System and method for broadcasting colored light for emergency signals

A lighting system and method for broadcasting colored lights as emergency warning signals from a light source. A centralized continuous light source is coupled via a fiber optic transmission medium to an external display location such as a lens or the like located on a vehicle. The color and the relative intensity of each color is periodically modulated to alternate between at least two states such that the contrast between these alternating states is perceived by observers to be a flashing source of light with no off-time. The frequency and the duty cycle of the repetition rate of alternating between the states may be further controlled to better draw attention to the light source. In one embodiment, the external display locations include optical converters, each converter having multiple input facets and optically arranged to broadcast light received at its facets at predetermined vertical and horizontal output angles.

CROSS-REFERENCE TO RELATED APPLICATIONS 
The present application is related to the following copending U.S. Patent 
Applications: "System and Method for Broadcasting Colored Light for 
Emergency Signalling," Ser. No. 08/382,647 by Williams et al., "A Compact 
Uniform Beam Spreader for a High Brightness Centralized Lighting System," 
by William J. Cassarly, Timothy J. Mazies, John M. Davenport and Richard 
J. Hansler, Ser. No. 08/382,717, and "Flashing Lighting System Using a 
Discharge Light Source," by Joseph M. Allison, William J. Cassarly, John 
M. Davenport, Richard J. Hansler, Jacek J. Jozwik, Dennis J. Hilburger and 
Jerry L. Williams, Ser. No. 08/382,713, all filed on Feb. 2, 1995. 
1. Field of the Invention 
The present invention relates generally to lighting systems, and more 
particularly to a centralized lighting system for emergency vehicle 
lights. 
2. Background of the Invention 
Presently, emergency vehicles, including ambulances, police vehicles, and 
emergency fire apparatus vehicles, output visible warning signals through 
the use of a beacon or a light bar mounted thereon, or via flashing strobe 
lights built into the body of the vehicle. A beacon ordinarily houses a 
continuous light source radiated by a rotating reflector, while a light 
bar typically contains a number of flashing (strobing) light sources or 
light sources radiated by rotating mirrors. A flashing strobe light built 
into the body of the vehicle is typically covered by a plastic lens or the 
like to increase its visibility and to achieve a specific color. 
To ensure effectiveness, these lighting systems are required to meet 
certain performance specifications, such as those proposed by the 
Ambulance Manufacturers Division of the National Truck Equipment 
Association, AMD Standard 016. Another ambulance specification, General 
Services Administration Specification KKK-A-1822C, requires a minimum 
number of lights disposed at specific display locations on the vehicle and 
arranged to radiate the light in a certain manner. 
With a beacon, a motorized driving mechanism rotates a parabolic reflector 
in order to alternately block and focus the light radiated to a given 
location so that the light appears to observers to be intermittent rather 
than continuous. The driving mechanism includes a relatively large motor, 
making such beacon systems rather inefficient. Beacons are also limited to 
flashing one color based on the color of the transparent housing 
surrounding the bulb and reflector. 
With strobing bulbs, the desired intermittent light patterns are 
accomplished by repeatedly flashing one or more of the bulbs on and off. 
For example, in a light bar some of the lights are color-filtered so that 
observers can better differentiate between these emergency lights and the 
white and red lights of ordinary vehicles, and so that observers can 
distinguish among the different types of emergency vehicles. However, in 
order to display a variety of colors, a number of bulbs must be provided 
at different display locations in the light bar, each bulb radiating 
through its own colored glass or the like. Moreover, in addition to 
emergency lights, other lights may be added to an emergency vehicle. For 
example, an ambulance is typically outfitted with scene lights, and also 
load lights, to continuously illuminate the various areas around the 
vehicle when parked or to facilitate the loading of a person. 
Although functional, light bars, strobe lights and rotating beacons have a 
number of additional drawbacks associated therewith. One drawback common 
to all three types of lights is that the bulbs often fail as a result of 
road-induced failures of the filaments therein due to shock and vibration. 
The high failure rate necessitates the frequent performance of 
time-consuming testing and maintenance procedures. The operating life of 
these conventional filament-based bulbs is typically on the order of 300 
hours. 
Consideration must also be given to the design and adaptation of vehicles 
for the subsequent installation of emergency lights. Significant mounting 
hardware and wiring is required to add light bars or beacons to a vehicle, 
or to build strobe lights into a vehicle, particularly when converting an 
otherwise standard vehicle to an emergency vehicle. Moreover, the mounting 
of either a beacon or a light bar onto the vehicle can result in a 
reduction in the vehicle's aerodynamics. 
Another drawback that results from the mounting of light bars or beacons 
onto emergency vehicles is that the vehicles necessarily become more 
conspicuous, even at times when no emergency is present and the lights are 
not activated. This is undesirable in certain situations. By way of 
example, police officers often desire to have their police cars remain 
inconspicuous, such as when situating themselves to observe potential 
traffic offenders. 
Finally, ambulances need to have a very stable, high-capacity power source 
so that the sensitive medical equipment present therein operates properly. 
However, flashing intermittent lights produce large, uneven power demands 
and can generate unpredictable electronic noise. Accordingly, ambulances 
having conventional flashing lights must be provided with a 
well-regulated, uninterruptible power source and adequate shielding, such 
as by adding electronic filtering and/or a completely separate power 
system. This increases the complexity and cost of the vehicle. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
emergency vehicle lighting system that provides warning lights to meet 
emergency vehicle lighting specifications without employing 
filament-containing bulbs. 
Another object is to provide a lighting system as characterized above that 
enables each display location on the vehicle to broadcast light in one or 
more distinct colors. 
It is a related object to provide such a lighting system that utilizes a 
continuous light source to efficiently provide a contrasting light pattern 
without requiring rotating reflector. 
