Induction Lamps
Electrodeless Fluorescent Lamps
1990s - Today
Introduction & Statistics
HEP Lamps
Inventors and Developments
Introduction:
The induction lamp is a promising technology which features good efficiency and long life. The induction lamp was conceived early on by Nobel laureate J.J Thomson. It was not until the 1960s-1970s when patents for a practical induction lamp were filed by both General Electric and Philips (more on inventors at the bottom of this page). Even then it was not until the 1990s that induction lamps began to see use on a wider scale. They still have not reached full market potential yet and there is still work to do to improve the lamp.
All credits and sources are located at the bottom of each lighting page
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| 1. How it Works | 2. Variations & Uses | 3. Inventors & Developments |
Below: General video on the induction lamp:
Induction Lamps create light by using an electromagnetic field to excite mercury particles mixed in an inert gas like argon or krypton. The mercury creates a UV light and a phosphor on the inside of the bulb or tube filters the energy into visible light. This is a type of fluorescent light. Unlike a standard fluorescent light this does not use electrodes in the tube.
The lamp has three parts: frequency generator (ballast), discharge tube and electromagnet (aka: inductor, energy coupling coils or energizing coils).
1. First the ballast creates high frequency current (between 2.51-3 MHz or 250 kHz for closed ferrite toroid(external lamps)).
2. The current is sent through the electromagnet and an electric field is produced. The number of turns (times the wire is wrapped around the iron core) is determined by how each product is designed (so it is not consistent among different lamps).
3. Energy is transferred from the magnet to the mercury in the tube in the same way that a transformer works... induction.
4. The mercury vapor emits UV light which strikes the phosphor and makes light. GE Genura and Philips QL lamps have a conductive coating to contain electromagnetic interference.Note on mercury use: Induction lamps use a mercury amalgam, amalgams consist of mercury chemically combined with other metals. The mercury amalgam is in a chemically stable state and is not harmful in the way that pure mercury vapor is. Mercury amalgams have been used in dental fillings for over 1000 years.
NOTE: The HEP induction lamp works differently, it uses a nobel gas with metal halide salts to create a high intensity light. The HEP also uses a magnetron to create microwave frequencies, it is described later on.
The ballast is made of four parts. First is an EMI filter to reduce harmonics from the supply of alternating current. The next part is a bridge rectifier, this converts AC to DC power. After that is the PFC circuit which boosts the DC voltage to a constant 400 V value and increases the power factor to 0.95+. The final part of the ballast is an inverter which converts the DC power to high frequency AC. For a more advanced discussion of the ballast and control read here.
Left: John Anderson at GE developed the first commercial induction lamp, building upon earlier work by Peter Cooper Hewitt. Mr. Anderson's breakthrough prototype used a frequency of 13.56 MHz with air core coupler.
Photo: The Schenectady MuseumLongest Life:
The induction lamp can potentially have the longest life of any light source if the ballasts are made with quality in mind.
External Induction Lamp: 85,000-100,000 hours
The external induction lamp lasts the longest due to its design which allows waste heat to escape directly into the air from the coil.
Internal Induction Lamp: 60,000-75,000
The internal induction lamp has the coil buried in the glass envelope bulb. The waste heat eventually damages the induction assembly, see below to learn more about the types of induction lamps.LEARN MORE ABOUT THE CONCEPT OF INDUCTION HERE.
There are three kinds of induction lamps: external, internal and HEP
A.) External Induction Lamp - this uses an induction coil mounted outside of the bulb or tube. The metal coil which is covered by a sheath is clearly visible. A soft or rubberized material is used to prevent the metal ring from coming in direct contact with the glass tube.
High frequency energy is sent from the ballast to the electromagnet. This creates a powerful magnetic field, this excites the mercury amalgam in the protruding small tub (see diagram below). It is normal for mercury when it cools from a vapor form to escape to the coolest part of a bulb or tube, this is usually on the ends of a standard fluorescent tube or HID discharge tube. The small tube is designed to consistently capture the mercury after the lamp is turned off. The tube is located close to the inductor so that the powerful magnetic field easily excites the mercury. The mercury vaporizes and spreads throughout the rest of the tube. It continues to be excited since the magnetic field reaches more than 6 inches in the examples below. If the lamp is large enough two inductors are needed to keep the entire tube area excited. Just as in a standard fluorescent lamp, the mercury vapor creates UV and this is converted into visible light via the phosphor.
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There may be more than one mercury amalgam, others are called assistant amalgams and are located close to the induction assembly.
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Above: If there are two coils on the lamp (above) than both coils are wired in parallel, not in series.
Left: Some external induction lamps are small with a single electromagnet. The electrical field follows a loop within the discharge tube, flowing from positive to the negative side of the electromagnet.
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