Ambient light emitted by high-temperature black smokers and flange pools on the Juan de Fuca Ridge was imaged using a new spectral imaging camera. Most of the light is emitted at long wavelengths (700--1000 nm) and corresponds well to thermal radiation from a body at the same temperature as the vents/flanges. However, black smokers also emit time-varying radiation in the visible region (400--650 nm) which cannot be explained by a thermal source. This visible radiation is 1--2 orders of magnitude greater than would be expected for purely thermal radiation; it exhibits variation with time, despite relatively constant vent temperatures; and it is not associated with the hottest part of the plume (i.e. the orifice). Flange pools do not exhibit excess visible light over that for a thermal source, suggesting that the light at smokers is caused by mechanisms related to turbulence, mixing, or precipitation. ¿ 2000 American Geophysical Union