Humorist James Thurber once wrote, "There are two kinds of light — the glow that illuminates and the glare that obscures." He may as well have been talking about the ocean at night. In today's light-polluted world, the beauty of the night can all-too-often be obscured by the glare of businesses that surround the beaches of the world. But if you look closely, beyond that man-made light, you might see something special: the quiet glow of bioluminescence.

Bioluminescent tides, which shine quietly in the darkness, exist in many locations throughout the world. Sometimes these glowing waters seem like little twinkling stars suspended in the water. Other times they glow with almost enough brightness to read.

This phosphorescence is usually caused by algae suspended in the water. Much like fireflies flitting through the air, the algae (of a wide variety of species) emit a glow whenever they are jostled. Sometimes that's caused by the tides rolling in and out. Other times it can be caused by the motion of a boat or a fish moving through the water. Once in a while, the glow is even strong enough to be created by the gentle stroke of a finger.

Here are several places around the world where you can go to see the waters glow:

1. The Blue Grotto, Malta

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Reachable only via specially licensed boat, the Blue Grotto of Malta is said to be one of the most spectacular natural sights in the world. These oceanic caves on the small island of Filfa are surrounded by tall cliffs that are constantly pounded by waves, producing the phosphorescent glow for which they are known. Blue Grotto is actually just one of nine caves, all of which are popular tourist destinations. Filfa itself, located more than three miles out to sea, is completely uninhabited except for several species of birds and a subspecies of wall lizard that can be found nowhere else.

2. Bioluminescent Bay, Puerto Rico

The waves at these three bioluminescent lagoons aren't really strong enough to photograph, but that doesn't stop them from being a popular tourist spectacle, a place where people can kayak into the glowing waters at night. The three bays glow a gentle green, a situation that is natural but has been enhanced by humans, who mostly cut them off from the surrounding ocean a couple of centuries ago.

Unfortunately, one of these three lagoons hasn't been glowing as much lately. Hopefully the same fate won't befall the other two.

3. San Diego, California

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You have to time things just right if you hope to see the glowing tides in San Diego. They don't happen every year — in fact, scientists don't yet know how to predict when they will happen. But when they do happen, they happen in a big way and people flock to the beaches to photograph the bright blue tides. The San Diego tides may or may not glow again this year, but they have glowed more years than not in the past decade. So who knows, if you're in San Diego, try a walk on the beach at night. You just might be surprised.

4. Navarre Beach, Florida

The warm summer months are a great time to go kayaking in Florida, especially around Indian River and Mosquito Lagoon. There, when the plankton is right, the water glows as both boaters and fish move through the water. According to the Florida tourism website, the effect makes "fish look like blue comets." The effect can also be seen from time to time on the ocean beaches.

5. Toyama Bay, Japan

This one is just a little bit different from the rest. Every other site we have profiled so far glows because of the algae present in the water. The glow at Toyama Bay comes not from phytoplankton but from a phosphorescent creature called the firefly squid. Every year from March to June, the bay becomes inundated with millions of these three-inch squid, which come up from the depths of the ocean to breed. As they fill the waters and beaches, both fishermen and tourist operations spring into action.

6. Matsu Islands, Taiwan

So-called "blue tears" had been causing quite the stir around the Matsu Islands. Researchers from the National Taiwan Ocean University conducted a four-month study of the waters, taking samples and studying organisms in the water. According to the China Post, the researchers pinpointed Noctiluca scintillans as the sea-glowing culprit. They will take another year to continue to study the water, seeing if other organisms are contributing to the blue waters, and they will work with businesses to identify a "blue tears" season, presumably to optimize tourism.