Note: Descriptions are shown in the official language in which they were submitted.
CA 02433711 2003-06-26
Solid-State Warning Light rwith Environmental Control
The present invention relates generally to warning lights, and more
specifically,
to solid-state (LED) warning lights whose operation is modulated in response
to
environmental conditions, generally under the supervision of a microprocessor
or
dedicated control circuit.
Background of the Invention
Warning lights are useful and desirable on many types of vehicles, machinery,
and other objects (buildings, towers, people, animals, etc.) to announce the
presence,
location, operation mode, status, or function of the vehicle, machine, process
or event.
The nature of warning lights requires them to be employed in harsh physical
environments, often in remote or difficult-access locations, and with limited
availability of
electrical power.
Solid-state fight emitting diodes (LEDs) are well-suited for use in warning
fights
due to characteristics such as good electrical efficiency, small size and
weight, and
rugged construction compared to other light sources such as incandescent
bulbs.
However, existing LED warning lights suffer from a number of problems,
including the
following: circuit complexity (resulting in high production cost and poor
reliability), low
electrical-to-luminous power conversion efficiency (resulting in unwanted
higher
operating temperatures and unwanted higher electrical power consumption), and
limited
ability to operate from a range of electrical supply voltages.
In particular:
~ LED constant voltage circuits require the use of series resistors, causing
unwanted
loss of electrical power as heat;
~ LED constant current circuits require the use of additional circuitry to
measure and
control electrical power exciting the LED; and
~ unregulated circuits require heat producing series resistors and are limited
to
operation over a narrow range of electrical supply voltages, therefore
limiting their
application.
One strategy for controlling LEDs and LED assemblies is to minimize the output
power of the LEDs with respect to ambient lighting levels. In other words,
some LED
driver systems try to provide only enough power to ensure: that the LEDs are
visible
against the backdrop of the ambient lighting. While such an approach might
minimize
power consumption, it does nothing to improve on the actual efficiency of the
conversion
CA 02433711 2003-06-26
from power to fight. More important, by reducing the contrast between the
warning light
and the ambient lighting, the possibility of warnings being missed, increases.
In many
applications this is a tradeoff that is simply not acceptable.
There is therefore a need for an improved LED warninc,~ light.
Summary of the Invention
It is therefore an object of the invention to provide a novel warning light
which
offers some operational advantage over the prior art.
One aspect of the invention is defined as a warning light comprising: an
assembly of light emitting diodes (LEDs); a control circuit operable to drive
the LEDs;
one or more environmental sensors coupled to the control circuit; the control
circuit
further including: means for receiving data andlor measurements from the
environmental
sensors; means for calculating optimal operating parameters for the LEDs,
based on the
environmental data andlor measurements; and means for driving the LEDs in
accordance with said calculated optimal operating parameters.
Another aspect of the invention is defined as a warving light comprising: a
plurality of separate LED sub-assemblies on rigid printed circuits, attached
to a base
circuit board that provides both mechanical and electrical connection between
the rigid
circuit boards and the base circuit board, the separate LED sub-assemblies
being
pointed in different directions; a control circuit operable to drive said
separate LED sub-
assemblies; one or more environmental sensors coupled t:o said control
circuit; the
control circuit further including: means for receiving data a.nd/or
measurements from the
environmental sensors; means for calculating optimal operating parameters for
the
separate LED sub-assemblies, based on the environmental data and/or
measurements;
and means for driving the separate LED sub-assemblies iin accordance with the
calculated optimal operating parameters; allowing the assembly of a multi-
directional
warning light module without the need for costly flexible or bendable circuit
board
materials.
A further aspect of the invention is defined as a warning light comprising: an
assembly of light emitting diodes (LEDs); a control circuit operable to drive
the LEDs;
one or more environmental sensors coupled to the control circuit; the control
circuit
further including: circuitry for receiving data andlor measurements from the
environmental sensors; circuitry for calculating optimal operating parameters
for the
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CA 02433711 2003-06-26
LEDs, based on the environmental data and/or measurements; and circuitry for
driving
the LEDs in accordance with the calculated optimal operating parameters.