It is another object to provide a lighting system as characterized above 
that may be incorporated into a vehicle without significantly altering the 
profile of the vehicle, thereby maintaining the vehicle's aerodynamics 
while allowing it to remain inconspicuous when necessary. 
It is another object to simplify the installation and maintenance of an 
emergency lighting system in a vehicle. 
It is also an object to provide a lighting system of the above kind that 
draws power in a substantially constant manner. 
Another object is to provide an emergency lighting system that broadcasts 
multiple types of emergency lighting signals, such as modulated emergency 
signals, scene lighting and load lighting, from a single optical 
converter. 
Briefly, the invention provides an optical converter for broadcasting 
lighting signals from a vehicle including at least a first beam and a 
second beam of continuous light having a distinct spatial separation. The 
converter preferably includes a plurality of input facets for injecting 
light into it via fiber optic light pipes connected to one or more light 
sources.

While the invention is amenable to various modifications and alternative 
constructions, certain illustrated embodiments thereof have been shown in 
the drawings and will be described below in detail. It should be 
understood, however, that there is no intention to limit the invention to 
the specific forms disclosed, but on the contrary, the intention is to 
cover all modifications, alternative constructions, and equivalents 
falling within the spirit and scope of the invention as expressed in the 
appended claims. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawings and referring first to FIGS. 1 and 2, there is 
shown a lighting system generally designated 10 incorporated into a 
vehicle 12 and constructed in accordance with the present invention. In 
one embodiment, the vehicle 12 is an ambulance including a forward portion 
14 and a rear portion 16. 
An ambulance lighting system may comprise a combination of two separate 
lighting systems as best shown in FIGS. 3A and 3B. In such a 
configuration, the first system (FIG. 3A) includes a plurality of 
emergency lights 18.sub.1 -18.sub.14 disposed around both the front 
portion 14 and the rear portion 16 of the vehicle 12. The emergency lights 
18.sub.1 -18.sub.14 are activated to signal observers outside of the 
vehicle of an emergency situation. The second system (FIG. 3B) includes a 
plurality of auxiliary, or scene lights 20.sub.1 -20.sub.4 located on the 
rear portion 16 of the vehicle 12 at the rear, right and left sides 
thereof. The scene lights 20.sub.1 -20.sub.4 are ordinarily used to 
illuminate the side and rear areas around a parked ambulance to facilitate 
the loading of a person. The particular configuration illustrated in FIGS. 
3A and 3B satisfies ambulance lighting design specifications such as 
General Services Administration Specification KKK-A-1822C, which sets 
forth the minimum number of light sources required on an ambulance and 
their locations. 
In accordance with one aspect of the invention and as shown in FIG. 2, the 
light is piped from one or more light sources (e.g., 22.sub.1) centrally 
disposed in an interior location of the emergency vehicle 12 to the 
exterior thereof. Unlike conventional lighting systems, in the preferred 
embodiment the light sources are not ordinarily intended to be directly 
visible from a viewpoint external to the vehicle. Indeed, the light 
sources may be installed at any convenient location in the vehicle 12, 
such as mounted to the vehicle floor behind or underneath the front seats. 
As shown in FIG. 4, each light source, alternatively referred to as a light 
engine 22, preferably comprises a high intensity discharge lamp (HID) 24, 
a ballast circuit 26 for supplying an appropriate amount of power to 
operate the HID 24, and one or more ports 28 for coupling fiber optic 
light pipes (or bundles) 30 thereto. Such light engines 22 may utilize a 
xenon-metal halide lamp operated by a low-voltage ballast circuit in order 
to continuously provide broadband light as described in U.S. Pat. Nos. 
5,047,695 and 5,317,237. These light engines 22 provide light on the order 
of 2,000 to 15,000 lumens of light and have operating lives of 
approximately 3000 to 5000 hours. (A relatively low voltage signal 
provided to the ballast circuit modulates the output power level as 
described in more detail below.) One type of light engine particularly 
suitable for use in the present lighting system 10 is manufactured by 
General Electric Corporation. This type of light is capable of continuous 
operation at sixty watts, with a peak power level in excess of this 
average when combined with operating periods below this average power 
provided that an overall average power level of sixty watts is maintained. 
Thus, as shown in FIG. 2, the emergency vehicle 12 described herein has a 
number of light engines 22.sub.1 -22.sub.5 disposed in the interior 
thereof coupled to the fiber optic light pipes 30. The light pipes 30 in 
turn act as a transmission medium to transmit the continuous broadband 
light from the light engines 22.sub.1 -22.sub.5 towards the exterior of 
the vehicle 12. Small openings are made in the vehicle body to allow the 
light to be broadcast therefrom. As utilized herein, the term "continuous" 
is intended to mean lights that, when activated, are not intermittently 
illuminated and extinguished, and may generally appear to be continuous to 
a human observer, as distinguished from strobing lights which are 
alternately illuminated and extinguished. Thus, continuous lights include 
lights that are constantly ignited, illuminated or arcing as well as those 
that are pulsed at a high enough frequency wherein the individual pulses 
are not individually distinguishable from one another. As used herein, 
continuous lights may also vary in intensity (such as described in the 
related copending U.S. Patent Application entitled "Flashing Lighting 
System Using a Discharge Light Source," by Joseph M. Allison et al., Ser. 
No. 08/382,713, filed Feb. 2, 1995) and still be considered continuous. In 
addition, the term "broadband" is intended to mean light comprising a 
mixture of visible frequencies of light, typically appearing in 
combination as various shades of white. 
The light pipes 30 are preferably acrylic-based and have an elliptical 
cross-section. The elliptical shape provides desirable dispersion 
characteristics and further allows one such pipe to be conveniently 
extended lengthwise atop another. Light pipes of this type are 
commercially available from Lumenyte Corporation, Costa Mesa, Calif. 
