Check out these online images of the electromagnetic spectrum — one or more of them should help you in your unit and you can use them on your interactive whiteboard:
Reflection, refraction, and absorption video lesson.
Can your students make colored shadows? Here is a lesson plan that shows you how.
Optical illusions presentation — tells why we see them and how our brain fools us. Then presents a number of optical illusions for you to share with your class. Great on your interactive whiteboard.
Light Speed
The speed of light is not as simple as it might seem. Take a look at this for more information.