Analysis: Energy Efficiency of Domestic Lighting - Halogen, CFL, LED and ESL

A review of energy consumed by everyday electrical lighting at home by electronics expert Andrew Porter, from halogen to compact fluorescent lamps to the all new electron-stimulated luminescence lamps.

England, 24 January 2010. For many, the domestic lighting system has been based upon incandescent lighting, where this works on the simple principle of passing an electric current through a tungsten filament contained within an inert gas (Argon) filled sealed glass envelope, so that the heating effect is sufficient for the tungsten to become white hot.

Tungsten is used because it can be driven to a  high enough temperature, about 2482°C, without melting, whilst emitting white light for a reasonable period of time. However, this means that a considerable portion of the incoming electrical energy is converted into heat rather than light, where the average energy transfer efficiency only provides 10 to 17 Lumens per Watt of electrical energy.

This compares, for example, to 60 Lumens per Watt for white Light Emitting Diode light bulb replacements. In addition, the other factor associated with incandescent lighting is that of tungsten being progressively deposited on to the glass encapsulation causing the gradual dulling of the light bulb to more of a yellow tint rather than white. This process is caused by some of the tungsten reaching a temperature sufficiently high that it is driven away from the filament and deposited on to the class producing a thin coating.

Then, as the tungsten filament becomes thinner with age, the inevitable happens, when switching on the light bulb one day, the electrical inrush current is sufficient to rupture the filament, and the incandescent lamp fails. Most people are familiar with this process by flicking a light switch, to then witness a short flash of light, a clicking sound from the incandescent lamp as the tungsten filament breaks, and the notably brighter white light emitted from the incandescent light bulb of the same type used the replacement.

Halogen lamps, in comparison, are slightly better, where these work in a somewhat different manner. Instead of using a glass encapsulation, many use quartz. This helps because the quartz encapsulation can tolerate a higher temperature than glass, therefore, it can be situated closer to the tungsten filament. In addition, rather than argon or nitrogen, as used in conventional incandescent lamps, they contain a gas from the halogen group, this group consisting of, for example, iodine or bromine as commonly used in domestic halogen lamps.

Halogen gases have a useful characteristic through combining with tungsten as it evaporates from the filament, helped by the higher running temperature involved, aided with the close proximity of the quartz encapsulation, so that the tungsten is deposited back on to the filament. This means more light, longer life, and better efficiency when compared to a conventional incandescent lamp.

The following two pictures taken from cover the basic encapsulated halogen lamp, and how this can be further encapsulated to produce a unit that is very similar in appearance to a conventional domestic incandescent lamp.

Many have noticed that white car headlamps used to start fading towards yellow as they age. This was simply as a result of being basic incandescent filament lamps. When car headlamps changed to halogen lamps, the failure rate reduced significantly, and the light quality was much better with a sharp white colour, and no yellowing with age. With reference to Figure 2, many car headlamps are now very similar in appearance to the quartz halogen lamp shown. As to efficiency, some incandescent lamps were as poor as 5%, that is, 95% of the incoming electrical energy was converted to heat, and even the better halogen lamps only about 9% efficient.

At this stage, there is one advantage that needs to be considered before dismissing the incandescent and/or halogen lamps as being all bad, and that is Power Factor. In an ideal situation, all Alternating Current Loads, as is inevitable with a domestic 230Vac or 115Vac electricity supply, would present a pure electrically resistive load. This means that the alternating electrical produced by the Electricity Generating Station, operating at 50Hz or 60Hz, that is 50 cycles per second or 60 cycles per second, each cycle following a complete 360° path in a sine-wave profile, would have the current and voltage following exactly the same profile with respect to time, thereby reducing the power loss due to having the Current and Voltage perfectly in phase. Any load that does not consist of pure electrical resistance, such as an inductive or capacitive load, means that there is a phase shift between voltage and current, so that the electricity generating station has to generate more electrical power to compensate. The following images should help to explain this principle: 

The waveform shown above represents, in this example, a domestic Power Line Voltage or Current profile, where 'A' represents the Voltage or Current Peak Value, and 'T' represents the Time for one complete cycle. If the Current and Voltage are perfectly in phase, then the two waveforms, identical in shape to that shown above, would rise and fall in exactly the same manner at exactly the same point in time. If shown with the same amplitude graphically, they would perfectly overlap. In the case of the Domestic Electricity Supply, this means that the electrical load is a pure electrically resistive load, and does not contain any reactive components, such as Inductance and/or Capacitance. In this example, the Power Factor is given a numeric value of 1, as the Voltage and Current are following identical profiles with respect to any given point in time.

This image shows that the Current and Voltage, whilst sharing exactly the same profile in terms of shape, are now shifted in time. This is known as a Phase Shift, where the unit of Phase Shift is Degrees, as per angular displacement, where one full cycle, represented by T in figure 4 indicates 360°. The symbol ϴ represents the magnitude of phase shift in angular degrees.

