22-09-2012, 01:33 PM
Magnetic Design for an Electrodeless Discharged Lamp
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ABSTRACT
We proposed an analysis method for plasma in an electrodeless discharged lamp light-emitting by inductively-coupled plasma, and
a design of a power coupler was investigated by focusing on the electric power from the exciting coil to the plasma. We found that the
power of the plasma was increased and of an Al stage was decreased with moving the core upward. This result suggests that the moving
of the core upward is effective to reduce wasted power loss by eddy current and improves the lamp efficiency. In order to verify the
result, we changed the position of the power coupler in the commercial lamp. Resultantly, the luminous flux of the lamp was increased
by approximately 150 lm (lumen), when the power coupler was moved upward by 25 mm compared with the position of a commercial
lamp. Therefore, we can conclude that our proposed method is applicable to the design of the lamp and suitable design is important to
obtain high lamp efficiency.
INTRODUCTION
RECENTLY, an electrodeless discharged lamp, which has
some industrial advantages such as long lifetime and relatively
high lamp efficiency, is used for a light source with relatively
high luminous flux such as a street lamp [1]. In particular,
the electrodeless lamp with an inner coil [2], [3] shows
high lamp efficiency because driven frequency of several hundred
kilohertz is lower than RF band for outer coil type [2]. Although
the lamp with an inner coil is one of hopeful candidates
for new light source, its lamp efficiency is approximately 90
lm/W and relatively low compared with those for conventional
lamps such as high-pressure sodium ones (110 130 lm/W)
and metal halide ones (70 130 lm/W), which prevents it from
for a further spread. In this type of lamp, as the electric power
is transmitted to the plasma through the magnetic coupling, the
state of the plasma is strongly affected by magnetic factors such
as material, position and shape of magnetic core. A suitable
magnetic design that could supply much electric power to the
plasma is important to obtain the high lamp efficiency because
the light emission of the lamp originates from the plasma. Therefore,
development of an analysis method for Inductively-Coupled
Plasma (ICP) in the lamp is effective to design the suitable
lamp shape.
ANALYSIS PROCEDURE
Model Lamp
Fig. 1(a) shows an analysis object, which is a spherical electrodeless
discharge lamp (150 W type) with an inner coil produced
by Panasonic Electric Works, Ltd. The lamp was composed
of a bulb and a power coupler. A phosphor material was
applied inner surface of the bulb. Ar gas and amalgam (Hgmetal
compound) were enclosed in the bulb, and gas pressures
under lighting were 23.2 Pa and 0.93 Pa for Ar and Hg, respectively.
The power coupler was consisted of an Al die-cast, Cu
tube, a ferrite core and exciting coil. The Cu tube and the Al
die-cast were used for cooling of the core and a stage of the
lamp, respectively.
RESULTS AND DISCUSSIONS
Analyzed Results
Dependences of the , and on the top position of
the core were shown in the Fig. 3. Fig. 4 shows schematic representation
of analysis model. The position of 0 mm corresponds
to the position for the commercial lamp. Increase in and decrease
in were observed by moving the core upward. As distance
between the bottom of the core and the top of the Al stage
is increased when the position is moved to upward, an eddy current
in the Al stage is decreased. Fig. 5 shows eddy current per
unit volume in the power coupler. It is found that large eddy
current flow at the top of the Al stage and Cu tube around the
bottom of the core. Therefore, a design of the power coupler for
reduction in the eddy current in the Cu tube and the Al stage
enables us to improve the lamp efficiency
CONCLUSION
In this paper, we developed a simulation method for low
frequency driven ICP in the spherical electrodeless discharged
lamp with an inner coil and investigated the suitable lamp
design to improve in the lamp efficiency. The obtained results
are summarized as follows:
1) Increase in the distance between the bottom of the core and
the top of the Al stage is one of effective design to obtain
the high lamp efficiency because large eddy current flow at
the top of the Al stage.
2) Large eddy current in Cu tube was observed around the
bottom of the core, and we need to reduce the eddy current
in this part especially to improve in the lamp efficiency.
3) Luminous flux of the commercial lamp was increased with
moving the power coupler upward and we confirmed a
good correlation was observed between analyzed power of
plasma and measured luminous flux of the lamp.