Encyclopedia of Color Science and Technology

2016 Edition
| Editors: Ming Ronnier Luo

Tubular and Compact Fluorescent Lamp

Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-8071-7_124

Synonyms

Definition

Lamp that produces light as a result of an electrical discharge, generated between two electrodes, in a low-pressure mercury vapor that is contained in a transparent tube whose inside is coated with fluorescent powder that converts the ultraviolet part of the emitted radiation from the discharge in visible light.

Types of Tubular Fluorescent Lamps

Fluorescent lamps belong to the family of low-pressure mercury gas discharge lamps. They are by far the most widespread discharge lamp types. They are available in both tubular and compact versions. Although the operating principle of compact fluorescent lamps is largely the same as that of the tubular version, their construction and performance are in many ways different from that of the tubular version [2, 3].

Working Principle

The discharge tube of a fluorescent lamp is filled with an inert gas and a little mercury and has an electrode sealed into each end (Fig. 1). To facilitate starting, the electrodes of most fluorescent lamps are preheated prior to ignition, which is accomplished by means of a high-voltage pulse, generated by an external device called the igniter or starter. (Igniters are available as simple glow-switch starters or as electronic devices.) When the lamp is switched on, the electrodes begin emitting electrons, and through the collision of these electrons with the gas atoms, the ionization process starts. The inert gas is then heated up and the mercury inside the lamp is completely evaporated to give a mercury vapor pressure of about 0.8 Pa (8.10−6 atm). The emitted electrons collide with and excite the mercury atoms, resulting in the emission of ultraviolet radiation and a small amount of blue visible light. The inside of the discharge tube is coated with a mixture of fluorescent powders. The ultraviolet radiation is converted to visible light when it passes through the fluorescent powder coating.
Tubular and Compact Fluorescent Lamp, Fig. 1

Main parts and principle of operation of a tubular fluorescent gas discharge lamp (TL) [1]

Like almost all gas discharge lamps, a fluorescent lamp cannot be operated without some device to limit the current flowing through it. This device, usually in the form of an inductive coil, is called a ballast. Fluorescent lamps also need, again like most discharge lamps, an igniter for starting the lamp.

Tubular Fluorescent Lamps

Tubular fluorescent lamps are widely used in offices, schools, shops, and low-ceilinged industrial premises. So today their use is mainly indoors.

Materials and Construction

The main parts of a tubular fluorescent lamp are (see Fig. 1):
  • Glass tube

  • Fill gas

  • Electrodes

  • Fluorescent powder

Glass Tube

The tube of a normal fluorescent lamp is made of glass that is doped with a special material that blocks that UV radiation from the mercury discharge that is not converted by the fluorescent powder into visible light.

The original fluorescent lamp had a diameter of 38 mm. This tube diameter is usually characterized as T12, where the 12 stands for 12 times one-eighth of an inch (Table 1). This type of fluorescent tube is seldom seen today. During the late 1980s, a smaller and more efficient version was introduced that has a diameter of 26 mm. Today an even thinner and more efficient version has become the standard: the TL5 with a diameter of 16 mm. Even thinner fluorescent lamps are produced, but these are not for use in general lighting.
Tubular and Compact Fluorescent Lamp, Table 1

Fluorescent lamps with different tube diameters and their designations

Tube type

Diameter (inch)

Diameter (mm)

T12

12 * 1/8

38

T8

8 * 1/8

26

T5

5 * 1/8

16

T2

2 * 1/8

6

T1

1 * 1/8

2.8

Fill Gas

The gas filling in a fluorescent lamp consists of a mixture of mercury vapor and an inert gas. The inert gas has three functions:
  • To facilitate ignition, especially at lower temperatures

  • To control the speed of the free electrons

  • To prolong the life of the electrodes by reducing evaporation of electrode material

The inert gas usually consists of a mixture of argon and neon, although sometimes krypton is used as well.

