Too often, lighting retrofits start and finish with the objective of pairing lamps with ballasts to turn electricity into visible light most efficiently. While the majority of energy savings potential often resides here, pursuit of high efficiency alone may lead to compromises in light quality and controllability and higher system installation and maintenance costs. Lamp and ballast specification should seek to optimize efficiency while maintaining a balance with these other considerations.

While a wide range of light sources are available, the predominant types used in commercial and industrial spaces are fluorescent and high-intensity discharge (HID). Historically, fluorescent lighting has been used for high-quality, general-purpose indoor diffuse lighting. HID has been used for industrial and outside lighting. However, technical advances and a flood of new products have increased the use of HID in interiors.

Although fluorescent sources are still limited by their inability to function in very hot or cold environments or as spotlights, advances in physical size, thermal performance, and light quality are allowing wider application in industrial, manufacturing, and residential environments. Likewise, in the past, HIDs have typically been limited by their high light output and their inability to render color accurately or to be switched on and off frequently or dimmed. Today, however, HID lamps are used indoors in some applications where light quality is critical and where dimming and lower light outputs are necessary. While practical limitations still exist, now, more than ever, specifiers need to research lamp capabilities and understand the tradeoffs between efficiency and performance. For example, linear T5 lamps, which have recently been introduced, are becoming popular in direct/indirect pendent mounted systems, cove lighting and retail display lighting. But should not be used in retrofit applications because of the following limitations:

• Available only in metric lengths
• Lamp holder design is different that T8 and T12
• Higher tube luminance, which will cause glare problems in existing lighting equipment.

Ballast selection is integral to lamp performance. All fluorescent and HID lamps require a ballast to provide the necessary starting voltage and regulate lamp current and power quality. Ballasts determine the lamp’s light output, life, and control capabilities. Similar to advances in lamp technology, electronics advances have greatly expanded ballast capabilities and selection.

The three types of fluorescent ballasts are magnetic, electronic, and hybrid ballasts. Magnetic ballasts, also known as electromagnetic ballasts, have improved from the standard-efficiency, core-coil ballasts last made in 1989 to higher efficiency models. Electronic ballasts have been developed for almost all fluorescent lighting applications to replace their conventional magnetic counterparts directly. Electronic ballasts operate fluorescent lamps at a higher frequency, which improves system efficiency by about 30 percent when used in conjunction with T8 lamps to replace T12 lamps and standard magnetic ballasts. Electronic ballasts also offer these advantages:

• Less audible noise and virtually no lamp flicker.
• Dimming capability (with specific ballast models).
• Ability to power up to four lamps, increasing energy efficiency by an additional 8 percent, while reducing first cost and maintenance costs.

Hybrid ballasts, which combine features of magnetic and electronic ballasts, are also available. Although these ballasts offer the same efficiency benefits as electronic ballasts, they cannot power more than three lamps.

Instant-start circuitry offers an additional 5 percent efficiency compared with rapid-start electronic ballasts. However, if lamps are frequently switched on and off, additional lamp and maintenance costs may exceed energy savings.

Programmed-start ballasts offer increased lamp life compared to instant or rapid start ballasts. Programmed-start ballasts are designed to soft start the lamp, which decreases lamp cathode damage. luminaires are switched on and off frequently, such as in spaces controlled by an occupancy sensor.

Selecting ballasts for HID lamps involves matching a ballast type to the electrical distribution system in your building to control the lamp light output when line voltage varies. The level of this control is then balanced against ballast losses, power factor, lamp life, and cost. lamps, these ballasts are becoming more popular because of their smaller size, weight, decreased lamp color shifting, and increased compatibility with lighting controls Nominal efficiency improvements of only 5 to 7 percent make retrofits difficult to justify on energy savings alone. Linear reactor circuit ballasts have been developed which, when used with matched, pulse-start, metal halide lamps, can cut ballast losses in half and offer a 20-percent improvement in efficiency.