Tempered Glass Lamp Shade

Typical lamp shade for a floor lamp
A tempered glass lamp shade’s purpose is to protect the eye from the bulb's glare and to direct light from the bulb in the lamp into the room.
A common form of the tempered glass lamp shade on a floor lamp, for example, uses cloth or paper with a loose weave to block significant amounts of light in a horizontal direction. At the same time, the shade permits light to flow from the top and bottom. This allows light to be more focused below the shade – perhaps for the use of the person sitting in a nearby chair, to permit them to read more easily – and some light to flow to the ceiling, where it is reflected and becomes part of the ambient light in the room.
By blocking the light horizontally, those sitting or walking are unlikely to have the direct glare of the bulb hit them in the eye. Instead, they have the softer reflected light from the ceiling and the much-diffused light through the shade.
A torchiere shade will, instead, project most of the light upwards. Torchieres are part of accent lighting and general lighting, rather than task lighting.

Lamp shade for a table lamp
Like a floor lamp, a table lamp’s light is directed by its shade. A small amount of light flows through the loose weave of the shade itself. The majority of the light is directed downwards and out at something of an angle, permitting light to flow over a larger area than the lamp itself. The height of the table lamp and the width of the lower shade will determine the area lit by such a lamp and shade.

Smaller lamp shades for task lights
A smaller lampshade focuses the light even more narrowly. A lampshade like this, often used as task lighting, focuses more light in that area. The narrow focus also makes it less likely, in a dark room, that the light will bother those not in the immediate circle of the light cast from that bulb. This is a particularly useful configuration for bedtime reading lights or reading lights for a room in which others may be watching television.

Pendant lamp shade
A shiny metallic pendant lamp shade closed at the top focuses all the light from its bulb downwards. This makes the configuration especially useful for task lighting of a surface like a work table or kitchen counter. The shiny surface also reflects ambient light in the room.

Take a cue from a restaurant
Take lighting cues from restaurants. Use lampshades on lights over tables to make sure that people can comfortably see what they're eating, but keep the general ambient lighting low for relaxation (brightly lit restaurants are usually those that want to promote fast table turnover). Restaurants also often have wall sconces with lampshades that direct light downwards towards the edge of the floor, to help safely light walking paths and doorways.

Chinese lantern lamp shade
In the style of Chinese lanterns, paper lampshades that surround the whole bulb disperse light more diffusely, rather than in a particular focus area. These, then, are more useful as decoration items and to add to the general light in the room.