Electrodes

The function of the electrodes is to provide free-running electrons, which are necessary to start and maintain the discharge. A fluorescent lamp electrode consists basically of a tungsten filament (Fig. 2) that is coated with the so-called emitter material to facilitate electron emission.
Tubular and Compact Fluorescent Lamp, Fig. 2

Triple-coiled filament electrode [1]

Fluorescent Powder

The small crystals of the fluorescent powder applied to the inside of the discharge tube absorb the UV mercury radiation and convert it into visible light (this physical phenomenon is called luminescence). Different fluorescent powders convert the ultraviolet radiation into visible light of different wavelengths and thus different colors (Fig. 3).
Tubular and Compact Fluorescent Lamp, Fig. 3

Different types of fluorescent powder. Left, under white light, and right, the same fluorescent powders under UV radiation [1]

By mixing different fluorescent powders in different proportions, lamps producing different tints of white light can be made. The type and composition of the fluorescent powder is the most important factor determining the light characteristics of a fluorescent lamp, such as color temperature, color-rendering index (Ra), and to a large extent the luminous efficacy of the lamp (lm/W). Some fluorescent powders convert the ultraviolet radiation into wavelengths covering almost the whole visible spectrum. Such powders therefore produce white light when used alone. However, their color rendering and efficacy are poor (Ra < 70 and lm/W < 80). Because these powders lose some of their conversion activity relatively quickly, lamp-lumen depreciation is relatively large. Nowadays these lamps are hardly ever produced. Today fluorescent lamps often employ a mixture of three fluorescent powders, each having a very narrow spectrum band in red, green, and blue. In this way, white light is again obtained, but of better color rendering and efficacy (Ra > 80, lm/W up to 105). The lamp-lumen depreciation with these powders is very low (<10 %). For cases where extremely good color rendering is required, a mixture of more than three powders is used, resulting in lamps with excellent color rendering (Ra > 90), very low lumen depreciation, and high luminous efficacy (slightly smaller than the previous version, viz., up to some 90 lm/W).

Properties

Energy Balance

Just below 30 % of the input power is converted into visible radiation and a very small part into UV radiation. The rest is lost in the form of heat (at the electrodes, in the discharge itself and as infrared radiation). Compare the figure of 30 % with 8 and 12 % for incandescent and halogen lamps, respectively.

System Luminous Efficacy

As with most lamps, the luminous efficacy of tubular fluorescent lamps is dependent on the wattage of the lamp and the color quality of the light it gives. Types with color rendering better than Ra 80 and with low lumen packages have a system luminous efficacy starting at 50 lm/W, while lamps with higher lumen packages reach efficacies up to some 105 lm/W. Lamps with extremely good color rendering (Ra > 90) have 15 % lower efficacies.

Lumen-Package Range

Common tubular fluorescent lamps are produced in the range from some 500–6,000 lm (corresponding wattage range approximately 8–80 W). Special very-high-output lamps are also produced in versions up to some 9,000 lm (120 W).

Color Characteristics

As has been mentioned, by mixing different fluorescent powders in different proportions, lamps with different spectra can be produced. As with all gas discharge lamps, the spectrum is discontinuous. Figures 4, 5, and 6 show the spectra of fluorescent lamps with different color temperatures Tk and color-rendering index Ra.
Tubular and Compact Fluorescent Lamp, Fig. 4

Spectral energy distribution of a fluorescent lamp colortype 827: Tk 2,700 K and Ra 80 [1]

Tubular and Compact Fluorescent Lamp, Fig. 5

Spectral energy distribution of a fluorescent lamp colortype 840: Tk 4,000 K and Ra 80 [1]

Tubular and Compact Fluorescent Lamp, Fig. 6

Spectral energy distribution of a fluorescent lamp colortype 940: Tk 4,000 K and Ra 90 [1]

The colortype designation used for fluorescent lamps is standardized, with the first digit standing for the color-rendering index Ra and the last two digits for the color temperature Tk. Thus, the colortype 840 stands for a color-rendering index value Ra in the 80-ties and a color temperature of around 4,000 K.

