Sunday, November 4, 2012

The Beauty of Science #3: UV Radiation, Visible Light, and Color

Welcome to another Beauty of Science post. I apologize that it's been a while since the last one, but, well, I went and got married and stuff. Turns out that's very time consuming.

Today I meant to talk about sunscreens - the difference between "physical" and "chemical" sunscreens, common ingredients, etc. However, I realized that a post about sunscreens needs to be prefaced with a conversation about UV radiation and light. So that's what we're going to address first. It's also going to include a small discussion on color, which I think will interest you.
Electromagnetic spectrum. This graphic illustrates the relative length of waves, from longest to shortest.
(source)
Let's start with the electromagnetic spectrum, which is simply a scale of all the types of energy in the universe. You're familiar with most of these already: radio waves are indeed the kind you pick up with your car radio, microwaves are used in microwave ovens to heat your food, the human eye detects visible light and that's how we see, and then there's ultraviolet radiation - the kind you protect against with sunscreen (yes, and then there are x-rays and gamma radiation, but we won't go in to all of that here).

Different types of electromagnetic radiation are characterized by different wavelengths.

All electromagnetic radiation types are types of energies. Energy can be absorbed by molecules. This energy is used to break or form bonds (remember bonds?) which is what promotes activity. Different molecules absorb different energies, which means that they absorb different wavelengths. Does that make sense?
Which one are you? Haha.

It's kind of like Skittles, you know. Some people only eat the red ones. Some people only eat the green ones. Some people eat all of them. (This is an extremely simplified analogy, but hopefully it helps).

So, what we're interested in, is that certain molecules can absorb UV radiation. The problem we run into as humans is that sometimes we can absorb too much, and that can be detrimental. We'll talk about that in the next session.

The other thing I wanted to point out - and this is pretty cool - is the science behind color. Molecules absorb energy, right? Well, visible light is a form of energy - you can see it on the scale up there, nestled between infrared radiation and ultraviolet radiation. Some molecules absorb wavelengths of certain colors, and the ones that they don't absorb are responsible for the color that you see.
source

For example, here is a molecule that occurs in food to give them a characteristic color. Generally, the more of a colored molecule an item has, the more intense the color. (This is actually an example of pigments producing color - there are other methods, all involving light, but we won't go into that here.)
Since β-carotene absorbs green-blue light, the molecule appears orange (or variations of red-orange-yellow). You can see that best by looking at a color wheel. Look at that: science meets art.

You can predict what color things will be by knowing what color they absorb. Also: if something is white, it absorbs no visible light. If it's black, it absorbs all visible light - that's why black clothing can be hot. For more information, here's a good resource.

Okay! Hope that was at least interesting to you. Next time we'll be talking about UV radiation specifically, as well as common sunscreen ingredients and types. As always, please let me know if you have any questions or ideas for future posts! Any feedback is always appreciated.