To prevent the heat of the light engines 22.sub.1 -22.sub.n from damaging 
the light pipes 30, the light pipes 30 may be coupled to the light engines 
22.sub.1 -22.sub.n through a cylindrically-shaped piece of quartz or other 
such material. In addition, the quartz may be doped to dissipate 
ultraviolet light. For efficiency, the light engines 22.sub.1 -22.sub.n 
contain ellipsoidal mirrors, the lamp at one focus of the ellipsoid and 
the receiving end of the light pipe 30 (or quartz coupling) positioned at 
the other focus. Once the light enters the light pipe 30, the transmission 
of light therethrough to the external display locations takes place in a 
well known manner. 
At each display location, a light converter 32 is inserted through an 
opening in the vehicle 12, and functions as a lens to radiate the light 
exiting the light pipe 30 in a desirable manner, generally outwardly from 
the vehicle 12. For example, one such lens diffracts the light with 
minimal diffusion to increase the illumination angle from an approximately 
thirty degree cone of light to approximately ninety degrees in the 
horizontal plane. In the vertical plane, the converters 32 typically 
diffract the light between approximately twenty and thirty degrees, 
satisfying typical specifications which require minimum candela readings 
at ten degrees vertical. The converters 32 also serve to protect the 
interior of the vehicle 12 from the outside elements, and may be made of 
transparent plastic or glass. Alternatively, the converters 32 may be 
configured as light diffusers in order to scatter the light and increase 
the apparent area of the light source to an external observer. 
As can be appreciated, the lighting system 10 is relatively easy to install 
in a vehicle, since only a small opening needs to be drilled or cut 
through the vehicle body to provide a passageway for one of the converters 
32, or one of the light pipes 30 or light therefrom to pass through. Each 
converter 32 is inserted through its corresponding opening and preferably 
sealed around its periphery (such as with a rubber grommet) to function as 
both a lens and a protective barrier as previously described. Moreover, 
because the effective exposed area of the converters 32 is small in size 
with respect to conventional beacons or light bars, the profile of the 
vehicle 12 remains relatively unchanged. Thus, with the present invention 
the aerodynamic characteristics of a vehicle are substantially maintained, 
particularly when compared with police vehicles or the like having light 
bars or beacons thereon. 
FIGS. 12A-12D illustrate optical converters 32 suitable for use with the 
present invention. Similar such converters are described in more detail in 
the related copending U.S. Patent Application "A Compact Uniform Beam 
Spreader for a High Brightness Centralized Lighting System," by William J. 
Cassarly et al., Ser. No. 08/382,717, filed Feb. 2, 1995. 
FIGS. 12A-12B are a side view and a top view, respectively, of a converter 
32 optically coupled to an elliptical light pipe 30. The curved surfaces 
33 minimize nulls in the output light distribution as described in the 
previously-identified Cassarly et al. Ser. No., 08/382,717. A converter 32 
of this type has been utilized with the present invention in a prototype 
system configured in accordance with FIG. 9, and diffracts the light so as 
to meet ambulance lighting performance specifications, e.g., ninety 
degrees in the horizontal plane, thirty degrees in the vertical plane. 
FIG. 12C is a top view of a converter 32 optically coupled to an elliptical 
light pipe 30, and configured as a planoconvex lens to refract and 
diffract the received light in a manner that is suitable for use with the 
present invention. A Fresnel lens having comparable optical refraction 
and/or diffraction characteristics may similarly be utilized as an optical 
converter 32. 
FIG. 12D is a top view of another type of converter 32 also suitable for 
use with the present invention. This converter 32 is configured for total 
internal reflection to bend the light received from the light pipe 30 
approximately ninety degrees. The tapering of the converter 32 of FIG. 12D 
diverges the light in the desired manner for broadcasting from the vehicle 
12. 
In accordance with one aspect of the invention, at least some of the 
broadband light provided by the light engines 22.sub.1 -22.sub.5 is 
modulated in order to periodically change output states before being 
broadcast from the vehicle 12. Observers perceive the contrast between the 
different states as flashing. Moreover, in order to meet performance 
specifications for emergency vehicles, the light broadcast from the 
vehicle 12 must appear to observers to be flashing at rates characteristic 
of emergency vehicles, generally between 60 and 240 flashes per minute 
(one to four hertz) as standardized by the Society of Automotive Engineers 
(SAE J-845, SAE J-595, SAE J-1318) for emergency warning lights. Of 
course, these standard rates are not absolute, and thus the system 10 may 
be adapted for broadcasting light at other perceptible flash rates, for 
example rates ranging from 0.1 hertz to 10 hertz. The control circuitry 
for controlling the flash rate is described in more detail below. 
One manner of modulating the light involves periodically modifying the 
spectral composition of the light broadcast from the vehicle 12 at 
selected converters 32 so as to provide lighting of the appropriate colors 
for that type of emergency vehicle, e.g., red, amber and white 
(unfiltered) for an ambulance. The color modulation is preferably 
performed by filtering the broadband light exiting selected light pipes 30 
with a variable filter 34 before it reaches its corresponding optical 
converter 32. To this end, in one embodiment a color wheel 36 (FIG. 4, 
FIG. 7) having the desired color filters incorporated therein is disposed 
between the light pipes 30 and the optical converter 32 to serve as the 
variable filter 34. Alternatively it is feasible to immediately filter the 
light at the light engine 22, i.e., before it enters the fiber optic 
transmission path 30. 
