Incandescent Bulbs
Compact Fluorescent Lamps
Halogen Bulbs
Fluorescent Lamps
Measuring Light Output and Usage
Comparison of Typical Bulbs

Recent studies reveal that over 20% of the nation’s electricity consumption is absorbed into various types of lighting products and systems. Currently, a majority of America’s electric lighting depends on either incandescent bulbs or fluorescent electric lamps for illumination. Within the commercial sector, the potential impact of advanced lighting technologies upon energy conservation is great.

Although most lights in commercial buildings are fluorescent, incandescent light bulbs serve about 20% of commercial lighted floor space and account for nearly 40% of commercial energy use.

Incandescent Bulbs
An incandescent lamp harnesses light from a heated material. Electric current flows through a thin tungsten wire (the filament) and heats the filament to about 3000°C, which causes heat and light to emit. The bulky globe or shell is under a vacuum, forming a heat insulator to keep the bulb and socket from getting too hot. The filament also produces infrared (heat) radiation, some of which is absorbed by the glass bulb wall as it passes, contributing more heat to the bulb. In addition, an inert gas is inside the bulb to prevent the filament from burning out. Incandescent bulbs are now considered the least energy-efficient light source, but are still considered the traditional format of electric lighting. Incandescent bulbs dissipate a lot of the electricity they use as heat to accompany the light emitted from its glowing filament.

EnergyMiser, or Supersaver bulbs are incandescents that use 5% to 13% less electricity than ordinary light bulbs with only a very minimal reduction in light output. They cost slightly more, but are economical on a lifetime basis. Don’t confuse these with Longlife bulbs, which can last up to twice as long, but are less efficient than standard bulbs. Longlife bulbs are generally recommended in locations where it is difficult to replace bulbs. Facts about incandescent bulbs:

• The potential life is maximized to 1,000 hours of operation and 22 lumens of light output per watt.
• They are relatively inexpensive ($.60 to $1), convenient to install, and readily available.
• 10% of its energy is emitted in the form of light.
• Incandescents have the highest color rendition index (CRI). The CRI measures how accurately a light source represents an object’s color compared to an ideal source like the sun. Incandescents have a CRI of 100.

Facts about compact fluorescent lamps:

• The average compact fluorescent bulb lasts 8 to 10 times longer than any incandescent bulb.
• By switching from incandescent lighting to compact fluorescent lighting the average consumer can save 50 to 80% in energy costs with minimal loss in lighting quality.
• Pricing for these products can range from $6 to $15 each.

Halogen Bulbs
A halogen lamp is an incandescent bulb with a halogen gas added to reduce evaporation. Halogen lamps run at a higher temperature, providing a whiter light and greater efficiency. Widely used for display, accent lighting, halls, and lobbies, halogen lamps are used in many of the more modern lighting fixtures. Halogen bulbs are more efficient than standard incandescent bulbs and last three to four times as long. Replacing incandescent track and spot lighting is the best application for halogen bulbs; you can use a lower wattage bulb and get the same general effect as with larger wattage incandescents. This also holds true for outside floodlights. However, be wary of high wattage halogen lamps, sometimes in the 300 to 500 watt range. These produce a tremendous amount of light but consume an equally large amount of energy. You should also be aware that there are serious safety concerns over very popular halogen torchiere-style floor lamps. These fixtures generate intense heat and can cause fires if placed too close to flammable materials. Other types of today's popular lamps are described as follows:

Low-pressure sodium -- This light source converts nearly 35% of the energy consumed into light. Low-pressure sodium bulbs should last at least 10,000 hours and deliver as much light at the end of their life as in the beginning. However, they are the most expensive lighting source. They are also the largest, and hence, most difficult to control in terms of light distribution. In addition, because of their singular yellow color, they have very low color rendition index (CRI). Objects under low-pressure sodium illumination appear yellow, gray, or black.

