courtesy Ge Lighting

Even though there are probably about 10,000 different lamps available from the major manufacturers, there are really only two "types" of lamps used for general lighting. In a filament lamp, light is emitted by a tungsten wire which gets hot from electricity passing through it. A halogen lamp is a filament lamp with a halogen gas in it. This allows the filament to burn hotter and more efficiently while putting out a whiter light. Halogen lamps also last longer than regular incandescent lampsIn a gas discharge lamp light is emitted directly by atoms in the gas through which an electric “spark” is occurring. A gas discharge lamp is like a controlled bolt of lightning that goes on and on. The ballast regulates the discharge and ensures that the current does not stop after an electric charge “discharges” itself. Gas discharge lamps are much more efficient than filament lamps, but they require a ballast to operate them: they cannot be directly plugged into the electrical line. Fluorescent lamps are considered low intensity discharges while high intensity discharge lamps include mercury vapor, metal halide and high pressure sodium lamps.   Mercury vapor lamps have been used commercially since the 1930’s. High pressure sodium lamps and metal halide lamps were both invented in the 1960’s. Metal halide lamps are mercury lamps to which a small quantity of chemical salts has been added. This almost doubles the light output and improves the color rendering. Metal halide lamps give a crisp, white light and are used to light sports stadiums, malls, industrial areas, car lots, and so on. High pressure sodium lamps provide an efficient golden light and are popular in street lighting.   Lighting Fixtures   Fixtures house the lamps and help distribute the light. Lighting professionals call the light bulb a “lamp” and they call the table lamp a “luminaire.”While the lamp is the primary source of light, the luminaire uses reflectors and lenses to help spread the light out and put the light where it is needed. Most fixtures for fluorescent and HID (high intensity discharge) lamps also contain the ballast. In compact fluorescent lamps the ballast is often a small electronic module attached to he base of the lamp. 

The qualitative aspect has to do with ensuring that the space has a pleasing feel and ambiance. It is the artistic interspersing of light and shadow, of illumination and darkness, of figure and form.The quantitative aspect revolves around making sure that there is adequate light for the task at hand. The Illuminating Engineering Society (IES) of North America publishes guidelines for light levels for many many tasks and activities based on the nature of the task, the size of objects handled, the detail required, the average age of the people in that space and so on. A typical office is lit to an illumination of 30 to 100 “footcandles”. Light levels can also be expressed in the metric unit "lux"; 1 footcandle is approximately 10 lux.The rate of energy consumption is called “power” and is measured in watts. A 200 watt lamp is consuming energy at twice the rate of a 100 watt lamp. The electric company charges consumers for the total amount of energy they consume. This is measured in kilowatt-hours or kwh. A 200 watt lamp burning for 5 hours consumes 1,000 watt-hours of energy, which is called a kilowatt-hour. Note that burning a thousand watt lamp for one hour costs the same as burning a hundred watt lamp for ten hours.on the average, electricity costs about 10 cents per kilowatt hour. It is as high as 20 cents per kwh in some places and as low as 5 cents in others.A 100 watt lamp burning for 10 hours is 1 kwh which costs 10 cents (average), that is it costs a penny an hour. Electric lighting is one of the best values you can get for your penny!