The requirements for goggles varies depending on the use.
Some examples of the many uses of goggles...
Cold weather: Most modern cold-weather goggles
have two layers of lens to prevent the interior from becoming "foggy". With
only a single lens, the interior water vapor condenses onto the lens because
the lens is colder than the vapor, although anti-fog agents can be used. The
reasoning behind dual layer lens is that the inner lens will be warm while the
outer lens will be cold. As long as the temperature of the inner lens is close
to that of the interior water vapor, the vapor should not condense. However, if
water vapor gets between the layers of the lens, condensation can occur between
the lenses and is almost impossible to get rid of; thus, properly constructed
and maintained dual-layer lenses should be air-tight to prevent water vapor
from getting in between the lenses. This type of goggle is best only for cold
weather. They would be too heavy, and too hot for use in most other activities.
Swimming: Must be watertight to prevent water,
such as salt water when swimming in the ocean, or chlorinated water when
swimming in a pool, from irritating the eyes or blurring vision. Allows
swimmers to see clearly underwater. They will not be usable more than a few
feet underwater, because the water pressure will press them tightly against the
face. Examples of these include the Swedish goggles.
Safety Lens glasses / goggles: Must be made of an unbreakable
material that prevents chunks of metal, wood, plastic, concrete, and so on from
hitting or piercing the eye. Usually has some sort of ventilation to prevent
sweat from building up inside the goggles and fogging the surface. Look for the
ANZI rating so you know your getting an OSHA approved Lens.
Blowtorch goggles: These protect the eyes from
glare and flying sparks and hot metal splashes while using or near as
blowtorch. This type of lens would NOT be dark enough for arc welding.
Motorcycle riding and other open-air activitie goggles /
glasses:
Prevents wind, insects, dust, and so on from hitting the eyes. Many people
believe that these type of goggles should perfectly seal the eye to keep out
all debris. Actually, if the goggles did perfectly seal, moisture from the eye
would cause the lens to fog and make wearing the goggles unsafe for driving.
Only swim goggles completely seal the eye, though many new styles have soft
foam inserts to cover the vents and block even the finest particles of sand and
dust. Though normally that is not necessary and does cause a certain amount of
fogging because it impedes the flow of air by a small degree.
Laboratory and Research Goggles: Combines impact
resistance with side shields to prevent chemical splashes reaching the eyes.
May also include laser protection which would be covered by EN 207 (Europe) and
ANSI Z 136 (United States). Examples of these include red adaptation goggles.
Racquet Ball Glasses: Protect the eyes from racquets swinging in an enclosed area and
from impact from hard rubber ball.
Winter sports: Protect the eyes from glare and
from icy particles flying up from the ground.
Astronomy and meteorology glasses / goggles: dark adaptor goggles
are used before going outside at night, in order to help the eyes adapt to the
dark.
Basketball glasses / goggles: Several NBA players have worn
goggles during play, including Kareem Abdul-Jabbar, James Worthy, Horace Grant,
Kurt Rambis and Amar'e Stoudemire; they prevent a fellow player from scratching
or hitting the eyes when trying to grab the basketball.
Aviation glasses / goggles: In open cockpit aircraft, such as old
biplanes, aviators, such as Amelia Earhart and Charles Kingsford Smith, would
wear goggles to help protect from the wind and are still in use today. Examples
of these include the AN-6530 goggles.
Virtual reality goggles / glasses: A virtual reality headset,
sometimes called "goggles", is a wrap-around visual interface to display
computer output. Commonly the computer display information is presented as a
three-dimensional representation of real-world environments. | 