Brief Description of the Drawings
These and other features of the invention will become more apparent from the
following description in which reference is made to the appended drawings in
which:
Figure 1 presents a schematic diagram of circuit in a broad embodiment of the
invention;
Figure 2 presents a schematic diagram of an integrated LIED module (/LM)
including an
LED Buck Boost Channel (LBBC) in an embodiment of the invention;
Figure 3 presents a schematic diagram of an integrated LED module (/LM)
including an
LED Buck Down Channel (LBDC) in an embodiment of the invention;
Figure 4 presents a schematic diagram of a warning light circuit in a CM-LM
(Control
Module - LED Module) configuration, including an LBBC circuit in an
embodiment of the invention;
Figure 5 presents a schematic diagram of a warning light circuit in a CM-LM
configuration, including an LBDC circuit in an embodiment of the invention;
Figure 6 presents an exemplary physical layout of a planar ILM including an
LBBC
circuit in an embodiment of the invention;
Figure 7 presents an exemplary physical layout of a planar ILM including an
LBDC
circuit in an embodiment of the invention;
Figures 8 and 9 present top and front views, respectively, of a cylindrical
warning light
using an ILM including an LBBC circuit, in an embodiment of the invention;
Figures 10 and 11 present top and front views, respectively, of a planar
warning light
including light-control-film, in an embodiment of the invention;
Figures 12 and 13 present top and front views, respectively, of a warning
light having a
square cross-section, and including light-control-film, in an embodiment of
the
invention;
Figures 14. and 15 present top and front views, respectively, of a warning
light having a
rectangular cross-section, employing multiple ILMs, and including light-
control-
film, in an embodiment of the invention;
Figures 16, 17 and 18 present front, top and isometric views, respectively, of
a
cylindrical warning light employing multiple side-emitting LEDs, in an
embodiment of the invention;
CA 02433711 2003-06-26
y
Figures 19, 20 and 21 present front, top and back views, respectively, of a
warning light
employing multiple LEDs with optical lenses, in an embodiment of the
invention;
and
Figures 22 and 23 present front and rear isometric views, respectively, of a
warning light
employing multiple LEDs with optical lenses, in an embodiment of the
invention.
Description of the Invention
An electrical schematic diagram of a warning light which addresses one or more
of the objects outlined above, is presented in Figure 1. This warning light
includes an
assembly of light emitting diodes (LEDs) 10, a control circuit 12 operable to
drive the
LEDs 10 and one or more environmental sensors 14 which are electrically
coronected to
the control circuit 12. Specific examples will be described in greater detail
hereinafter,
but may include, for example, devices to sense the following environmental
conditions:
~ ambient temperature;
~ internal temperature;
~ ambient light level;
~ emitted light level;
~ relative humidity;
~ liquid moisture;
~ mechanical tilt;
~ vibration;
~ physical shock;
~ marine wave height and period;
~ air pressure;
~ barometric pressure;
~ solar cell voltage;
~ battery voltage;
~ supply voltage.
Typically, these sensors will be mounted on a circuit board within the warning
light, but
may also be mounted externally or on an outside surface of the warning light.
A number of environmental sensors and their application strategies are
described
hereinafter, but two that are particularly useful are the monitoring of supply
voltage and
ambient temperature. The control circuit 12 can adjust to the available power
level of
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CA 02433711 2003-06-26
the supply voltage, varying the frequency andlor duty cycle of pulses to the
LEDs 10
(duty cycle referring to the percentage of the time that the LEDs are
illuminated in
proportion to the time they are dark). For example:
if the available voltage level is too high, the frequency of pulses to the
LEDs 10
can be reduced. Using the inductive driver circuit described hereinafter, the
LEDs 10 will not be over-driven; or
if the available voltage level is too low, the number of LEDs 10 being driven
can
be reduced, or the duty cycle of the pulses to the LEDs 10 can be decreased to
conserve power.
The power level that LEDs 10 can withstand has to be de-rated with high
ambient
temperatures. Using an ambient temperature sensor, LEDs 10 can be driven at
their
optimal levels without fear of damage.
The control circuit 12 also includes the following components:
1. circuitry for receiving data and/or measurements 16 from the environmental
sensors 14;
2. circuitry for calculating optimal operating parameters 18 for the LEDs 10,
based
on the environmental data andlor measurements; and
3. circuitry for driving 20 the LEDs 10 in accordance with the calculated
optimal
operating parameters.
The actual hardware and/or firmware that is used to implement the circuitry
for
receiving data andlor measurements 16 will depend on the general design
strategy and
upon the nature of the environmental sensors 14 themselves. In some cases, the
environmental sensors 14 may consist simply of switches which are actuated
when a
certain condition arises, which can be handled by the control circuit 12 using
a simple
digital input. In other cases, analogue signals may be provided by the
environmental
sensors 14 which require some conditioning or filtering, an analogue input on
the control
circuit 12 or external conversion from analogue to digital signals. These
design issues
would be clear to one skilled in the art from the teachings herein.