High-intensity discharge (HID) -- These light sources are the elite, energy-efficient lighting devices on the market today for outdoor illumination. Each of these lamps requires a specially designed ballast and has a high initial cost. However, their lower operating cost rapidly returns the initial investment. High-intensity discharge lamps have one potential drawback that may limit their use - a start-up delay from 1 to 7 minutes from the time they are switched on until they fully illuminate. There are two particular types:

• Metal halide lamps -- Metal halide lamps have the best CRI of the high-intensity discharge lamps. They are sometimes used for commercial interior lighting because of their excellent color and are the preferred light source for stadiums where there are television broadcasts. They are more efficient than mercury vapor lamps while having the same light output.
• High-pressure sodium lamps - High-pressure sodium lamps produce a golden white color that tends to blacken red and blue objects. Because their CRI is about 25, these lamps are rarely used for interior commercial lighting. They are used more frequently for interior industrial applications, such as in warehouses and manufacturing. Their small size and excellent efficiency make them the most popular choice for street and area lighting.

Facts about HID lamps:

• HID luminaries can have lamps that range from as low as 35 watts up to 1,000 or more watts, with lamp lumen output ranging from 1400 to 140,000 or more.
• Pricing for these products can range from less than $100 per unit with lamp, to over $400, depending on options, ballast selection, and quantity.

Fluorescent Lamps
A fluorescent lamp is a low-pressure mercury vapor lamp confined in a glass tube, which is coated on the inside with a fluorescent material known as phosphor. The energized filament delivers electrons to the ionized inert gas within (usually argon), forming a plasma that conducts electricity. The ballast limits the flow of the current through the tube. Consequently, the plasma excites the mercury vapor atoms which then emits a spectra of red, green, blue, and ultraviolet lights. The internal phosphor coating then converts the ultraviolet light into other colors. Facts about fluorescent lamps:

• The minimum acceptable CRI for most indoor commercial applications is 70, but levels above 80 are recommended.
• On average, 40 watts of energy in a fluorescent tube produces as much light as a 150-watt incandescent bulb.
• Compared to traditional incandescent bulbs, less heat is generated from the filament at similar lighting output.
• Pricing for fluorescent lamps can range from under $50 per unit with lamp, to $300 or more, depending on options, ballast selection, and quantity.

Measuring Light Output and Usage
Most people readily associate the term wattage with lights, but mistakenly assume it is a measure of the amount of light produced. Wattage is actually a measure of the energy usage of the bulb. The light output of a bulb is measured in lumens. A bulb with a lower wattage can actually have a much higher lumen output. Lighting packaging today must indicate the lumens produced by a bulb.

Improving the efficiency of a bulb requires using less energy (watts) for a given level of light output (lumens). A common measure of the efficiency of a bulb, termed efficacy, is lumens divided by watts. The cost-effectiveness of a bulb also takes into account its cost and life. A comparison of typical bulbs appears below. Be aware that these are representative only; there are variances among specific bulbs, and other factors, including light fixtures, bulb placement, and age of bulb, will effect actual light output.

Comparison of Typical Bulbs

Notice, for example, that a 52-watt Energy Miser bulb uses about 13% less energy than its 60-watt incandescent counterpart, but in turn produces over 90% of the light. A comparable long life bulb, however, while lasting 2.5 times as long, will only produce about 82% of the light of the incandescent. On the other hand, a 13-watt Compact Fluorescent produces the same light as the 52-watt Energy Miser but uses only 25% of the energy and lasts 10 times as long. Even given its higher cost, such a bulb would cost approximately $28 dollars over its life vs. $72.50 for an incandescent (using a cost per kWh of 10 cents).

Light quality is measured in Color Rendering Index (CRI) and Correlated Color Temperature (CCT). CCT, which is measured on the Kelvin (deg.K) temperature scale, provides an indication of how the light will look. Cooler lights (those with more blue) are those with higher temperatures; a CCT higher than 2,800 typically indicates a cooler light and will look whiter than a standard incandescent. Bulbs with CCTs below 2800 will appear more red in nature.

CRI is a measure of how objects will look under the light. It is roughly a comparison of the light source with natural light, with a CRI of 100 the equivalent of natural light. CRI for a standard incandescent is 100. Older fluorescents will typically have a CRI in the 60’s.

Source: US DOE FEMP "Types of Lighting"