Yes, it seems ironic, but light can be turned into the ultimate dark monster. It's called a Kubelblitz (German for "ball lightening"), but a black hole can be made from either mass or energy. Einstein's famous equation E=mc^2 shows that energy and mass are equivalent things, mass can be turned into energy, and energy can be turned into mass. So in theory, the universe's smallest black hole would be one that concentrates 1 Planck Mass into a volume of 1 Planck Volume. You could just as easily replace the 1 Planck Mass with 1 Planck Energy, and you would have the same black hole.

1 Planck Mass isn't very big, it's not even as heavy as a grain of sand. 1 Planck Energy also isn't very big, it's not even hot enough to heat your morning coffee. 1 Planck Volume is incredibly small, it's trillions upon trillions of times smaller than any atom; it's smaller in relation to atoms, as atoms are in relation to us. But if you put any of these tiny things together, you have enough to create a tiny black hole.