Regardless of the location that the filter 34 is inserted, by connecting 
the color wheel 36 to a motorized driving mechanism 38 (FIG. 4) for 
rotation, the light broadcast from the vehicle periodically changes its 
spectral composition at a rate dependent on the rotation of the color 
wheel 36. Of course, one of the sections (e.g., section 37.sub.1) in the 
color wheel 36 can be transparent to all wavelengths of visible light so 
that one of the broadcast states is white light. Alternatively, one of the 
sections (e.g., section 37.sub.3) of the color wheel 36 may be opaque to 
all frequencies of visible light, enabling the emulation of a conventional 
on-off flash pattern. Such an opaque section may also be used to block 
even low levels of light that may be present during a low-power standby 
mode, described in more detail below. Two or more selectively-oriented 
polarized filters may be arranged in series and coordinated to further 
increase the number of display patterns available. 
In one embodiment of the invention, a plurality of color wheels 36 serve as 
the variable filters 34 and the motors 38 driving the color wheels 36 are 
stepper motors. This enables electrical output pulses to determine the 
direction and speed of rotation of each of the color wheels 36, thereby 
determining the settings of the variable filter 34 and consequently the 
colors of the light broadcasted from the vehicle 12, as well as the 
frequency and duty cycle of the flash rate. One suitable stepper motor is 
manufactured by Nippon Pulse Motor Co., Ltd., commercially available from 
Inland Stepper Motors, Sierra Vista, Ariz., Part No. PF42T-48. 
To modulate the spectral composition of the broadcasted light, a system 
controller 40 is provided as shown in FIG. 5. Preferably, the system 
controller 40 includes a processor 42 operatively connected to a memory 
44, and interfaced to the filters 34.sub.1 -34.sub.n through input/output 
(I/O) circuitry 46. A control panel 48 having at least one switch thereon 
is connected to the system controller 40 to allow the vehicle operator to 
select among preset flash patterns stored in the memory 44, depending on 
the type of emergency situation selected by the vehicle's operator. A 
similar system controller for controlling the flash patterns in an 
emergency vehicle is described in U.S. patent application Ser. No. 
07/592,557, assigned to Federal Signal Corporation, University Park, Ill. 
To provide the current necessary for rotating the color wheels 36, the 
processor is connected to the stepper motor 38 through driver 49, which 
may be a UNC 5804 integrated circuit commercially available from Allegro 
Corporation. To position the color wheel, a position sensor 39 is mounted 
onto one of the sections of the color wheel, e.g., section 37.sub.3 (FIG. 
7), to report the angular position to the processor 42. For example, the 
position sensor 39 may comprise a conductive strip or magnet in 
conjunction with a corresponding switch, such that the switch is closed at 
a certain angular position of the wheel. This provides the processor 42 
with closed-loop control over the filter setting via control of the 
stepper motor 38. If an opaque section is present on the color wheel, the 
metal strip is affixed, e.g., glued, to that section since any blocking 
effect caused by the strip is irrelevant at that wheel position. As shown 
in FIG. 6, a buffer 41 such as a 74HC244 (TTL) integrated circuit may be 
used to connect the sensor 39 (and other such sensors) to the processor 
42. 
In one alternate embodiment, one or more of the filters 34 may include a 
dichroic mirror or the like that reflects only specified frequencies while 
passing the other spectral frequencies to modulate the light. In another 
alternate embodiment, the filters 34 may be electronic filters such as 
liquid crystal displays that enable voltage-controlled filtering of select 
wavelengths of light. In yet another embodiment, the filters 34 may 
comprise acousto-optic tunable filters which filter select wavelengths of 
light across the visible spectrum according to the frequency of an 
ultrasonic signal applied thereto. The use of electro-optic or acoustic 
optic filtering enables the system to function with no moving parts. When 
electro-optic filters are used to filter the light, the I/O circuitry 46 
may include a D-A voltage converter to provide a variable voltage to the 
filter to determine the wavelengths filtered. Alternatively, a switching 
network may be included in the I/O circuitry 46 to enable controlled 
selection between two or more particular voltages. The switching network 
may similarly switch frequencies applied to an acousto-optic tunable 
filter thereby enabling selection of the wavelengths to filter. 
Regardless of the filtering means 34 employed, since the available light is 
not strobed between a fully-on and fully-off state, all of the continuous 
light generated by the light engine 22 may be used. This may provide for 
improved recognition of the vehicle 12, while reducing the startling 
flashes that occur with conventional emergency lights. 
Moreover, utilizing continuous light at varying states provides for 
significant flexibility in the lighting patterns broadcast to observers. 
For example, by controlling the amount of time that each color is 
broadcasted, such as by appropriately timing the positioning of the color 
wheel 36, the flashing colors may be utilized to convey additional 
information from the vehicle 12. By way of example, short red, long amber 
flashes may be used to indicate a vehicle moving at a high rate of speed, 
while long red, short amber may be used to indicate a slowed or stopped 
vehicle. 
In addition to varying the spectral composition of the light, other 
characteristics of the broadcasted light may be modulated. In particular, 
the intensity of the light may be periodically varied such as to enhance 
the contrast between the colors. To this end, the intensity of the light 
engine 22 is controlled by an appropriate control circuit as described 
below. 
It can readily be appreciated that, to a certain extent, the operation of 
filtering itself reduces the luminous intensity broadcasted as a function 
of the wavelength being passed. For example, a red filter reduces the 
intensity more than an amber filter, while the unfiltered state does not 
reduce the intensity at all. Thus, when alternating between red and white 
(unfiltered), the contrast may be enhanced by increasing the power driving 
the light engine 22 to increase the intensity of the lamp 24 during the 
white (unfiltered) state, while reducing the power (and intensity) during 
the red (filtered) state. So that the more intense white light does not 
overwhelm the less-intense red light from the perspective of a viewer, the 
"on" time of the red flash may be a longer duration with respect to the 
"on" time of the white flash. In other words, the duty cycle of the red 
may be greater than fifty percent, the white less than fifty percent. 
However, it can be appreciated that this is only one manner of 
coordinating the spectral composition and intensity. 
