Lamp

using UnityEngine;
using System.Collections;

public class Lamp : MonoBehaviour
{
    // set these up in the inspector
    // the spriteRenderers will be dragged in from the scene
    public SpriteRenderer lampSpriteRenderer, skySpriteRenderer;
    // these sprites are Assets, they should be dragged in from the project folder
    public Sprite lampOn, lampOff;
    public Sprite skyOn, skyOff;

    // have to add a boxcollider (or spherecollider) to this to make it actually clickable. set it to be a trigger (isTrigger checkbox)
    void OnMouseDown()
    {
        // if the lamp spriteRenderer (thing that renders the lamp onscreen) has the lampOn sprite, then ...
        if (lampSpriteRenderer.sprite == lampOn)
        {
            // we want ot set it off
            lampSpriteRenderer.sprite = lampOff;
            // and set the sky off too!
            skySpriteRenderer.sprite = skyOff;
        }
        // if the lamp spriteRenderer (thing that renders the lamp onscreen) is NOT showing the lampOn sprite, we can assume it's showing the lampOff sprite...
        else
        {
            // so turn the lamp on
            lampSpriteRenderer.sprite = lampOn;
            // and the sky too! :)
            skySpriteRenderer.sprite = skyOn;
        }
    }
}