Today, ten days after I decided to do a germination test on these loofah seeds, I checked on them to see how many had begun to grow. Eighty percent over ten days at 70 degrees - better than I expected! I'll test them again in the spring after storing them in a dry, dark spot over the winter.
Germination tests are a great way to check seeds you already have, especially older ones that you're unsure of, to see if they're still viable. An easy way to do this is to fold ten seeds into a damp paper towel and place the paper towel in a sealable baggie. Put the baggie near a sunny window and wait about a week (longer if the seed packet says they need a little longer), then open the baggie to see how many have sprouted. Make sure to keep the paper towel damp while trying to get your seeds to sprout (this shouldn't be an issue if the baggie is sealed).
Fun fact: Many seeds don't actually need any light to germinate. They just need a warm, moist environment. Once they've germinated, though, you'll need to get them to a sunny spot so they can continue to grow properly.