Present-day quality fluorescent lamps are produced in a whole range of color temperatures varying from 2,700 K (warm-white or incandescent lamp color tint) to 6,000 K (bluish white), most of them in two color-rendering qualities with Ra in the 80-ties (800 series) and 90-ties (900 series), respectively. For special applications, versions are produced with extremely high color temperatures (up to some 17,000 K) with color rendering in the 80-ties. Today, fewer and fewer of those fluorescent lamps with poor color-rendering qualities (viz., Ra around 65 or less) that were produced in the past are produced.

Lamp Life

During the operation of a lamp, the electrodes lose emitter material due to evaporation and as a result of the bombardment with ions from the discharge. This is the main cause of final lamp failure: the lamp will no longer start, due to a broken electrode, or else it flickers because insufficient emitter material remains. The lifetime of fluorescent lamps and gas discharge lamps in general is thus very much dependent on the construction and materials of the electrodes. Conditions that influence lifetime are principally the type of gear used, the switching frequency, and the ambient temperature. The switching frequency plays a role because the high-voltage peak needed for ignition causes the electrodes to lose some of their material (sputtering). The more accurately the igniter-ballast combination preheats the electrodes, the less severe this effect is. The occurrence of such things as shocks or vibrations, different burning positions, and supply-power variations can play an additional role.

Today’s high-quality fluorescent tubes have economic lifetimes (based on 20 % mortality) of 15,000 h to more than 20,000 h if used on a so-called high-frequency or HF ballast and around 12,000 h when used on an electromagnetic ballast. For situations where the actions needed to replace lamps are expensive, special, more expensive, long-life fluorescent lamp versions are available with lifetimes ranging from some 40,000–65,000 h. This long life is obtained by means of a special electrode design and construction.

Lamp-Lumen Depreciation

The main cause of lamp-lumen depreciation in a fluorescent lamp is that the fluorescent powder slowly becomes less active as a result of chemical attack by mercury ions. There may also be some blackening of the tube wall from the electrodes. For cool-white and cool-daylight lamp types, the lumen depreciation is higher than for lamps with a warmer tint. This is because of the faster depreciation of the blue fluorescent powders. Lamp-lumen depreciation for present-day high-quality fluorescent tubes is around 10 % after some 20,000 h.

Run-Up and Reignition

Fluorescent lamps operated on present-day electronic control gear start very quickly (within 1.5 s) and without flickering. This last is in contrast to lamps used on the older, glow-switch starters. After ignition, the light output increases quickly up to its maximum in about 1 min. When a fluorescent lamp is switched off, the vapor pressure drops so quickly that reignition is instantaneous.

Switching

It has already been mentioned that the switching frequency has an influence on lifetime, the influence being dependent on the type of electrical control gear used. Lamps operated with HF electronic-preheat-start ballasts show in general little sensitivity to the switching cycle. This is because of the well-controlled starting conditions of the lamp (warm start). HF non-preheat starting leads to a relatively short lamp life under frequent-switching conditions.

Dimming

Dimming of modern fluorescent lamps on high-frequency electronic ballasts down to 3 % of the nominal light-output value is easy, possible with an additional circuit that changes the operating frequency.

Ambient-Temperature Sensitivity

The luminous flux of a fluorescent lamp is determined by the mercury vapor pressure during operation. The mercury vapor pressure is in turn determined by the coldest spot in the tube, normally the tube wall, which of course is also dependent on the ambient temperature. The consequence of this is that the light output of fluorescent lamps is dependent on ambient temperature. The lumen output of fluorescent lamps is generally published for an ambient temperature of 25 °C. T12 and T8 lamps have their maximum light output at 25 °C, while the smaller diameter T5 lamps give their maximum light output at 35 °C (Fig. 7). To obtain a high and near-constant light output over a wide temperature range, the mercury in some fluorescent lamp types is introduced into the tube not as a pure metal but as an amalgam. Such lamps have a lumen output that is near constant over the temperature range of 25–65 °C.
Tubular and Compact Fluorescent Lamp, Fig. 7