Indeed, the intensity settings need not be varied in synchronization with 
the filter settings. For example, the intensity may be varied sinusoidally 
at three hertz while the colors are changed in discrete steps at two 
hertz. The lighting system 10 may be arranged such that the color changes 
may lag or lead the intensity change, be in or out of phase, or such that 
one or both of the modulations may vary randomly. Moreover, the colors 
need not change in discrete steps, particularly if electronic filters are 
used. However, as described herein, for simplicity the colors and 
intensities will be modulated, if at all, in synchronization. 
To modulate the intensities, the system controller 40 is interfaced to the 
ballast circuits 26.sub.1 -26.sub.n of the light engines 22.sub.1 
-22.sub.n through I/O circuitry 46. As can be appreciated, the I/O 
circuitry 46 may include commercially available components such as one or 
more digital-to-analog (D-A) voltage converters or switches connected to 
appropriate amplifiers or attenuators as needed for selectively providing 
control signals to the ballast circuits 26.sub.1 -26.sub.n of the light 
engines 22.sub.1 -22.sub.n to control the desired intensity. The I/O 
circuitry 46 may include electronic shielding, filters and/or 
opto-electronic isolators in order to eliminate ground loops, noise, 
crosstalk and the like. 
As shown in FIG. 6, one such ballast circuit 26 includes a DC-to-DC 
converter 50, e.g., a flyback converter, for converting the voltage of a 
power source 52 such as a car battery to the level necessary for operating 
the high intensity discharge lamp 24. The ballast circuit 26 further 
includes a starting circuit 54 to generate high voltage pulses needed for 
igniting the lamp 24. These high-voltage pulses are generated until the 
lamp 24 is ignited, or until they are disabled by a timer circuit 56 
should the lamp fail to ignite after a predetermined period of time. 
Shortly after ignition, the lamp 24 is at a temperature below its regular 
operating temperature, resulting in poor light output efficiency and a low 
operating voltage. A voltage sensor circuit 58 detects this condition, and 
reports it to a control circuit 60, which is further connected to a 
current sensor circuit 59. The control circuit 60, which comprises a 
differential amplifier connected to adjust for the sensed current and 
voltage levels of the lamp 4, boosts the power to the lamp, e.g., by a 
factor of two, at the low voltage condition. As is well-known in these 
types of DC-to-DC converters, the power supplied to the lamp 24 is 
controlled by the frequency of a switching pulse that discharges the 
primary transformer in the DC-to-DC converter 50. The control circuit 60 
is preferably arranged such that the switching frequency is nominally 
centered around thirty kilohertz so as to be above audible frequencies. 
The increase in power generated by the control circuit 60 at the sensed low 
voltage condition increases the light output, and as a further benefit 
reduces the amount of time that it takes for the lamp 24 to reach its 
regular operating temperature. As the lamp temperature increases, the 
voltage across the lamp 24 gradually increases. As the voltage sensor 
circuit 58 detects this, control circuit 60 appropriately decreases the 
power delivered to the lamp 24 until it reaches its nominal operating 
power, for example sixty watts. 
To controllably vary the light intensity, a small voltage is added or 
subtracted to the sensed voltage input to the control circuit 60, causing 
the control circuit 60 to vary the switching frequency and thus the power 
level applied to the lamp 24. To this end, the processor 42 provides one 
or more output signals to an interface circuit 62 that switches an amount 
of voltage to be added to or subtracted from the sensed voltage. For 
example, a first output signal at a high level may close a solid state 
switch or the like in interface circuit 62 to add an appropriate amount of 
voltage, thereby resulting in a decrease in the power level, while a 
second output signal at a high level may be similarly employed to subtract 
an appropriate amount to increase the power. Alternatively, a 
digital-to-analog voltage converter may be incorporated into the interface 
circuit 62 to enable the processor 42 to offset the sensed voltage level, 
and consequently the power level, over a substantial number of values. In 
any event, the control circuit 60 adjusts the switching frequency and 
therefore the power level according to the sensed voltage as offset by 
voltages controlled by the processor 42. Similar ballast circuitry for 
controlling lamp intensity is described in the related copending U.S. 
Patent Application entitled "Flashing Lighting System Using a Discharge 
Light Source," by Joseph M. Allison et al., Ser. No., 08/328,713, filed 
Feb. 2, 1995. 
Another benefit arising from the ability to control the power to lamp 24 is 
that the lamp 24 may be operated in a low power, standby mode. In the 
standby mode, the lamp 24 remains ignited at a low power level, ready for 
near-instantaneous activation to its full power. This is a significant 
advantage in emergency situations where a warm-up time may be dangerous. 
In addition, such "warm" start-ups obviate the drawing of extra power that 
occurs during a cold start-up, a condition which is stressful to the 
ballast circuit 26, the lamp 24, and the power system. 
It can be readily appreciated that the power settings may be varied in 
either discrete steps or in gradual increments. For example, the intensity 
may vary in a manner corresponding to a ramped function, a sinusoidal 
function, or virtually any function. 
Turning to an explanation of an operation of the invention with particular 
reference to FIGS. 8-11, at step 100 (FIG. 11), the system controller 40 
polls the control panel 48 in order to determine when to activate the 
emergency lighting system 10. As previously described, the switch 
typically resides on a control panel 48 or the like accessible to an 
operator of the vehicle 12. When the control panel 48 indicates that no 
emergency is present, the light engines 22.sub.1 -22.sub.5 are ordinarily 
in the standby mode, effectively off, although not actually extinguished 
so as to be able to fully operate without requiring a significant warm-up 
time. 
