2000 Conference Proceedings
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Assistive Communication Systems for Disabled Individuals
using Visible Lighting
Steven B. Leeb
George B. Hovorka,
Elmer .C. Lupton,
Roderick T. Hinman
Massachusetts Institute of Technology
Talking Lights, LLC, Boston, MA
Billie Louise Bentzen,
Randolph D. Easton,
Lisa Lashell
Boston College, Chestnut Hill, MA
Abstract A transceiver system is developed to allows
conventional fluorescent lights to be used as transmitters for
broadcasting audio, textual, graphical, and position information.
Battery-powered, hand-held electronic devices receive the
transmissions from the lights. This technologyique provides high
quality voice transmissions or data transmissions without causing
visible interference visible in the lights.
Introduction
Commercial and public enterprises, museums, schools, medical
facilities and mass transit systems typically provide signs that
list facility organization by floor, possibly with a map or
schematic representation of the store or system. The Americans
with Disabilities Act was enacted to ensure the accessibility of
public facilities to people with disabilities. Accessible
information is an essential aspect of an accessible environment.
. In "Enabling America,'' the authors note that most
"environments can be restrictive in their accessibility for
people with [disabilities]",'' and while many technologies, e.g.,
wireless transmission to hearing aids, captioning, etc., can be
used, "all of these technologies ... can be improved"'' to
maximize cost efficiency, ease of installation and flexibility of
data transmission [1].
We have developed an information transfer system that can
transmit text, graphics, binary computer data, and audio signals.
Theis Talking Lights™ System uses fluorescent lights to
transmit information to a portable, battery powered optical
receiver. The system requires no wiring other than that used for
existing fluorescent lamp fixtures. It can be used anywhere a
fluorescent light can be installed: inside or outside a building;
in a bright sunlight or underground in a subway station; or
inside a vehicle likes a bus or plane. The receiver is designed
with an arbitrarily narrow acceptance angle. That is, the
receiver will "lock on" to the transmission of a light directly
in front of it, ignoring the transmissions of other lights in a
room. A room can be filled with many lights, each broadcasting a
different message. The receiver will decode the messages of each
individual lights as it is panned around the room. The system can
therefore be used for wayfinding or guiding a user through a
facility as. This is illustrated by the drawings in Figure 1,
which shows Talking Lights users receiving textual and audio
information. It also can broadcast the same message on all
lights, providing enhanced aural information to the hard of
hearing.
How Does it Work?
A Talking Lights transceiver set has two parts: a fluorescent
light transmitters and an optical receiver.
Fluorescent Lights as Transmitters:
A fluorescent light is a phosphor-coated tube of glass , with a
wire or electrode at each end, filled with special gases at a
specific pressure. An electric cur-rent passes between the
electrodes, causing the gases to ionize and emit energy. This
energy is absorbed by phosphors on the glass, which emit light
[2]. A "ballast" controls the current, ensuring the lamp starts
or "strikes" and that the current is not too large or too small,
providing desired illumination with maximum lamp life. The
ballast drives the bulb with a rapidly alternating current that
balances the tasks of each electrode as an emitter and collector
of current, again to maximize lamp life.
Figure 1: Talking Lights Text and Audio Receiver Over half of
the artificial light produced in the United States comes from
fluorescent lamps [2]. Fluorescent lighting fixtures are
generally designed to flood an area with light, ensuring good
access for a communication channel. The choice of fluorescent
lamps as data transmitters is appealing in comparison to other
techniques, such as dedicated infra-red or radio transmitters,
because the lamps are already installed in most locations and
provide large broadcast power since they are designed for bright
illumination. Modern electronic lamp ballasts typically alternate
the current in the lamp between 20 and 100 kHz. This alternation
is too rapid to be perceived by the human eye. Hence, the lamp
light appears to be a steady.
In a Talking Lights ARCLight Ô ballast, the frequency of
alternation of current (i.e.the flickering of the lamp light ) is
varied to encode information in the lamp. Current frequency may
be varied smoothly and continuously to encode an audio signal, or
the frequency may move among a limited number of discrete
frequencies for digital data. Several schemes have been proposed
in the past to use fluorescent lights as transmitters [3-6], but
the Talking Lights approach is the first to use modern band-pass
FM for transmit-ting analog and digital information [7]. The
ARCLight ballast has been carefully designed to eliminate
visually perceptible flicker, regardless of data transmitted. It
can even transmit more than one channel of information using a
single lamp, allowing several broadcasts from the same bulb,
analagous to radio stations or TV channels.
