Theory Thursday #4 - Rays and Reflection

Welcome everyone to the fourth Theory Thursday!

If you are not interested in understanding how the world works, especially light and shadow, color and harmony, you should better skip reading this post and future Theory Thursday editions.
Opposed to the very direct and practical tutorials you will usually find here, these series of posts will go in depth to answer questions that many painters didn't even ask themselfes.

Be reminded that these posts are written by Raffa alone and reflect his understanding of the topics.
He is not always right and if you found an error or you want to discuss, use the comment section!

This week the topic will be:

Rays and Reflection

In this weeks edition we will go a bit deeper in the way light works.
As I already wrote in the first edition of Theory Thursday, light is an electromagnetic wave.

Without going too much into depth how this works in a physical way we need to understand 'light sources' of all kind emit these waves.

If you imagine a flashlight, it's basically a electromagnetic wave shotgun (sounds friggin' awesome) sending out light rays in a forward direction. Or a lightbulb sending out light rays all around it.

Light rays travel straight forward (most of the time... a black hole can bend light rays, that's why it is black :-) at the speed of light ( ehrm... yes, thanks captn obvious!).
In a vacuum it doesn't lose energie and continues to travel until it hits any kind of matter.
That's why we can see stars in the night sky, even though they are so far away and the light takes years to travel from them to earth so we can see it.

So when a light ray basically travels until it hits something.

This something can be any kind of matter, even air influences light rays in a certain way.
If it hits solid matter or an angry silverback gorilla that hates light rays it comes to a stop.
The energy transported by this wave gets absorbed by the object (that's why the sun gives warmth)

But what if the object is not a gorilla or the light ray doesn't get completely absorbed?
The same that happens with every object that hits something and isn't destroyed.

It will be reflected!

A good example is a laser pointer and a mirror.
A mirror is not absorbing a lot of the light the laser pointer is producing, the laser point will be reflected back (don't look into the laser pointer if you try this out ;-)
The opposite is true for black, rough materials.
Black is absorbing a lot of the visible spectrum and so almost nothing is reflected back (that's why we perceive black as black... it's basically just very little light getting into our eyes)

That's why black cars are much hotter inside in summer than white cars. They absorb a lot of energy and act like an energy sponge. In this case the energy will be converted to heat.

So, why then are some materials so different, even when they have the same color?
Maybe you already read the word. Roughness.

How a light ray is reflected also depends on the surface of the object.

When a light ray hits a surface it is reflected back in the same angle of incidence.
Watch out, this 'simple' way of explaining it basically only works for solid, non conductive materials (not metals and not transparent or transluscent).
We will go more into detail on this topic in a later isse of Theory Thursday ;)

Ok, so if the surface is perfectly smooth, the ray will be reflected back in the same angle it hit the surface (measured perpendicular to the surface).

Look at the above illustration and you will quickly understand what is the difference between smooth and rough materials. Rough materials scatter the light and create a much softer reflection.

 

Here you can see two spheres, one is more a wool like material, the other one is polished.
A sharp reflection creates a shark highlight.

Hopefully this article explained the basics about reflected light rays.
What can you do with this knowledge?
Understanding materials and try to paint them on miniatures :)
Effects like non metallic metal are waiting for you ;)

I think at this point I will stop with this weeks Theory Thursday and go on with reflections and bouncing light rays next week!

_______________________________________________________________________________
You want to support Massive Voodoo? 
If you like to support or say thanks the monkeys of Massive Voodoo in what they do, please feel invited to drop a jungle donation in their direction via paypal or check their miniatures they got on sale here.
_______________________________________________________________________________