Assuming that loss free power transmission takes place between the Electricity Generating Station and  the domestic electrical load, in this case lighting, and we take the load as being 100W, then with a perfect Power Factor of 1, represented by Figure 1, means that 100W would be needed at the Power Generating Station. However, if the domestic electrical load  had a Power Factor of 0.7, a situation caused by our domestic electrical load not being a pure electrically resistive load, a new issue becomes apparent, as follows: 

 Apparent Power VA = Watts divided by PF

V = Voltage in Volts

A = Electrical Current in Amperes

The Watt is the unit representing true Electrical Power

PF = Power Factor

Apparent Power, in our example, is found as follows:

VA = 100


VA = 143

This means that while the domestic item may be rated at 100W in terms of the cost charged by the electricity supplier, the actual amount of power needed at the electricity generating station is 143W, where 43W is now wasted power. As to how this can be considered in energy, the following, simple conversion can be made:

1Watt equals 1 Joule per Second

This means, for example, that a 100W light bulb will convert 100 Joules of electrical energy per second into light and heat energy. In addition, with the previously mentioned Energy Transfer Efficiency, is this case as low as 5%  for a basic incandescent light bulb, 95% of the incoming electrical energy is converted to heat, and 5% to light. This means most of the incoming electrical energy is wasted.

Fluorescent Light Bulb Replacements

In my home country, the United Kingdom of Great Britain, much emphasis has been placed upon removing inefficient incandescent light bulbs, while promoting compact fluorescent incandescent replacements as the solution. However, while they may, at first, appear to be a solution, it should be noted that they operate in a different manner, and have their own disadvantages that have not yet been fully recognised.

The compact fluorescent lamp replacement, shown on the left, operates by increasing the incoming domestic supply voltage by using a transformer and a small amount of electronic components. The output of this is connected to a number of electrodes, where this causes electrons to shoot off the electrodes into the white coloured fluorescent tube. Inside this tube is mercury vapour or gas, so that when the electrons collide with mercury atoms, it causes the mercury electrons to increase their own energy level.

This makes the mercury unstable, so that when the mercury electrons return to their stable level, they emit light in the ultra violent spectrum, therefore, invisible to the human eye. However, this is where the white coloured internal phosphor coating comes into action, as it converts the ultra violet photons into visible white light. It is similar, in some respects, as to how television receivers using cathode ray tubes convert beams of electrons into the visible picture we see on the screen.

The claimed efficiency of fluorescent light bulb replacements is often stated to be five times better than an incandescent light bulb. However, this does not take into consideration the Power Factor problems, as domestic fluorescent light bulb replacements do not have a perfect Power Factor, nor do they have Power Factor Correction. Going back to Power Factor, the following now emerges: 

100W incandescent lamp = 20W Fluorescent lamp (Claimed)

Power Factor for 100W incandescent lamp = 1

Power Factor for 20W Fluorescent lamp can be as low as 0.5. True power now required from the electricity generating station becomes 40W

Fluorescent lamp is now only 2.5 times more efficient.

100W incandescent lamp = 66W Halogen lamp

Fluorescent lamp is now only 1.65 times more efficient

The standard fluorescent incandescent lamp replacements being promoted in the United Kingdom of Great Britain have a number of problems including inadequate Power Factor, they contain the toxic metal mercury as a gas, they do not yet have safe disposal arrangements, they cannot be used with dimmer switches, they take time to become fully illuminated, and they do not like frequent switching on and off. They are, in many respects, a marginal improvement in terms of electrical power consumption, while presenting a significant number of other problems including environmental toxicity.

Light Emitting Diodes, LEDs

The first issue is to remove two common misnomers, there is no such thing as a pure white Light Emitting Diode, and the colour emitted by a Light Emitting Diode is defined by the semiconductor material that the Light Emitting Diode is made from, not the colour of the encapsulating cover. You can have completely transparent, colourless encapsulations, and yet the colour of light emitted can be virtually any colour as defined by the semiconductor contained therein.

Originally, red Light Emitting Diodes were produced, where these gave out a pure red light. These were quickly followed by other semiconductor materials to provide orange, yellow, green and even invisible light such as Infra Red. Blue was missing, therefore, one of the primary colours of light was unavailable, consequently no means, at that stage, to create white light from a Light Emitting Diode.

Eventually, with new semiconductor materials, a blue Light Emitting Diode was produced. With red and green Light Emitting Diodes already available, means that the three primary colours of light were now a reality. Consequently, three Light Emitting Diodes were placed into one package, one of each primary colour of light, Red, Green and Blue, to produce white light. However, this required additional electronic control to correctly blend the three colours, as any deviation would cause colour distortion. In addition, the total light output was insufficient for any application other than small areas of illumination such as a car dashboard.

LED ColourSemiconductor Material

RED Gallium Arsenide

ORANGE Gallium Arsenide Phosphide

YELLOW Aluminium Gallium Indium Phosphide

GREEN Indium Gallium Arsenide

BLUE Zinc Selenide

VIOLET Indium Gallium Nitride

WHITE Blue Diode with yellow Phosphor

Light emitting diode semiconductor materials.

