Types of Lamps
There are literally thousands of different types of lamps available, each with very unique characteristics and purposes. The chart below shows, generally, the types of bulbs used in shop and industrial settings. Each group has varying efficiencies, operating ranges and life expectancies.
Lamp efficiency (brightness and economy) is expressed as a ratio of total luminous flux (light quantity) generated from the light source to the lamp wattage consumed to generate it.
Lamp efficiency / unit : lm / W (lumen / watt)
For example, the lamp efficiency of a 40W fluorescent lamp with a total luminous flux of 3,100 lm
3,100 / 40 = 77.5 (lm / W).
Categories of Lamps and their Attributes:
|Lamp||Incandescent||Fluorescent||High-Intensity Discharge (HID)|
|Life Span||750 to 2,500 hours||Frequent starts and stops reduce life span. Ballast life 15 to 20 years.||5,00 to 20,000 hours. Reduced by frequent starts and stops. (Over 24,000 hours for high-pressure sodium.)|
|Operating Temp.||Operates well at any temperature||Lamps designed for specified operating ranges. Generally have problems with low-temperature operation. Indoor-use fixtures have ballasts that trip at coil temperatures above 105°C.||Any temperature range|
|Spectral Power||Strongest in red emissions. Weakest in blue emissions.||Available in any given spectral range. CRI values as high as 98.||Strongest in blue and green emission. Generally emitting pale light. (Yellow and white light with high CRI for high-pressure sodium.)|
|General||3 to 10,000 Watt ranges available||Available in anything from 115 to 16,500 lumens. Over 40 different Wattages available in standard sizes.||Physically small compared to other types of fixtures. Low Wattage and low efficacy. Shut off with power interruptions and will not start until sufficiently cooled.|
Incandescent lamps have a standard life span ranging from 750 to 2,500 hours. They operate well at any temperature. Only small portions of their emissions radiate in the visible spectrum of light. Their greatest region of radiation is in the infrared region. In the visible spectrum, incandescent lamps radiate in the red region. These lamps have a very weak blue emission. The highest efficacy standard incandescent lamp available is the 10,000-W studio lamp rated at 33.5 L per W with a 75-hour life span. In contrast the 3-W indicator lamp has a 3,000-hour life and an efficacy of 4 L per W.
Fluorescent lamps are the most versatile of any style of light available. They typically range from 155 L to 16,500 with over 40 different wattages in standard sizes. When operating these lamps a negative electrical resistance characteristic is experienced, which means that as current increases the lamp’s resistance to current decreases. A ballast is thus required to limit the lamp’s current and protect it from destroying itself. Ballasts used in indoor settings contain thermal protection switches. The switches open when the internal coil temperature exceeds 105°C. These are known as “Class P” ballasts and are required by N.E.C. code when used indoors. Regular on/off cycling of lamps is an indicator of ballast failure. The Certified Ballast Manufacturers Association (CBM) has established standards for ballast performance. Well-ventilated ballasts can expect a life of 15 to 20 years. The ballast also acts as a transformer. Though a lamp may be rated for a particular voltage and wattage, such as 101 or 29 V, it may actually be powered by 120 or 277 V through the ballast. Lamp life is better for lamps that are used over lengthy periods with few starts and stops as opposed to those used with frequent starts and stops over short periods. Each fluorescent lamp is designed for use at a specific temperature range. Most commonly, this is ambient temperature. Typically, fluorescent fixtures are available in any given visible spectral range. These lamps can be as high as 98 CRI for tough color applications.
High-Intensity Discharge (HID)
High-intensity discharge lamps are physically smaller than the preceding types of lights. Three types of HID lamps are commonly used industrially:
- Mercury vapor
- Metal halide
- High-pressure sodium
Mercury vapor lamps are low wattage and generally inefficient when compared to other lamps. Mercury and metal halide lamps also produce ultraviolet radiation when operating. Because of this their outer bulbs are constructed of borosilicate glass, which can shield the ultraviolet radiation. Mercury vapor and metal halide lamps are strong spectrally in the blue and green regions generally emitting pale light.
Metal halide lights can be constructed with good color-rendering ability. Their average useful life is 5,000 to 20,000 hours but reduces significantly with frequent starts and stops.
High pressure sodium lamps average a life of over 24,000 hours. They generally produce a yellowing light. There are sodium lamps with CRIs in the 80s that can produce a white light similar to some incandescent sources. High-pressure sodium lamps sport low operating costs and high efficacy.
HID lamps share the negative resistance characteristic experienced with fluorescent lamps. Ballasts are required to regulate their internal power. HID lamps also experience stroboscopic effects. When supplied by a 60 Hz source, HID lamps will cycle on and off 120 times per second. An object rotating at speeds that are multiples of 60 Hz will appear motionless when viewed under these lamps. Using three-phase power and alternating the phases used can minimize this stroboscopic effect by adjacent lamps. HID lamps shut off when there is even momentary power interruption. The lamps will not restart until they have cooled sufficiently.