Once the actuation of a switch indicative of an emergency mode is detected, 
the processor 42 accesses its memory 44 at step 102 to obtain the 
parameters for operating the emergency lights, for example the several 
optical converters 32 which effectively appear to observers to be the 
"lights" 19.sub.1 -19.sub.20 of FIG. 9. It can be readily appreciated that 
the memory 44 is preferably non-volatile so that such settings are not 
lost upon an interruption of power. The switch or switches on the control 
panel 48 may also be used to indicate a particular mode for operating the 
lights 19.sub.1 -19.sub.20. For example, in the present invention the 
lights 19.sub.9 -19.sub.11 may either be operated as flashing lights or 
continuous scene lights depending on whether the vehicle is moving or 
parked. 
FIGS. 10A and 10B represent look-up tables 81-85 in the memory 44 for a 
first operating mode, while FIGS. 10C and 10D represent look-up tables 
91-95 for a second operating mode. For purposes of simplicity, only the 
first operating mode will be described herein, however it can be readily 
appreciated that the second operating mode functions in a similar manner. 
Moreover, the several display locations around the vehicle 12 will be 
referred to herein as lights 19.sub.1 -19.sub.20, although in keeping with 
the invention they are not the sources that originally generate the light. 
When mode one is selected, the processor 42 reads the look-up table 81 for 
light engine 22.sub.1 (FIG. 9) in the memory 44 and obtains a first power 
setting of thirty-five Watts for a first thirty percent of the cycle, a 
second power setting of sixty Watts for the next forty percent of the 
cycle, and a third power setting of eighty-four Watts for the remaining 
thirty percent of the cycle. The wattage values may be reduced at night 
wherein a lesser intensity may be desirable, again by adjusting 
(increasing) the sensed voltage level. 
The colors for the lights 19.sub.1 -19.sub.4 coupled to light engine 
22.sub.1 are similarly obtained via table 81, i.e., red and white for mode 
one. The length of time of the cycle, for example one-half second, may be 
fixed, or alternatively obtained from the memory 44 or by any other 
suitable means. 
Once the intensities, colors and times are obtained, the processor 44 sets 
the filters and lamps to their initial settings at step 104 and starts a 
timer at step 106. These settings are applied to the lights 19.sub.1 
-19.sub.20 until the first time change, in this example thirty percent of 
the cycle, is detected at step 108. 
At this thirty-percent time, the intensity settings and colors are changed 
at step 110 for certain of the lights as specified by the look-up tables. 
Similar color and/or intensity changes are made to the lights 19.sub.1 
-19.sub.20 during steps 112-120. These steps will not be described in 
detail herein, however, the various settings may be determined by 
following the flow chart of FIG. 11 in conjunction with the look-up tables 
in FIGS. 10A-10D. 
Thus, until deactivated, the process loops between steps 104-122. 
Accordingly, in mode one lights 19.sub.1 -19.sub.6, 19.sub.8 -19.sub.9, 
19.sub.11, 19.sub.17 -19.sub.18 and 19.sub.20 will flash from white to red 
at thirty percent of the cycle, and back from red to white at one-hundred 
percent of the cycle. Lights 19.sub.7 and 19.sub.19 will change from amber 
to red and back to amber at the same times. Light 19.sub.10 will change 
between black and amber while light 19.sub.12 will change from black to 
white, again at the same percentages of the cycle. The corresponding power 
levels will also be modulated at thirty, seventy and one-hundred percent 
of the cycle as previously described. 
However, unlike these particular lights, in the selected mode (mode one) 
lights 19.sub.13 -19.sub.16 will not change in color, remaining red, but 
will change in intensity, from thirty-five Watts to eighty-four Watts. As 
specified in look-up table 84 of FIG. 10B, these changes will occur at 
fifty percent and one-hundred percent of the one-half second cycle. 
The lights are cycled in this manner until at step 122 the control panel 48 
switch is determined to be deactivated, at which time the lights 19.sub.1 
-19.sub.20 are ordinarily returned to their stand-by mode. Of course, the 
detection of the deactivation may occur at any time in the process, for 
example by way of a hardware interrupt. Moreover, the control panel 48 may 
alternatively indicate a change in operating mode instead of indicating 
complete deactivation of the lights. 
Although no particular settings or patterns are necessary to the invention, 
the settings described above have been selected to comply with at least 
one standard specification. For example, as shown in FIG. 8, in the AMD 
specification no white lights may appear in ZONE D, between +135 and -135 
degrees, and similarly, no amber lights may appear in ZONE A, between +45 
and -45 degrees. To ensure that the standards are met, the optical 
converters 32 are selected and arranged on the vehicle body so as to not 
broadcast the light outside of these limits, and the look-up tables have 
been appropriately recorded in memory 44 to properly modulate the output 
colors. 
In alternative arrangements, it may be desirable to have the light pipes 30 
arranged so that all of the light on any one side of the vehicle 12 does 
not originate from a common light engine. With such a configuration, at 
least some light will be visible from all directions in the event that one 
of the light engines 22.sub.1 -22.sub.n fails. 
Finally, the present invention allows lights 19.sub.9 -19.sub.11 to serve 
as both flashing lights and scene lights. For emergency lighting, the 
processor 42 modulates the corresponding filters 34 between two or more 
color settings, ordinarily in conjunction with the intensity as previously 
described. For scene lighting, the processor 42 adjusts the filters 34 to 
an unfiltered setting and sets the intensity as desired, generally to the 
normal operating intensity of the lamp 22.sub.3. 
Turning to FIGS. 13-20, another aspect of the invention contemplates a 
single converter 130 optically configured to receive light from among a 
plurality of light beams and to broadcast those beams at predetermined 
horizontal and vertical output angles. To accomplish this, the converter 
130 has more than one input facet coupled to a common output facet. As 
best shown in FIGS. 17(a)-17(c), the output facet D launches a beam in 
response to the injection of light from a light pipe into one of the input 
facets A, B or C. As shown in FIG. 15, each output beam resulting from 
light injected into the converter 130 from one of the input facets A, B or 
C is distinctly oriented with respect to the other beams. 
