This study found Vitamin E in tablets degraded when exposed to light over a period of time. This study found Vitamin E and Vitamin A in parenteral nutrition packages degraded when exposed to light. And this book confirms Vitamin E is sensitive to heat and light (which is one of the reasons we add it in the cool down phase). So we've established that Vitamin E is sensitive to light.
Vitamin E degrades because of photo-oxidation. (A double bond interacts with a singlet oxygen (1 oxygen atom), which is produced by the light. It is highly reactive with unsaturated lipids.)
Interestingly enough, the Handbook of Preservatives doesn't recommend that we store it away from light; it notes that it darkens on exposure to light, but makes no special mention of how we should store tocopherols, but it notes it for other types of tocopherols. In this book, it is noted that a-tocopherol is "quite unstable and light sensitive when used in topical formulations" and so the "active hydroxyl group is, therefore, usually protected by esterification by acetate." (This book says the same thing.)
Esterification is "an alcohol or (of an alcohol) combined with an acid, to form an ester". (Wikipedia)
It appears there are two answers as to why we get our Vitamin E in clear or frosted bottles. What we get is often tocopherol acetate (see this product at Lotioncrafter), which is more stable that non-acetate versions of Vitamin E. And secondly, Vitamin E isn't so crazy unstable that it can't be in light at all. Much like our carrier oils, it's recommended we keep our Vitamin E in a cool dark place so we reduce the exposure to heat and light, but it isn't going to be ruined if we leave it on our counters for a day or two. Having said this, I think it's a wise idea to keep your Vitamin E where you keep your oils!
As an aside, in the summer months, I recommend getting your oils into the fridge or freezer. Yes, you can freeze oils! Similar questions and answers can be found in the frequently asked questions section of this blog!
When it comes to Vitamin C or ascorbic acid, its instability is about more than light sensitivity. It's also sensitive to pH - preferring pH 3 or less - and it's unstable in water. This is why we need to use a different version of Vitamin C, a version that has been esterified to make it more stable. Look for something like ascorbyl palmitate or other, more stable Vitamin C if you want to make products that contain it.
As an aside, the instability of Vitamin C and expense of the other forms of it are the main reasons you don't see Vitamin C sera on this blog. I'm asked all the time about these products, but I haven't made them because of this instability! It's not as easy as putting a Vitamin C tablet into some water and calling it a serum. You have to find the right kind of Vitamin C and make sure you're formulating it correctly, testing the pH, and so on. If you're interested in making one, here's a recipe from Lotioncrafter using tetrahexyldecyl ascorbate in a water free base.
Want to know more about what is sensitive to light? Check out this chart! As you can see, Vitamin E and C aren't as sensitive as Vitamins A, D, and K, or riboflavin.
Interestingly, if you've ever wondered if you could use things like Vitamin E or Panthenol in your alkaline soaps, look at the last line of the chart for your answer. (The short answer is no, they don't like alkaline environments.) But you could use Vitamin E in an acidic environment, like a lotion with loads of AHAs!