Optical Receivers:
An electronic photodetector is used to receive the light from a
fluorescent lamp transmitter. The receiver decodes frequency
variations in the lamp light to recover the transmitted
information. Different circuits are used for recovering text and
audio information. These can be mixed and matched to provide a
"multimedia" receiver. A block diagram of a Talking Lights text
receiver is shown in Figure 2. With appropriate modifications,
similar circuitry can decode audio signals.
A Talking Lights receiver provides the best overall system
performance when used with Talking Lights transmitters. To
support existing installations, a Talking Light receiver could
not be used in principle to also decode the transmissions of
other optical information systems like remote infrared audible
signage systems. Figure 2: Text Receiver Transceiver Set
Together, a fluorescent lamp transmitter and optical receiver
form a complete Talking Lights transceiver set. We are exploring
a number of approaches for configuring the transceiver set. For
example, preprogrammed lights in a building could endlessly
transmit simple numerical location codes or serial numbers. An
intelligent receiver could use these codes to cue the
presentation of visual or audio information stored or programmed
in the receiver. In this scenario, a user might program the
receiver when entering a building, perhaps from a CD-ROM or from
light transmissions in the entryway. Relevant information would
be presented as the user passed different light fixtures.
The lights could also be configured to broadcast custom
information received from a wired input or a power-line carrier
modem. In this case, the receiver would require little in the way
of sophisticated data storage. Instead, it would simply present
information received from the transmitters. This technique was
used in the experimental trials to provide audio directional
guidance to blind users.
Use for Wayfinding by Blind Participants
Eight blind participants were trained to find a mounted Talking
Lights (TL) transmitter. They then traveled two indoor routes
using information provided by TLs and two routes using verbal
route descriptions (VD). All procedures were conducted
individually.
METHOD
Subjects:. Eight persons who had no more vision than light
projection participated in this project. All were active,
independent travelers. Each received an honorarium of $40.00 for
their participation. Participants ranged in age from 32 to 54
with a mean of 44; 5 were male and 3 female; 7 used a long cane
and one used a dog guide; 6 had been blind more than 4 years and
2 less than 4 years; 6 rated their travel capability as
"excellent" and 2 as "good."
Materials: . The evaluation was conducted on the 2nd floor of
the building in which Talking Lights, Inc. is a tenant. It is an
old factory building with multiple and changing uses. The 2nd
floor has irregular wall surfaces, a wide range of door and door
frame styles,, and numerous pipes, ducts and conduits along the
walls. In short, it is unusual, unpredictable building for
persons without vision.
Four routes used for the evaluation; all had the same start.
Nine TLs mounted on moveable wooden supports were used to label
the environment with wayfinding information necessary to travel
the four routes. Routes varied from 44.5’ to 76.2’ in
length, required two to four turns, and required the use of three
to four TL messages. Braille room numbers or labels (women/men)
were provided at a height of 60" for all rooms along the route.
The most complex series of messages was to the rest rooms:
Start
"Room 1one is on the left. Rooms 10 through 20 and the restrooms
are on the right."
At a T shaped intersection:
"Room 12 is on the left. Rooms 14 through 19 and the restrooms
are on the right"
At a T-shaped intersection:
"Room 19 is on the left. Rooms 14 through 17 and the restrooms
are straight ahead"
Between the Women’s/Men’s rest room:
"Women’s room to the left, men’s room to the
right"
The corresponding restroom VD was: "Turn right. Take the next
hall going right. The restrooms are in front of you at the end of
the hall. Women’s room on the left, men’s room on the
right."
PROCEDURE
Participants were familiarized with traveling a route using TL.
They were positioned at home base and told they would be
traveling to Room #14. The practice route was 62.3' long, had
three turns, and used of four TLs. Participants were given verbal
and physical assistance in using the TL system to travel this
route.
