// Pulse light's intensity over time

var duration : float= 1.0;
function Update() {
    // argument for cosine
    var phi : float = Time.time / duration * 2 * Mathf.PI;
    // get cosine and transform from -1..1 to 0..1 range
    var amplitude : float = Mathf.Cos( phi ) * 0.5 + 0.5;
    // set light color
    light.intensity = amplitude;
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public float duration = 1.0F;
    void Update() {
        float phi = Time.time / duration * 2 * Mathf.PI;
        float amplitude = Mathf.Cos(phi) * 0.5F + 0.5F;
        light.intensity = amplitude;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public duration as single = 1.0F

    def Update():
        phi as single = (((Time.time / duration) * 2) * Mathf.PI)
        amplitude as single = ((Mathf.Cos(phi) * 0.5F) + 0.5F)
        light.intensity = amplitude