Relative light output of a T8 and a T5 fluorescent lamp in relation to the lamp ambient temperature [1]

Mains-Voltage Variations

If the mains voltage varies, the power consumed by the lamp changes and with it the vapor pressure and consequently the lumen output. Given an optimized lamp/electromagnetic ballast combination, a 10 % deviation in power will keep the lumen-output decrease usually at less than 10 %. On high-quality high-frequency electronic ballasts, a 10 % deviation in power can keep the lumen-output decrease at less than 3 %. In all cases, with higher mains-voltage decreases, the lumen output decreases rapidly.

Product Range

Tubular fluorescent lamps are being produced in a wide variety of types with different properties. The more important lamp types are listed in Table 2.
Tubular and Compact Fluorescent Lamp, Table 2

Different tubular fluorescent lamp types

Lamp aspect

Range

Tube diameter

38 mm (T12)/26 mm (T8)/16 mm (T5)

Lamp circuit

Electromagnetic/HF electronic

Balance efficacy/lm output

High efficacy (HE)/high output (HO)/very-high output (VO)

Color temperature Tk

Standard range (2,700–6,000 K)/8,000–17,000 K

Color rendering Ra

Ra > 90 (900 series)/80 < Ra < 90 (800 series)/Ra < 80

Color

Red, green, blue, etc.

Lifetime

Standard (up to 20,000 h)/very long (up to 65,000 h)

Ignition method

Standard/low temperature ignition

Tube coating

No coating/coating (silicon, protective, or reflector)

Safety of operation

Standard/explosion safe

Tube length

Standard (450–1,800 mm)/mini (150–500 mm)

Tube shape

Tubular/U-shaped/circular

Up until 1990, fluorescent tubes were operated on electromagnetic ballasts. Even today, this way of operating a fluorescent tube is called “conventional,” although operation on high-frequency or HF electronic ballasts has since become the standard. T5 lamps can only be operated on HF electronic gear.

T5 lamps are produced in an execution where the design is such that the maximum luminous efficacy is obtained: the high efficiency, HE, series of lamps. Another type of execution is optimized for maximum lumen output at the cost of efficacy: the high output, HO, series (10 % higher lumen output and 10 % lower efficacy). Very-high-output lamps (VHO) are produced as well.

Some tubular fluorescent lamps are given a coating on the outside of the tube. A silicone water-repellent coating is applied to prevent starting problems for types that are used under conditions of high humidity. Types intended for use in food stores can be given a special protective coating that prevents surrounding products from contamination in the event of accidental lamp breakage. Some of these latter types have a spectrum that makes the appearance of food more appealing (especially meat). In reflector fluorescent lamps, a diffuse reflective coating is applied between the upper part of the inner tube wall and the fluorescent powder. The light is concentrated through the uncoated area (or “window”) of the lamp, so increasing the downward component of the light (Fig. 8).
Tubular and Compact Fluorescent Lamp, Fig. 8

Reflector fluorescent lamp

Compact Fluorescent Lamps

Compact fluorescent lamps (CFLs) were originally developed (beginning of the 1980s) for use in those applications where incandescent lamps were traditionally used. Today, the application of compact fluorescent lamps has been widened and includes not only domestic lighting but office and road lighting (residential streets) as well. For the more compact versions, alternatives in the form of solid-state lamps are becoming increasingly more available.

