How Induction Lamps work

Magnetic Induction Lamps are amongst the most efficient light sources commercially available. They offer energy savings, long lifespans, high scotopic output and high colour rendering index.

How Magnetic Induction lamps work

Introduction:

Incandescent Lamps:

The most common form of electrical lighting we are all familiar with is the incandescent lamp. This consists of an evacuated glass envelope, which generally has two electrodes protruding through the wall of the glass vessel at the bottom, and sealed in place, to bring the electrical current into the interior of the lamp.

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The incandescent lamp works by passing an electrical current through the filament, typically made of tungsten, which then glows white hot emitting light. This is not an efficient process as approximately 95% of the energy supplied to the lamp is emitted as heat. The filament must be contained in an evacuated bulb, or a bulb filled with an inert gas, as any contact with oxygen will cause the heated tungsten filament to evaporate and break the electrical circuit, thus rendering the lamp useless.

Other Lamp Types:

Fluorescent Lamps:

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Electrodeless Lamps:

• Vibration which breaks the filament, especially when it is hot;
• Failure of the seal integrity of the lamp; typically caused by thermal stresses in the area where the electrodes go through the glass walls. The failure of the seal can either be sudden and complete, or a "slow leak" over time allowing the entry of atmospheric gasses which contaminate the interior.

• Depletion of the mercury amalgam inside the envelope [bulb]. When the mercury ions are excited and bombard the phosphors [which then emit the light we see], a small percentage of them are absorbed by the phosphor coating over time. Once the mercury ions inside the envelope are depleted, the lamp emits only a very dim light and has to be replaced.
• Failure of the electronics [ballast] used to drive the lamp. This is not a catastrophic failure mode as typically the electronics [ballast] are external to the lamp and can easily be replaced.

Magnetic Induction Lamps:

Rectangular and Round External Inductor Lamps - Click To See Larger Version

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The external inductor lamps have the advantage that the heat generated by the induction coil assemblies is external to the tube and can be easily dissipated by convention into the air, or conduction into the fixture. The external inductor design lends itself to higher power output lamps which can be rectangular or doughnut shaped. In the internal inductor lamps, the heat generated by the induction coil is emitted inside the lamp body and must cool by conduction to a heat-sink at the lamp base, and by radiation through the glass walls. The internal inductor lamps tend to have a shorter lifespan than the external inductor types due to higher internal operating temperatures. The internal inductor type looks more like a conventional light bulb than the external inductor type lamps which may be more appealing in some applications.
As with conventional fluorescent lamps, varying the composition of the phosphors coated onto the inside of induction lamps, allows for models with different colour temperatures. The most common colour temperatures of induction lamps are 3500K, 4100K, 5000K and 6500K.
Induction lamps require a correctly matched electronic ballast for proper operation. The ballast takes the incoming mains AC voltage [or DC voltage in the case of 12V and 24V ballasts] and rectifies it to DC. Solid state circuitry then converts this DC current to a very high frequency which is between 2.65 and 13.6 MHz depending on lamp design.
This high frequency is fed to the coil wrapped around the ferrite core of the external or internal inductor. The high frequency creates a strong magnet field in the inductor which couples the energy through the glass walls of the lamp and into the mercury atoms inside the tube.
The ballasts contain control circuitry which regulates the frequency and current to the induction coil to insure stable operation of the lamp. In addition, the ballasts have a circuit which produces a large "start pulse" to initially ionize the mercury atoms and thereby start the lamp. The induction lamps do not start at 100% output - they start at between 75% and 80% output. It takes between 60 and 120 seconds for the mercury bearing amalgam in the lamp to heat up and release enough mercury atoms for the lamps to reach 100% light output.
The close regulation of the lamp by the ballast, and the use of microprocessor controlled circuits allows the ballasts to operate at around 98% efficiency. Only around 2% of the energy is wasted in the induction lamp ballast compared to the 10-15% wasted in traditional "core and coil" type designs used with most high output commercial and industrial lighting.

Induction Lamps Vs. LED Lamps:

While induction lamp technology has matured in the last few years, is often overlooked or underutilized in lighting applications since none of the major manufacturers promote induction lamps in any significant way. LED lighting seems to get the most "buzz" in the market as LEDs are promoted as the best alternative to conventional lighting due to their longevity. Induction lamps have a lifespan of 80, 000 to 100, 000 hours (depending on type and model), which is much longer than the typical high-power white LED lamp lifespan which is in the 50, 000 to 55, 000 range.

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The major difference between the technologies (other than lifespan) is in conversion efficiency (energy utilization) and costs.
Most presently available commercial LED lighting fixtures have conversion efficiencies in the 35 to 60 Lumens/Watt (L/W) range.[3] LED elements with a conversion efficiency of 70~75 L/W are available, but still quite expensive. There are reports of LEDs with conversion efficiencies of up to 100 L/W operating in research labs, but they are not yet commercially available.
Induction lamps have a conversion efficiency ranging from 65 L/W in low wattage (8 ~ 20 W internal inductor types) to 90 L/W in the high wattage (250 ~ 400 W external inductor models) range.[3] Ongoing research will see some small improvements in these numbers. When considering commercial/industrial lighting and using a 200 W fixture as an example, the induction lamp version will produce 16, 000 Lumens while an LED version would only produce 11, 000 Lumens (about 31% less light) with the same energy input.
Since the most powerful single element LEDs available at this time are in the 20 ~ 25W range, to make a 200W fixture, an array of LED elements must be used. This adds to the expense of the fixture since the cost of these more powerful LEDs is presently quite high and they require custom heat-sinks for thermal management. Since induction lamps use well established and mature glass moulding and coating technology with electronic ballasts (similar to fluorescent lamp technology), manufacturing costs are lower and yields higher than high power LEDs at this time. Typically an induction lamps fixture will cost 50% to 75% less than a similar output LED based fixture. This cost gap will be erased over time as LED production ramps up since sold-state devices are more amenable to cost reduction through mass manufacturing techniques.
The one area in which LED technology offers a significant advantage over induction lamps is ruggedness. Since the LEDs are solid-state devices, they are more resistant to vibration and impact compared to the induction lamps which are made of glass. LED lamps are therefore more suitable for applications where there is high vibration such as in transportation and industrial machinery applications.

The Advantages of Magnetic Induction Lamps:

• Long lifespan due to the lack of electrodes - between 65, 000 and 100, 000 hours depending on the lamp model;
• Very high energy conversion efficiency of between 62 and 90 Lumens/watt [higher wattage lamps are more energy efficient];
• High power factor due to the low loss in high frequency electronic ballasts which are between 95% and 98% efficient;
• Minimal Lumen depreciation (declining light output with age) compared to other lamp types as filament evaporation and depletion is absent (see graph below);
• "Instant-on" and hot re-strike, unlike most conventional lamps used in commercial/industrial lighting applications (Sodium vapor and Metal Halides);
• Environmentally friendly as induction lamps use less energy, and generally use less mercury per hour of operation that conventional lighting due to their long lifespan. The mercury is in a solid form and can be easily recovered if the lamp is broken, or for recycling at end-of-life (see Environmental Aspects Of Magnetic Induction Lamps[4])

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