Question

Are there any brown dwarfs optically visible from Earth?

Answer 1

Optically no. We know they are there from their infrared spectrum that we can detect with specialized detectors.

Explanation:

Brown dwarfs are essentially failed stars - they lacked the mass to become stars and start their fusion reactions (which is what produces visible light).

So, no, there are no brown dwarfs that are optically visible. But they do emit infrared and other less energetic waves (they still are hot and so produce energy waves). Detectors on Earth can capture that energy and study brown dwarfs.

Here's more about brown dwarfs and the detection of them:
http://www.nasa.gov/vision/universe/starsgalaxies/brown_dwarf_detectives.html