Working Principle

The gas discharge principle employed in compact fluorescent lamps is exactly the same as that in tubular gas discharge lamps (see previous section). Their compactness is achieved by reducing their length. This is done either by folding a longer tube into a shorter one or by joining together two or more parallel tubes so that one open pathway is obtained where free electrons and ions can move from one electrode to the other, as in a normal straight fluorescent tube (Fig. 9). The folding can be repeated or the interconnection can be done with more than two parallel tubes (always keeping one open pathway) to further increase the size of the lamp.
Tubular and Compact Fluorescent Lamp, Fig. 9

Folding one tube (left) or connecting two separate tubes (right) to form a compact fluorescent lamp with one open pathway between the electrodes

Materials and Construction

As far as fill gas, electrodes, and fluorescent powders are concerned, compact fluorescent lamps are essentially the same as conventional tubular fluorescent lamps. Reference is therefore made to the previous section “Tubular Fluorescent Lamps.”

The main difference in construction between compact and tubular fluorescent lamps lies in the tube shape and the lamp caps. But another point of difference is that in those compact lamps that need to work directly from the mains without any external electrical component, the igniter and ballast have to be integrated in the lamp itself. In this case, the lamp foot is used for housing the control gear.

Tube

A great variety of tube shapes are produced. Figure 10 shows versions where tubes are interconnected. All these are examples of compact fluorescent lamps where the gear is not integrated in the lamp itself (compact fluorescent lamps nonintegrated CFL-NI). Figure 11 shows a set of triple-folded types, while Fig. 12 shows two different folded, single-plane versions.
Tubular and Compact Fluorescent Lamp, Fig. 10

Nonintegrated two-leg compact fluorescent lamps. From left to right: two pins with bridge connection, two pins with bend connection, and four pins with bridge connection

Tubular and Compact Fluorescent Lamp, Fig. 11

Triple-folded nonintegrated compact fluorescent lamps

Tubular and Compact Fluorescent Lamp, Fig. 12

Single-plane-folded nonintegrated compact fluorescent lamps

Figure 13 shows examples of compact lamps where the gear (HF electronic) is integrated in the lamp foot (integrated CFL-I). Since these lamps can directly replace incandescent lamps, it is also desirable that their shape and dimensions should be very close to those of normal incandescent lamps. Figure 14 shows two retrofit versions where an outer bulb with an internal diffusing coating also ensures that the light distribution is close to that of an incandescent lamp.
Tubular and Compact Fluorescent Lamp, Fig. 13

Differently shaped integrated compact fluorescent lamps

Tubular and Compact Fluorescent Lamp, Fig. 14

Retrofit compact fluorescent lamps with shape, dimensions, and light distribution close to that of an incandescent lamp bulb

Lamp Cap

The compact fluorescent lamps with integrated control gear have the same lamp caps as normal incandescent lamps, viz., Edison screw type and bayonet caps.

In most nonintegrated, small, twin-tube versions, the starter is built into the lamp cap itself (integrated starter but nonintegrated ballast). All nonintegrated types are fitted with special caps. A large variety of caps and bases exist in order to ensure that only the correct type of lamp can be used in a given situation (especially defined by the type of gear used in the particular luminaire).

The lamp caps of nonintegrated compact fluorescent lamps are of the push-fit type (they fit by pushing them into the lamp holder). They are available in both square-shaped and rectangular-shaped versions. Lamp caps for lamps with an integrated starter employ two-pin connectors, while lamps for use with electronic control gear or dimmers have four-pin connectors (Fig. 10 right, Fig. 11 right, Fig. 12 right).

Properties

Energy Balance

Approximately 20 % of the input power of compact fluorescent lamps is emitted in the form of visible radiation. A tubular fluorescent lamp emits some 28 % of visible radiation. The difference is largely due to the fact that in compact lamps the multitude of closely packed tube parts absorb part of the light.

System Luminous Efficacy

The luminous efficacy of a compact fluorescent lamp is partly dependent on the wattage of the lamp and the color quality of the light emitted but more so on how and how many times the compact tube is folded. In low-wattage versions, good color-rendering versions have a system luminous efficacy starting at 45 lm/W, while higher-wattage versions reach efficacies of up to some 70 lm/W.

