Hello and welcome to Module 3. Congratulations for staying with us and making it this far through the course! So at this point of the course, we're about halfway through our journey on the electromagnetic spectrum. In the past few modules, we have been looking in detail at each of the non-ionizing radiations. We've looked at their different frequencies and their key properties. We've also discussed how they are not particularly harmful to humans, except for the fact that they can be associated with sources of heat and heating effects. In this module, we are going to continue our journey along the electromagnetic spectrum. This time, stopping at visible light and ultraviolet light. With these two radiations, we will explore the fascinating topic of light as radiation. We'll also examine the crucial impact these radiations have on life here on Earth. Now, before we proceed, let's recap on a couple of things we learned back in our previous modules with regard to how radiations interact with matter. I'll give you a few moments to answer these questions. Electromagnetic radiations refract, scatter, and are absorbed by structures similar in scale size to the wavelength of the radiation. So ELF waves are large in wavelength. They can only interact with structures equal in size, like mountains. By the time we get down to the shortest wavelengths in the region of ultraviolet light, we're starting to get down to the size where radiation is refracted, scattered, and absorbed by atoms and by subatomic particles like electrons. At these smaller wavelengths, there is another process, ionization. In this module, we will look at more detail at how radiations like ultraviolet ionize atoms directly and indirectly. This is important when these radiations interact with the cells of our body. They can cause damage through ionization. We will discuss some of the ways that radiation causes biological damage and the ultimate effects this can have on cells. Finally, we will learn a little bit about the billions and billions of times per day our cell seek out and repair this damage, and in most cases, protect us from the harmful effects. So let's dive right in. I hope you enjoy this module.