Lighting

About Lighting

Lighting accounts for 15% of power consumption of the typical American household. 

The two most common types of lighting are Incandescent and Fluorescent. Incandescent lights are descendents of Thomas Edison's original light bulb. They are used in table and floor lamps, downlighting, and outdoor fixtures. They come in a variety of wattages for varying levels of light intensity. 

When energized, incandescent bulbs produce a yellow colored light. Colors on objects seen under an incandescent light are considered to be "true".

Incandescent performance characteristics are as follows:

      Wattage         Lumens*          Life (hours)

40

445

1500

60

870

1000

75

1180

750

100

1710

750

* Lumen, or luminous flux, is the unit of measure for light intensity

Fluorescent lamps come in the familiar straight and circular tube form, and are now also available as compact bulbs. Compared to incandescents, fluorescent lights have higher energy efficiency and emit light that is described as "bluer", "cooler", and "white". 

Fluorescent fixtures with electromagnetic ballasts have a visual flicker, are slow to start up, and develop a humming noise over time.  With the introduction of electronic ballasts, these problems have gone away, increasing the marketplace acceptance of fluorescent lighting. 

Fluorescent performance characteristics are as follows:

       Wattage            Lumens*            Life (years)

40

3000

13

34

2700

13

32

2950

13

An incandescent light bulb consists of a tungsten filament enclosed in an evacuated space. The filament essentially acts as a resistor for the electrical current applied to it. As the filament heats up, it glows, thus providing useful light. The frosting on the inside to bulb serves to diffuse the light radiating from the filament.

A fluorescent tube or "lamp" consists of a long thin glass tube filled with low pressure mercury vapor. As an electrical charge is applied to the tube, the conducting mercury vapor emits UV waves. As these waves pass through the phospor coating on the inside of the tube, they convert to visible light.

To provide the proper kind of electrical charge to a fluorescent tube, a ballast is required. In general, the higher the output frequency of the ballast, the higher the efficiency of the tube in operation. For this reason, high frequency (25-35kHz) electronic ballasts, outperform the low frequency (<15kHz) electromagnetic ballasts.

If you touch an incandescent bulb when it is on, you will burn your fingertip. If the do the same with a fluorescent tube, it will feel warm, but not burning hot. Relative coolness to the touch indicates the higher energy efficiency of the fluorescent. For the same lighting level, fluorescent will use 70-75% less electrical energy.

Lighting color is measured on two different scales: temperature and color rendering index (CRI). Temperature measures in degrees Kelvin. Lower temperature light (2000-3000K) gives objects a warm red color, while higher temperature (4000-7000K) light projects a cool blue-green hue. The median temperature of 3500K compares to the noonday sun, which is the benchmark of color "trueness".

The Color Rendering Index (CRI) measures color contrast. Its scale runs from 0-100. Incandescent and Halogen bulbs generally have a CRI close to 100. The closer to 100 the CRI measures, the "truer" the colors will appear.

Consider where you want to see true colors at home. Your clothes closet, living areas, kitchen, and baths are likely candidates. Do you want the clothes that you put on this morning to look different when you go outside?

Seeing color trueness may not be as important in the garage, hallways, basement, or your home office. However, today's technology allows you to have fluorescent light that produces a truer light. Color-corrected fluorescents cost slightly more, but provide almost the same color light as incandescents.

One disadvantage commonly associated with fluorescent lighting is the humming noise that older fixtures emit. Humming occurs only with magnetic ballasts. Newer electronic ballasts operating at much higher frequencies, do not hum or do so minimally.

  

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About Lighting

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