As blue Light Emitting Diodes continued to evolve, they became cheaper, brighter, and more efficient. Consequently, it became possible to coat blue Light Emitting Diodes with a phosphor, so that the blue light hitting the phosphor would cause the phosphor to react by emitting white light. This discovery meant that the single white Light Emitting Diode became a reality, albeit a blue Light Emitting Diode being the true source of light. In addition, by modifying the phosphor material, a cool white colour, with a hint of blue could be created, or a warm white colour with a hint of yellow. If you like, near daylight white, or a warm white associated with incandescent light bulbs.

As to efficiency, it is about twice as efficient as a fluorescent lamp, when comparing the latest Light Emitting Diode filament lamp replacements. They run a lot cooler, instant on, instant off, can be dimmed if required, easy to Power Factor correct, do not contain mercury, work with timers, and have a very long service life. However, while they are rapidly evolving, the performance in terms of total light output when compared to an incandescent light bulb is only covered by expensive Light Emitting Diode replacements. Therefore for these to become a practical reality requires further evolutionary steps in terms of light output per Light Emitting Diode incandescent light bulb replacement, and purchase cost.

Electron-Stimulated Luminescence Lighting

Electron-Stimulated Luminescence Lighting is a more recent introduction to the market as a direct, domestic, incandescent light bulb replacement with notably greater energy transfer efficiency, quality of light, service life, and absence of toxic materials.

It works on the principle of accelerating electrons provided by the incoming electricity supply, so that the electrons are propelled to hit a phosphor coating inside the glass encapsulation. This phosphor causes white light to be emitted in all directions, just as if it was an incandescent light bulb, in fact, the operating mode is similar to that of a television receiver's cathode ray tube.

In terms of advantages, the following applies:

a) No toxic gases or materials.

b) About 66% less energy than an incandescent light bulb for the same light output. (34W against 100W)

c) Pure white light.

d) Instant on, instant off.

e) Can be dimmed as required with existing dimmer switches.

f) Easy to recycle.

g) Not susceptible to heat.

h) Long life.

i) Costs are comparable to existing fluorescent lamps.

j) Very close to the ideal Power Factor of 1.

h) Can be used with movement detectors so that they can be switched on and off automatically for applications such as security lighting and office lighting (preventing lights from being left operating when they are not needed).

To this extent, they are a direct replacement to existing incandescent lamps without any changes being needed. This compares to fluorescent lamps that require additional electronic circuit elements to work with dimmer switches and Light Emitting Diodes that also require additional electronic circuit elements to work with dimmer switches. In fact, fluorescent lamps and Light Emitting Diodes already need electrical and/or electronic components to work regardless of whether there is an additional need for dimmer switch components or not.

This means that for efficiency, the absence of toxic materials, long service life, quality of light, with absolutely no need to make any changes to existing domestic lighting systems, Electron-Stimulated Luminescent Lighting may prove to be the better option. However, in parallel, Organic Light Emitting Diodes (OLED) are also being produced. Although these have yet to reach their peak evolutionary stage, they may also prove to be another contender for domestic lighting applications.


Domestic incandescent light bulbs have been used for many decades, but they are inefficient as the vast bulk of the incoming electrical energy is converted to heat rather than light. They do, however, present a near perfect electrically resistive load, thereby presenting the minimum stress to the electricity generating station. However, the total power, thus energy demand is very high.

Quartz Halogen lamps are better, give out a bright white light, do not present a power factor issue, but they are still not as efficient as desired in terms of still converting most of the incoming electrical energy into heat.

Compact fluorescent lamps, being promoted as a better replacement, have a number of disadvantages that are often missed. These include the use of the toxic metal mercury, therefore, health and disposal risks. They are also slow in reaching full illumination levels, they can flicker, need additional electrical and electronic components to work with dimmer switches, and present a power factor problem that means that they are not as efficient as claimed. In fact, some people do not like the colour distortion caused by domestic fluorescent lighting.

Light Emitting Diodes, LED, are notably more efficient than incandescent and halogen lights, last significantly longer but, to date, they do not provide the same angular spread of light when compared to incandescent lamps, need additional electrical and electronic components to work, and as white Light Emitting Diodes use a Blue Lighting Emitting Diode with a phosphor coating means that there is a tendency for the white light to be biased towards the blue end of the visible spectrum. However, Organic Light Emitting Diodes, OLED, may resolve these limitations.

For a direct, efficient, pure white light replacement, Electron-Stimulated Luminescence direct incandescent light bulb replacements offer an immediate, direct change without any of the disadvantages associated with incandescent lamps, compact fluorescent lamps, or present generation Light Emitting Diodes. Consequently, until Light Emitting Diode technology evolves further, it is likely that Electron-Stimulated Luminescence will form the best solution for domestic lighting.