As a result, seven distinct outputs are possible from the injection of 
light into input facets A, B and C. Specifically, light injected into each 
one of the input facets A, B or C may be individually converted to a 
distinct directed output beam launched from the output facet D, providing 
three of the possible outputs. An additional output signal can be 
generated at the output facet D by the simultaneous injection of light 
into all three of the input facets. Finally, three other distinct outputs 
can be generated by injecting light into the converter at all possible 
combinations of two of the three input facets--i.e., (A and B), (A and C) 
or (B and C). However, as explained more fully hereinafter, in accordance 
with typical emergency vehicle needs, light is ordinarily injected into 
the converter 130 at only one of the input facets A, B or C at any given 
time. 
The converter 130 includes opposing sidewalls 132, 134, which are 
vertically aligned along the z-axis of FIG. 13 and curved in the x-y plane 
(hereinafter called "the reference plane P"). The surface of each input 
facet A, B, and C of the converter 130 is substantially planar, with a 
plane coincident with the surface of the facet being at an angle with 
respect to the horizontal reference plane P. The thickness of the plastic 
from which the converter 130 is formed defines an edge, which includes the 
surface of each of the input facets A, B and C. Thus, the planar surface 
of each input facet A, B and C forms a 90.degree. angle with each of the 
side walls 130, 132. 
Preferably, the converter 130 is formed from a monolithic piece of 
transparent acrylic plastic with the input facets A, B and C formed in 
portions of the edge between the opposing walls 130, 132. Likewise, the 
output facet D is formed from a portion of the edge of the monolithic 
piece. The input facets A, B and C and output facet D are highly polished 
to ensure total internal reflection using well known polishing techniques. 
In manufacturing, the converter may be injection molded using conventional 
injection molding techniques with a highly polished mold to provide the 
desired level of optical integrity (e.g., SPI/SPE 1). 
As best shown in FIGS. 14 and 15, input facets B and C are formed from a 
top portion of the edge of the monolithic piece of acrylic plastic in 
order to generate output beams launched from the output facet D that are 
angled downwardly with respect to the horizontal reference plane P. In 
contrast, the input facet A is formed along a portion of the edge of the 
monolithic piece of acrylic plastic opposite the edge forming the output 
facet D and aligned with the output facet to broadcast an output beam that 
is centered about the reference horizontal plane P. 
The angles of the plane surfaces of the input facets A, B and C (with 
respect to the horizontal reference plane P) are determined by the desired 
angle of the output beam with respect to the same plane. The relationship 
between the angles of an input facet and the output beam it generates with 
respect to the horizontal reference plane P is determined empirically 
using a computer model, more particularly a personal computer executing 
the application program Opticad.TM. for Windows.TM., version 3.2, 
published by Opticad.TM. Corporation, Santa Fe, N. Mex. In this regard, 
applicants have employed well known ray tracing techniques to determine 
the angle of the input facets A, B and C for desired angles of the 
respective output beams. 
Referring to FIG. 22, to inject the light into the converter 130, light 
pipes 136, 138 and 140 are mated to each facet A, B and C. The opposite 
ends of the light pipes 136, 138 and 140 are connected to an appropriate 
source of light such as a light engine or a modulator output, for example 
the light engine 221 or the variable filter 34.sub.1 in FIG. 5. In keeping 
with one aspect of the invention, the light injected into the various 
facets may be the same color or different colors at each facet, modulated 
light or light directly from a source, and originate from a common source 
or from a plurality of sources. By way of example, a first facet may 
receive light directly (i.e., via a fiber optic connection) from a light 
engine, a second facet may receive the wavelengths of light passed by a 
dichroic filter from the same or a different light engine, and a third 
facet may receive the wavelengths of light reflected by that dichroic 
filter. In an ambulance application, input facets B and C would most 
likely receive white light while output facet A might receive colored 
light either continuously or flashed. 
The ends of the light pipes 136, 138 and 140 are mated to the input facets 
A, B and C in a known manner. More specifically, the end of each light 
pipe to be coupled to the converter 130 is polished and cleaned to have a 
flat face that is perpendicular to the longitudinal axis of the pipe. Each 
flat face is mated to its corresponding input facet using an epoxy resin 
such as Norland Type 68 (UV curing adhesive for plastics), Norland 
Products Inc., New Brunswick, N.J. Because the epoxy tends to be brittle, 
a silicon-based compound 150 in FIG. 13 may be useful for surrounding the 
interface between the light pipe and the input facet as a means for 
protecting the coupling from being damaged or fractured. 
Turning to the optical properties of the converter 130, the profile of each 
of the output beams generated by the converter 130 in response to the 
injection of a light into one of the input facets A, B or C is illustrated 
in FIGS. 15 and 16, and in FIGS. 17a, 17b and 17c, respectively. The 
overall length L of the monolithic piece of acrylic plastic comprising the 
converter 130 is selected in part to ensure that the light launched into 
the converter 130 from each of the light pipes 136, 138 and 140 and its 
respective input facet A, B, or C is fully integrated in the converter 130 
to more evenly distribute the light intensity at the output facet D. In 
the illustrated embodiment, the output facet D has a convex profile as 
indicated in FIGS. 17a-17c in order to form a lens that focuses the light 
launched from the output facet D. The lens formed by the convex profile of 
the output facet D has a focal point at approximately the surface of the 
input facet A and coincident with the horizontal reference plane P. 
The output beam launched from the output facet D from light injected into 
the input facet A has a beam divergence in the vertical plane of 
approximately 10.degree. as illustrated in FIGS. 17a. The output beam has 
a central propagation axis C.sub.A that is coincident with the horizontal 
reference plane P. Thus, this light beam propagates substantially 
horizontally, and, in an emergency vehicle application, such as the 
vehicle 12 of FIG. 1, the beam is preferably employed as a flashing light 
intended to provide an alerting function indicative of an emergency 
situation. 
