A. novel wavelength tuning technique, applicable to shallow junction surface-emitting LED's, is shown to exhibit wavelength changes on the order of 50 nm, depending on current and gas environment. The tuning technique is external and is continuous, repeatable, reversible, controllable, and apparently nondestructive. Thermal and pressure changes in Eg do not appear to be dominant mechanisms. The dominant mechanism is suspected to involve surface effects, such as desorption of adsorbed gases, which depend upon self-heating in vacuo. The one-to-one relationship between diode voltage and peak emission wavelength suggests photon-assisted tunneling as the tuning mechanism, although surface band-bending changes may play some role. Surface effects alone, such as generated by UV illumination, are shown to yield noticeable LED wavelength shift, while bulk heating with red light of much higher average irradiance does not. This technique is, in principle a general technique independent of semiconductor material. The results described here should also have implications for optical-fiber communication, gas detection and identification, and space applications.