Clearly, the control circuit 12 itself could be implemented using a dedicated
circuit, ASIC (application specific integrated circuit), microcontroller,
microprocessor or
the like, and any necessary supporting components. This design choice will
generally
determine how the circuitry for calculating optimal operating parameters 18
and the
circuitry for driving 20 the LEDs 10 wiN be effected. The circuitry for
calculating optimal
operating parameters 18, for example, could be effected in a microprocessor in
the
s
CA 02433711 2003-06-26
manner of actual calculations which are performed. Alternatively, it could be
implemented by indexing a stored lookup table.
Microprocessors and microcontrollers are the most logical choices because of
their great processing power and programming flexibility. Different models of
LEDs will
have different performance parameters. Having a programmable controller makes
the
task of accommodating a new LED model much easier.
The circuitry for driving 20 the LEDs 10 will be determined by the number and
size of the LEDs 10 (which determines the power required), the manner in which
the
LEDs 10 are wired, and the patterns that are desired. LEDs 10 are commonly
wired in
series, parallel, a combination of the two, or individually. l'he invention is
not limited by
the manner in which the LEDs 10 are wired. Clearly, wiring the LEDs 10
individually
provides the greatest flexibility in the generation of different patterns.
Ganging LEDs 10
together however, results in much less complexity and less wiring
This circuit provides a solid state warning light with many advantages over
the
prior art. Most importantly, it optimizes the light output in view of
environmental
conditions. This is quite distinct from prior art warning lights described in
the
Background, which typically endeavour to minimize the power consumed, and
hence,
minimize the output light level with respect to certain conditions. The prior
art does not
teach that the light level should be optimized, but on the contrary, that it
should be
minimized - the prior art attempts to set the lighting level at the minimal
acceptable level
with respect to the ambient light level.
A number of various embodiments of the invention will now be described. These
embodiments address a number of the other problems found in the art.
Figure 2 presents an electrical schematic diagram of a warning light in which
LEDs are excited by an inductive switch-mode boost circuit controlled by a
microprocessor. This circuit may be operated from supply voltages where the
sum of
the LED junction voltage drops is greater than the supply voltage.
All components and circuitry may be constructed on a single printed-wiring
circuit
board which is referred to herein as an Integrated LED Madule (ILM). The LEDs
D1 to
DN are driven by an LED Buck Boost Channel (LBBC). Transistor (~1 should be a
transistor with the characteristic of low on-state resistance (much less than
one ohm).
L1 should be an inductor with low resistance and high inductance value
(highest Q factor
practical). D1 to DN should be a series branch of LEDs of high output luminous
flux and
CA 02433711 2003-06-26
capable of high current operation. The number of LEDs should be chosen so as
to have
a cumulative forward junction voltage drop higher than the supply voltage.
U3 microprocessor (or microcontroller) should be of low power consumption and
with suitable output pin drive capability to reliably assert the control pin
of transistor Q1
alternately from off-state to on-state. U1 represents an over-current
protection device
and may be a suitably rated positive-temperature-coefficient fuse. U2
represents a low-
power voltage regulator to provide a suitable current supply for the
microprocessor U3.
U4 represents an Analog-to-digital convertor used to detect and measure the
electrical supply voltage. This information is used by the rnicroprocessor to
adjust th
pulse duration and pulse repetition rate used to excite the LEDs D1 to DN. The
microprocessor U3 may use software look-up tables or an algorithm to determine
the
optimum pulse timing to apply to the LED excitation circuit. The
microprocessor U3
alternately switches the transistor Q1 from off-state to full conduction on-
state at a rate
of approximately 100 KHz (design frequency can be chosen over a broad range to
match the choice of inductors and LEDs).
The high pulse rate (approximately 100KHz) of the LED excitation circuit
results
in a visual effect of apparent constant illumination. An observer has no
impression of
pulsation of the LEDs emitted light.
During the transistor t~1 on-state, current flow increases through the
inductor L1
to the common node, developing an electromagnetic field in the inductor L1.