Following familiarization with route travel using TL,
participants traveled each of the four experimental routes, using
TL for two and VD for two. Across the entire evaluation, each
route was used four times with each of the two wayfinding
conditions. Order of routes and wayfinding conditions were
counterbalanced across participants. All routes began with
participants in the same position. at the top of the stairs
For each condition the following measures were made:. 1) The
time between the experimenter's stating the destination, and
participant reaching the destination, i.e. touching the room door
or partition. 2) The time between the experimenter's stating the
destination, and until a participant placing a hand on the
Braille sign identifying the destination. 3) N The number of
times a participant "gave up" and asked to be taken back to home
base to start again.
RESULTS
Because participants often took considerable time to locate by
hand the Braille sign once in the vicinity of the destination,
two travel time analyses were conducted: time to reach the
destination and total time including finding the Braille sign to
confirm the correct destination. Mean travel times to reach a
destination are presented in Table 1 for each of the four routes
for both the verbal directions and TL conditions. Corresponding
total time means are presented in Table 2. Note that travel times
are generally consistent with the varying length of each route
(i.e., greater time for longer routes). Because of counter
balancing measures used, a given participant traveled only two of
the routes with verbal directions and two with TL. Thus for
purposes of analysis a one-way repeated measures ANOVA was
conducted to assess the effect of VD vs TL collapsed across the
four routes. Mean times to reach the destination were 90 sec
(se=30 sec) for VD and 117 sec (se=22 sec) for TL , which was not
a statistically significant effect, F(1,7) = p< 1. Mean total
times (including time to find the Braille sign at the
destination) were 149 sec (se=27 sec) for VD and 136 sec (se=28
sec) for TL, again a non significant effect, F(1,7)) = p< 1.
It is important to note that for VD seven trials resulted in
subjects having to restart a trial because of disorientation or
lack of memory for the route’s verbal directions. In
contrast, for TL only one trial required a restart. The
implication of this finding is twofold. First, the travel times
reported above include added time for the re-traveled routes (the
clock was stopped while the participant was guided back to home
base and then restarted once travel began anew). Thus the
analysis of travel times above incorporates the restart measure.
Second, negligible restarts for TL reflect the fact that no
memory for the route is required on the part of the participant;
the light’s messages were constantly available when a
participant was in the vicinity of the light. Thus disorientation
is unlikely.
Table 1: Mean Travel Time (in sec.) to reach destination. Table
2: Mean Total Time (including finding Braille sign,) in sec.)
CONCLUSION
Overall the finding of no difference in travel time for verbal
directions vs.. Talking Lights is quite note-worthy. Verbal
directions are only available to blind people if other people are
present. Additionally, the routes and verbal directions used here
were relatively simple and short. Longer routes and directions
would presumably impose memory loads sufficiently high to result
in travel disorientation and more restarts, a pattern of results
beginning to emerge in the present data as noted above. The
transceiver system using conventional fluorescent lights to
transmit verbal information for wayfinding enabled blind users
who were blind to travel indoor routes with no need for
individual assistance.
Acknowledgements
The authors gratefully acknowledge the valuable advice and
support of Deron K. Jackson whose. His assistance in creating
figures for this paper was essential. The authors also wish to
acknowledge the support of the U.S. Department of Education
through grant 99-ED-3928, the National Science Foundation through
grant 9860329 and the National Eye Institute through grant
1R43EY12470-01
Literature cited
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[2] J. Waymouth, Electric Discharge Lamps, MIT Press, Cambridge,
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[3] M. Dachs, "Optical Communication System,"'' U.S. Patent
#3900404, August 1975.
[4] K. King, R. Zawislak, and R. Vokoun, "Boost-Mode
Energization and Modulation Circuit for an Arc Lamp,"'' U.S.
Patent #5550434, August 1996.
[5] M. Smith, "Modulation and Coding for Transmission using
Fluorescent Lamp Tubes,"'' U.S. Pat.ent #5657145, August
1997.
[6] K. Uehara and K. Kagoshima, "Transceiver for Wireless
In-Building Communication Sytem [sic],"'' U.S. Patent#5424859,
June 1995.
[7] Buffaloe, T.K., D.K. Jackson, S.B. Leeb, M.F. Schlecht, and
R.A. Leeb, "Fiat Lux: A Fluorescent Lamp Transceiver,"'' Applied
Power Electronics Conference, Atlanta, Georgia, 1999.7
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