When light is injected into the converter 130 from the light pipe 138 mated 
to input facet B, the lens of the output facet D launches a beam having a 
profile in the vertical plane substantially as illustrated in FIG. 17b. 
This output beam diverges at an angle of approximately 30.degree. as 
indicated in the illustration of FIG. 17b. The central axis C.sub.B of 
propagation for this output beam is directed downwardly from the 
horizontal reference plane P by an angle of approximately 13.degree.. This 
slight downward propagation of the beam allows it to illuminate the 
immediate surroundings of the emergency vehicle when the converter 130 is 
mounted in the vehicle at an appropriate height such as the height in 
position of the converter 20.sub.1 on the vehicle 12 illustrated in FIG. 
1. Light injected at facet B thus provides a selectively operable lighting 
system for illuminating the scene of the emergency, i.e., "scene lights". 
Light injected into the converter 130 from a light pipe 140 mated to the 
input facet C is converted to an output beam at the output facet D that 
propagates downwardly from the horizontal reference plane P at an angle of 
approximately 26.degree. with respect to the propagation axis C.sub.C. As 
can be seen in FIG. 17c, the profile of the beam diverges in the vertical 
plane at an angle approximately 40.degree.. The downward angle of this 
beam's propagation is well suited for use as a light for illuminating the 
ground immediately adjacent the emergency vehicle 12. Thus, this output 
beam is well suited for providing ground illumination around the doors of 
the emergency vehicle 12, for example to provide a selectively operable 
lighting system for loading an injured passenger into an ambulance, i.e., 
"load lights". 
FIG. 18 illustrates the angle of beam divergence in the horizontal 
reference plane P for each of the output beams at the output facet D. As 
shown, each of the output beams has an angle of approximately 110.degree.. 
Because the periphery of the beam is not well defined, the perimeter of 
each beam in the horizontal and vertical axes has been defined as the 
closed contour where the beam is at approximately 10 percent of its 
average maximum intensity. 
FIG. 15 illustrates the far-field light pattern formed by the three beams 
that can be launched by the converter 130. As can be appreciated from FIG. 
15, this far-field pattern forms three distinct beams. In contrast, the 
near-field pattern, which is illustrated in FIG. 16, is characterized by 
an overlap among the three beams. By altering the relative placement of 
the input facets, those skilled in the art of optics will appreciate that 
the near and far-field patterns of the output beams can be adjusted to 
achieve different patterns than those illustrated. Such variations in the 
specific near and far field patterns are contemplated to be within the 
scope of the present invention. 
In the illustrated embodiment, the monolithic piece of acrylic plastic 
forming the converter 130 is curved along the length of its opposing 
sidewalls 132, 134. Although the curve in the monolithic piece of acrylic 
plastic is not necessary for proper performance of the optics functions of 
the converter 130, the curve or bend allows the converter to fit within 
the cavity between the inner and outer walls of the body 16 of the 
emergency vehicle 12. Referring to FIG. 19, the outer wall 146 of the body 
16 of the emergency vehicle 12 includes a slot 148 through which projects 
the output facet D of the converter 130. Although not shown in the 
drawing, a suitable collar may be fitted around the portion of the 
converter that projects beyond the outer wall 146 of the body 16 in order 
to protect it. 
To mount the converter 130 to the vehicle 12, the converter 130 is held in 
place in the slot 148 by a mounting bracket 150 that is secured to one end 
of the converter as best illustrated in FIG. 13 and to the inner surface 
of the inside wall 152 as best seen in FIG. 19. Because the distance 
between the inner and outer walls of the body 16 is less than the focal 
length of the lens formed by the output facet D, the acrylic plastic piece 
of the converter 130 bends about the vertical z-axis (FIG. 13) such that 
the entire length of the converter fits within the cavity formed between 
the inner and outer walls of the body 16. Because the converter 130 
provides emergency, scene and load lighting, it can replace both types of 
converters 18 and 20 in FIGS. 1-3. 
In an alternative embodiment described with reference to FIGS. 20(a)-20(c), 
the convex lens formed on the facet D may instead be a Fresnel lens 154, 
which enables the output facet D to be substantially flush with the outer 
surface of the body 142. The lens 154 is preferably formed as part of the 
injection molding process for making the converter 130. Alternatively, it 
may instead may be separately formed and glued to a flat facet D. As FIGS. 
20(b) and 20(c) indicate, the Fresnel lens 154 on the output facet D is 
characterized by a surface that in cross-section has a serrated profile as 
best seen in FIG. 20(c), which is characteristic of the compound lens 
construction of a Fresnel lens. In FIG. 20(c), the variation in the 
profile of the sensations from triangular to square is exaggerated as will 
be appreciated by those familiar with the construction of Fresnel lenses. 
As can be seen from the foregoing detailed description, there is provided 
an emergency vehicle lighting system and method that provides warning 
lights to meet emergency vehicle lighting specifications without employing 
filament-containing bulbs. Each display location on the vehicle may be 
arranged to broadcast light in one or more distinct colors. The lighting 
system utilizes a continuous light source to efficiently provide a 
contrasting light pattern, and draws power in a substantially constant 
manner. 
Moreover, the lighting system may be incorporated into a vehicle without 
significantly altering the profile of the vehicle. In addition, the 
installation and maintenance of an emergency lighting system in a vehicle 
is simplified. Finally, a single optical converter is provided that 
broadcasts multiple types of emergency lighting signals, such as modulated 
emergency signals, scene lighting and load lighting. 
All of the references cited herein are hereby incorporated in their 
entireties by reference.