Lumen-Package Range

Compact fluorescent lamp with integrated control gear is produced in the range from some 250 to 2,000 lm (corresponding wattage range approx. 5–35 W). Nonintegrated types are available in the range from some 250 to 6,000 lm (corresponding wattage range approx. 5–80 W).

Color Characteristics

The color characteristics of compact fluorescent lamps are principally the same as those of normal fluorescent lamps. Reference on this point is therefore made to the previous section “Tubular Fluorescent Lamps.” The range of different color temperatures and color-rendering indices available with compact fluorescents is in practice somewhat limited compared to that found with the very wide range of tubular lamps.

Lamp Life

The lifetime of compact fluorescent lamps is very long compared with that of incandescent lamps, although it is usually shorter than that of tubular fluorescent lamps. Integrated versions (CFL-I) have, depending on type, a rated average lifetime of between 8,000 and more than 15,000 h. Note that the life of retrofit integrated CFLs is usually specified as rated average life (50 % mortality), as is the case with incandescent lamps (which have an average life of 1,000 h). Again, depending on type, nonintegrated versions (CFL-NI) have economic lifetimes (based on 20 % mortality) of 7,000–20,000 h.

Lamp-Lumen Depreciation

The lamp-lumen depreciation of compact fluorescent lamps is similar to that of tubular fluorescent lamps. See previous section “Tubular Fluorescent Lamps.”

Run-Up and Reignition

There are no fundamental differences here compared with normal fluorescent tubes. See previous section “Tubular Fluorescent Lamps.”

Switching

There are no fundamental differences here compared with normal fluorescent tubes. See previous section “Tubular Fluorescent Lamps.”

Dimming

Most integrated compact lamps are not dimmable. However, special, more expensive versions, with standard Edison or bayonet cap, are produced that can be dimmed to approximately 5 % of full light output. Dimming of nonintegrated, four-pin, compact lamps is possible and is fundamentally the same as with tubular fluorescent lamps.

Ambient-Temperature Sensitivity

With each different lamp shape, the location of the coldest spot is also different, and this has consequences for the mercury pressure and therefore for the ambient-temperature sensitivity. With some shapes, the coldest spot is also influenced by the burning position of the lamp (e.g., base up or base down). The folded, integrated versions often use amalgam instead of pure mercury to stabilize the mercury pressure and thus to minimize the temperature sensitivity.

Mains-Voltage Variations

No fundamental differences compared with tubular fluorescent tubes. See previous section “Tubular Fluorescent Lamps.”

Product Range

Compact fluorescent lamps are being produced in many types with different properties. The more important lamp properties for which different versions are made are: gear integration (integrated or nonintegrated), tube diameter (13 mm and 18 mm), shape, tube length (related to lumen package), lamp circuit, color temperature, and color rendering. Table 3 indicates for all these lamp aspects the range of lamp types available.
Tubular and Compact Fluorescent Lamp, Table 3

Lamp properties versus lamp types

Lamp property

Range of lamp types

Gear integration

Integrated (I)/nonintegrated (NI)

Tube diameter

13 mm/18 mm

Shape

Various

Lamp length

80–200 mm (CFL-I)/100–600 mm (CFL-NI)

Lamp circuit

Electromagnetic/HF electronic

Color temperature Tk

Standard range (2,700–6,000 K)

Color rendering Ra

Ra > 90 (900 series)/80 < Ra < 90 (900 series)

Cross-References

References

  1. 1.
    Van Bommel, W.J.M., Rouhana, A.: Lighting Hardware: Lamps, Gear, Luminaires, Controls. Course Book. Philips Lighting, Eindhoven (2012)Google Scholar
  2. 2.
    Coaton, J.R., Marsden, A.M.: Lamps and Lighting, 4th edn. Arnold, London (1997)Google Scholar
  3. 3.
    DiLaura, D.L., Houser, K., Mistrick, R., Steffy, G.: IES Handbook. 10th edn. (2011)Google Scholar

Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.NuenenNetherlands