IVo
conduction occurs through the LEDs D1-to-DN at this time:. During the
transistor Q1 off-
state current flows through the inductor L1 and LEDs D1 to DN causing light to
be
emitted. A repetition rate should be chosen so as to allow the electromagnetic
field in L1
to completely collapse and ali current flow through the LEDs to cease before
starting a
new (~1 on-state.
A discrete rectification diode is not employed in thi;~ circuit as this
function is
performed by the LED junction(s). An output filter capacii:or is not employed
either as
there is no requirement for voltage ripple smoothing. Hence, the entire
excitation circuit
is implemented without any resistors, capacitors or rectifying diodes.
LEDs are a very efficient and durable light source. ~ther light sources used
in
the art such as incandescent or halogen bulbs, and xenon flash tubes are less
durable
and less power efficient.
LEDs however, require a controlled electrical power source for operation. The
inductive excitation circuit of the invention is very efficient,
straightforward in design and
CA 02433711 2003-06-26
inexpensive. This is in contrast to the typical LED driving circuits used in
the art which
suffer from problems such as:
~ additional circuit complexity, resulting in unwanted higher production cost
and poorer
reliability;
~ lower electrical-to-luminous power conversion efficiency, resulting in
unwanted
higher operating temperatures and unwanted higher electrical power
consumption;
and
~ limited ability to operate from a range of electrical supply voltages.
In particular, the LED driving circuits used in the art are generally one of
the
following designs:
1. LED constant voltage circuits, which require the use of series resistors.
This
design has the poorest efficiency as most of the electrical energy is wasted
as
heat;
2. LED constant current circuits which require the use of additional circuitry
to
measure and control electrical power exciting the LED. Typically, current
regulated LED circuits employ series current-sense resistor and sensitive
analog-
to-digital conversion circuits; expensive and complex to build, and having a
high
parts count; and
3. unregulated circuits require heat producing series resistors and are
limited to
operation over a narrow range of electrical supply voltages, therefore
limiting
their application.
In contrast, the inductive excitation circuit of the invention is inexpensive,
has a
low parts count, does not use heat producing resistors, and can be monitored
and
controlled by the microprocessor. The pulsed direct-current nature of the
inductive
excitation circuit also enables operation from a wide range of electrical
supply voltages;
therefore, it can be operated from a wide range of electrical supplies
including regular
and rechargeable batteries, solar panels and automotive electrical systems.
Using a microprocessor U3 at the heart of this circuit provides for great
flexibility.
The microprocessor can perform measurements on various environmental factors
affecting the warning light (such as electrical supply voltage, ambient
temperature, etc.)
and automatically adjust its operation according to need. These environmental
sensors
30 are generally mounted on the same circuit board as the microprocessor U3
but can
also be installed on the housing of the ILM. The microprocessor U3 can also
provide
additional functionality including the following:
CA 02433711 2003-06-26
1. the microprocessor U3 may excite the LEDs ~1 to ~N in bursts so as to
produce
obvious pulses of light. The bursts may be of very short duration so as to
give
the appearance of a "strobe-light°', or in longer duration bursts to
produce a
blinking or flashing effect;
2. the microprocessor U3 could also send and receive information from a remote
control or through a communications channel, making the warning light part of
a
network. The ability to communicate over a network allows the new warning
light
to respond in useful ways to instructions from a remote source or to
automatically
adjust its own operation to changes in its operating environment in co-
operation
with other devices on the network. As part of a network the warning light can
receive commands via a data-communications network (using interface COM1 )
to alter its operation, for example, receiving commands toy
a. start or stop operation in response to certain events;
b. changing its operation from a strobing effect to a flashing effect;
c. reducing output power in a controlled way during periods of scarcity of the
electrical power supply (low batteries, lack of light for solar cells or grid
brown-out, for example); or
d. increasing power output in a controlled way during times of increased
need such as impaired atmospheric visibility.
The communications port could also be used to transmit data from the various
environmental sensors or advise on the status of the warning light itself.
Communications between the warning light and a remote control or network may
be implemented by a single or multi-wire interface or over a wireless link
such as
infrared (1R) or radio frequency (RF) link. Many such computer, communication
and instrumentation networks are known in the art;
3. the microprocessor U3 may include an on-board, time-of day clock and
calendar
allowing the warning light to modify operation in response to diurnal and
seasonal requirements; or
4. additional banks of LEDs 32 could be driven by the microprocessor U3, with
different control signals being sent to different banks of LEDs. This could be
used to generate different patterns or displays such as direction arrows or
chasers. Different colours could also be used for the different banks of LEDs.
