAngle, maxAngle);
        }
    }
}