The carbonite itself just forms a matrix for a stasis field. Without it, such a field is so unstable that it takes Jedi-tweaking to make it safe for living things, and even with the carbonite, it can cause tissue damage and death if the field doesn’t take effect simultaneously across the subject’s entire body. Han did suffer from temporary blindness and other side effects upon coming out of the field because the field stabilized around his torso first, subjecting the rest of his body to oxygen deprivation and odd blood pressure effects. This is a common effect when relatively large creatures are subjected to carbonite stasis, and is referred to as hibernation sickness.
The jets of vapor are part of a cooling system. Solid carbonite sublimes slowly at temperatures in the same general range as the body temperature of many common endothermic life forms; the carbonite shell had to be cooled slightly until the field was established, or Han’s body heat would have caused it to evaporate. When the field was shut down, the thin part of the shell sublimed almost immediately; the main block would take much longer. Curiously, this phenomenon is accompanied by emission of visible and infrared light. When incident light strikes the stasis-stabilized carbonite, most of it is reflected; however, some percentage of photons enters microscopic pores in the carbonite matrix and becomes trapped in the stasis field. With prolonged exposure, the field can absorb substantial amounts of light. When the field is withdrawn, these photons are able to escape, making it appear that the carbonite (or its contents) are emitting light. Naturally, the parts of the carbonite exposed to the most light will radiate most strongly. Pro tip: don’t leave carbonite-encased objects in the sun too long, or you run the risk of being blinded or burned when you extract them. Exposing it to lots of ionizing radiation is probably unwise, too.