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CA 02433711 2003-06-26
Figure 3 presents an electrical schematic of a circuit that is similar to that
of
Figure 2, except that it employs an LED Buck Down Channel (LBDC) rather than a
LED
Buck Boost Channel (LBBC). This circuit is useful where the sum of the LED
junction
voltage drops may be less than the supply voltage. This circuit is that same
as Figure 2
except that the LBDC circuit feeds the LEDs D1 to DN in series with a
transistor Q2 and
an inductor L2, and employs a voltage level shifting device U5 to bias the
transistor Q2.
It also includes a "freewheel" diode DF, which carries the reverse recovery
current for
the LBDC. Othervuise, the circuit is the same as that of Figure 2.
Figure 4 is the same as Figure 2, except that rather than providing all of the
components of the circuit on a single board, in the form of an ILM, this
Figure presents
the division of components where separate LED Modules (LM) 40, and ControV
Modules
(CM) 42 are used. Similarly, Figure 5 presents the division of components that
would
be used for the circuit of Figure 3, again, where the LED module (LM) 50 is
separate
from the module containing the microprocessor U3 and excitation circuitry,
control
module (CM) 52.
Figure 6 presents an exemplary physical layout of a planar warning light
module
using the LBBC circuit of Figure 2. In this case only two LBBC circuits are
presented:
LBBC1 and LBBCn, but many more could also be used. As shown, the LEDs are
preferably arranged adjacent their respective inductors L1, Ln and transistors
Q1, Qn.
The balance of the electronic components are preferably installed in
accessible locations
which do not interfere with the physical positioning of the LEDs or the
potentially hot
excitation components.
Figure 7 similarly presents an exemplary physical layout of a planar warning
light
module using the LBDC circuit of Figure 3. In this case only two LBDC circuits
are
presented: LBDC1 and LBDCn, but many more could also be used. As shown, the
LEDs are preferably arranged adjacent their respective inductors L2, Ln and
transistors
Q2, Qn. The balance of the electronic components are preferably installed in
accessible
locations which do not interfere with the physical placement of the LEDs or
the
potentially hot excitation components.
Figures 8 and 9 present top and front views respectively, of a physical layout
of
a cylindrical warning light in an embodiment of the invention. A rugged,
lightweight
housing of extruded aluminum alloy with an anodized surface and a clear,
colourless
polycarbonate lens would be used to protect the Integrated LED Module (ILM) 60
shown
i0
CA 02433711 2003-06-26
in these two figures. Silicone gaskets provide weather-resistant joints
between housing
and lens, and around the cable entry.
The ILM assembly presented in Figures 8 and 9 may be constructed with
conventional low-cost Printed Wiring Circuit Assembly techniques. The cylinder
is
formed by attaching multiple, rigid, LED sub-assemblies 62 to a rigid base
circuit board
64 by means of multi-pin right-angle pin headers 66 that provide both
mechanical and
electrical connection between the circuit boards. This construction technique
allows the
assembly of an omni-directional warning light module without the need for
costly flexible
or bendable circuit board materials.
A warning light of this configuration can be used to emulate a rotating
warning
light without any moving parts. This is done simply by illuminating successive
columns
of LEDs or groups of columns, in a pattern which cycles around the warning
light. Being
entirely solid state, this warning light is physically lighter, more durable
and less
expensive than comparable mechanical warning lights.
Figures 10 and 11 present top and front views respectively, of a physical
layout
of a planar warning light in an embodiment of the invention. Like the warning
light of
Figures 8 and 9, this warning light would typically be encased in a rugged,
lightweight
housing 70 of extruded aluminum alloy with an anodized surface and a clear,
colourless
polycarbonate lens 72 would be used to protect the Integrated LED Module (ILM)
74
shown in these two figures. Silicone gaskets provide weather-resistant joints
between
housing and lens and cable entry. Selectively applied Light Control Film (LCF)
76
refracts light emitted by the LEDs to modify the viewing angle. A multi-
conductor cable
(not shown) may provide electrical power and connections to a data-
communications
network.
Most light sources (including LEDs) require a means to control the direction
and
intensity of the emitted light. Lenses and reflectors can be expensive to
manufacture
and have size and shape characteristics that limit their application. Glass
lenses, for
example, are bulky, heavy, expensive and fragile. Plastic lenses are also
bulky and
have poorer light transmission characteristics. As well, injection-moulds for
plastic lens
have high initial cost. Reflectors tend to be large and bulky and their
geometry favours
the use of single point-source light types.
