Download Induction Lighting System - Operating Principles

INDUCTION LIGHTING SYSTEM – OPERATING PRINCIPLES
Induction lighting is based on technology that is fundamentally different from conventional gas sources or incandescent
lamps. Instead of electrodes used in gas discharge lamps or the glowing filament of incandescent, light generation is by
means of induction – the transmission of energy by way of a magnetic field – combined with a gas discharge.
Electrical Transformer Principle
The principle is the same as that of an electrical transformer (Figure 1.). An alternating current (Ip) in the primary coil induces
a corresponding alternative magnetic field in the core and the surrounding space. This magnetic field in turn induces a
current of the same frequency (Is) in the secondary coil. The higher the frequency of the alternating current, the higher the
overall efficiency of the system, and the more compact the system can be.
Induced Current in the Lamp Bulb
The energy source in the induction lighting system – equivalent to the primary coil of the transformer – is the lamp’s
induction coil, which is powered by the high-frequency electronics in the HF generator. The secondary coil is represented
by the low-pressure gas and metal vapor inside the lamp bulb (Figure 2.). The induced current causes the acceleration of
charged particles in the metal vapor. These particles collide, resulting in excitation and ionization of the metal vapor atoms,
and raising the energy level of the free electrons from these atoms to a higher, unstable state. As these excited electrons fall
back to their stable, lower-energy state, they emit ultraviolet radiation. This falls on the fluorescent coating inside the lamp
bulb, causing light to be emitted.
Ultra-long lifetime
The ultra-long lifetime of the induction lighting system is attributable to two main factors:
• There are no filaments or electrodes as in conventional lamps that are exposed to the effects of heat and high
electrical potential, and as a result are subject to deterioration of performance and finally to failure.
• Because the induced magnetic field can easily pass through the glass wall of the lamp bulb, no throughput wires are
needed as in incandescent or discharge lamps, where the glass/metal junction is another vulnerable failure area.
Low Radiated Energy Levels
The high frequency power supply to the primary coil at 2.65 MHz – well outside normal broadcast and communication radio
bands – ensures highly efficient energy transmission between the induction coil and the gas and metal vapor filling of the
lamp bulb. Radiated energy levels close to an induction lighting system are no higher than from a distant radio transmitter,
while the UV radiated power is no more than that of a standard fluorescent lamp of the same power.
Visible light
Metal vapor
atom
Fig. 1. Induction principle: the
alternating current (Ip) in the primary
coil induces by magnetism a
corresponding current of the same
frequency (Is) in the secondary coil.
In the induction lamp system, this
secondary coil is formed by the metal
vapor filling in the bulb.
Fluorescent
powder
Fig. 2. Discharge principle in the
induction lamp bulb, showing how
the free electrons in the metal vapor
filling are excited by the induced
secondary current, resulting in the
emission of ultraviolet radiation. This
strikes the fluorescent coating,
generating visible light.
System Components
The induction lighting system consists of three main components (Figure 3.), each of which can be replaced separately if
service is required:
•
The lamp bulb or discharge vessel (Figure 4.) is a closed glass bulb containing a low-pressure insert gas filling with a
small amount of mercury vapor. The walls of the vessel are coated on the inside with a fluorescent powder of any of the
modern three-line phosphor types, providing a choice of color temperatures (2700K, 3000K and 4000K). The discharge
vessel is fixed to the power coupler by the lamp cap with a “click system”. These two components normally never need
to be disassembled due to the long lifetime of the system.
•
The power coupler transfers energy from the HF generator to the discharge inside the glass bulb, using an antenna
that comprises the primary induction coil and its ferrite core (Figure 5.). Other parts of the power coupler are a plastic
support for the antenna, a 40 cm coaxial connecting cable carrying the current from the HF generator, and a heat
conduction rod with mounting flange. The mounting flange allows the lamp system to be mechanically attached to the
luminaire, and removes waste heat to a heat sink that forms part of the luminaire. The maximum permissible mounting
flange temperature is one of the determining factors that contribute to the system’s long lifetime.
•
The HF generator (Figure 6.) produces the 2.65 MHz alternating current supply to the antenna. It contains an oscillator
that is tuned to the characteristics of the primary coil in the antenna and the 40 cm coaxial connecting cable. The HF
generator also includes preconditioning and filtering circuits to correct fluctuations in the voltage and frequency of the
main power supply, and to prevent distortion from feeding back into the mains. All the generator electronics are housed
in a metal box that provides screening against radio frequency interference and serves as a heat sink. The maximum
permissible testpoint temperature is the other determining factor that contributes to the system’s long lifetime.
Power Coupler
Discharge bulb
Cavity
Auxiliary
amalgam
HF generator
Main
amalgam
Lamp cap
Fig. 3. Main components of the
induction lamp system, showing the
lamp (discharge vessel), power
coupler and HF generator.
Fig. 4. The discharge vessel of the
induction lighting system, in the form
of a closed glass bulb containing a
low-pressure inert gas filling with a
small amount of mercury vapor.
Ferrite core
(inside)
Coll
Coaxial
cable
}
Primary
coil
Antenna
Heating
conducting
rod
Mounting
flange
40 cm Coaxial
cable
Mains
supply
Oscillator
(2.65 MHz)
Preconditioner
+
filtering
HF generator
Fig. 5. The power coupler has the
task of transferring energy from the
HF generator to the discharge inside
the glass bulb.
Fig. 6. The external HF generator
produces the 2.65 MHz alternating
current supply to the primary coil of
the power coupler.
Lithonia Lighting
Acuity Lighting Group, Inc.
Industrial Lighting
One Lithonia Way, Conyers, GA 30012
Phone: 770-922-9000 Fax: 770-918-1209
www.lithonia.com