Light Control Film (LCF) 76 may be used to reflect and refract light from the
LEDs into useful patterns. LCF is a thin transparent film that contains
microscopic
features (micro-louvers, dots or squares, for example) that control the
direction of visible
11
CA 02433711 2003-06-26
light passing through it. Light entering the film from one side can be emitted
from the
other side with its path altered by a significant angle, for example, being
refracted by an
angle of 30 degrees. The film may be constructed of polycarbonate and is
available
from 3M corp. LCF is thin, rugged and flexible, and can be easily worked to
produce a
wide variety of light control effects.
LEDs may also be selected which contain optical lenses integral with the body
of
the LED package and so may not require the use of additicmal lenses or
reflectors to
focus the emitted light.
An array of planar warning lights may be assembled into a single housing for
use
on the roof of a service vehicle to replace the functionality of a
°°light bar'°. The network
capability of the array simplifies the installation and maintenance by
eliminating the large
and heavy bundle of cables traditionally used to control a '°light-
bar'°.
Figures 12 and 13 present top and front views respectively of a rectangular
embodiment consisting of four ILMs 74 in a common housing. Housing 80 may be
substantially square, rectangular, cylindrical or any suitable shape. Light
emitted by the
LEDs is generally perpendicular to flat planes, but is refracfed through 360
degrees by
the LCF 76 to form an omnidirectional beacon. A rechargeable electrical
storage battery
82 located in the center of the assembly can provide electrical power for the
ILMs 74. A
Solar Panel 84 mounted onto or forming the top of the housing may provide
electrical
power for the ILMs 74 or to recharge the battery 82. A wireless radio-
frequency or
infrared link (not shown) may provide connection to a data communications
network.
Such an assembly may operate for a years of time without any wired
connections.
Figures 14 and 15 present top and front views respectively of a linear
assembly
of ILMs 74 in a common housing. ILMs 74 may contain LEDs of different colours
and so
be capable of replacing so-called °'light-bars" used to signal vehicle
identity and
operation by means of colour codes (for example, Red and yllhite indicating
Police,
Ambulance, Fire equipment or Blue indicating Snow removal equipment, etc.)
Figures 16, 17 and 18 present side, top and isometric views of a warning light
consisting of an array of omnidirectional side-emitting LEDs 90. Each side-
emitting LED
90 is mounted on its own circuit board 96 which is fixed to a heat sink which
also serves
as a light directing baffle. Successive circuit boards 92 are separated by
means of
standoffs 94.
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CA 02433711 2003-06-26
This design is easily scalable for any number of LEI~s. Different colours of
LEDs
could be used to implement a tower of warning signals. The assembly of Figures
17, 18
and 19 could also be enhanced by means of cylindrical Fresnel lenses or
regular lenses.
Figures 19 through 23 present various views of an LED module consisting of an
array of LEDs with optical lenses. The array is constructed so as to control
the field-of-
view.
As shown in the top view of Figure 20, three or more LED modules 100 can be
mounted on a single heatsink 102, formed to direct the light in the desired
directions.
The facepfate 104 serves an aesthetic purpose, as well as providing physical
protection
and structure to the assembly. The faceplate 104 is mounted on the heatsink by
means
of standoffs 106. Figures 19 and 21 present front and back views respectively,
of the
same design. Figures 22 and 23 present front and back isometric views
respectively, of
the same design.
The new warning light may be used in many of the traditional warning light
applications but with the benefit of reduced electrical power consumption,
lower initial
cost, improved reliability and longer life. Additionally, the new warning
light may find
new applications enabled by its improved functional characteristics.
Reduced power requirements allow longer running time andlor increased light
output in applications such as battery or solar powered marine installations.
Reduced
initial cost and maintenance requirements imprave the economic feasibility of
use of the
new warning light in cost sensitive and access-restricted environments.
While particular embodiments of the present invention have been shown and
described, it is clear that changes and modifications may be made to such
embodiments
without departing from the true scope and spirit of the invention. For
example, one could
use polarizing film or shadow mask mounted in front of LEDs for the purpose of
contrast
enhancement. The contrast ratio of the warning signal to trre adjacent
background has a
significant contribution to the noticeability of a warning light" and the use
of polarizing
film, shadow mask or other techniques known in the art would improve the
contrast.
13
