Signage display, which is used to convey message or information, has evolved from conventional to digital display. Conventional signage which may be hand written or printed papers are being wiped out by digital displays used by industries because of its attractive features of efficient involvement of consumers. However, extensive use of digital signage displays contributes a notable amount of power consumption (about 1000W for a 14inch × 48inch display) of a region. In this literature, we have devised a novel approach for reducing power consumption of digital signage as well as satisfying human visibility by exploiting duty cycle. Our proposed technique is capable of relinquishing a significant amount (about 14.54% in comparison with existing display system) of power consumption occurred by digital display by keeping an eye on expected human vision.

1. Towards Greening the Digital Display System
Tarik Reza Toha1, Salman Estyak2, Md. Abdullah Al Alamin3, Md. Hasanul Islam4,
Md. Abdullah Al Maruf5, Swarnendu Saikat Nandi6, Amit Chakraborty7, and A. B. M. Alim Al Islam8
Department of CSE, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh
Email: 1tarik.toha@gmail.com, 2salman.estyak@gmail.com, 3mdabdullahalalaminp@gmail.com, 4hasanuli10@gmail.com,
5ropymaruf2010@gmail.com, 6saikat.buet.cse@gmail.com, 7amitchakraborty074@gmail.com, and 8alim_razi@cse.buet.ac.bd
Background
•Digital displays stand for modernization of city and
digital era
• It has versatile applications such as displaying information
on electronic equipment and instrument panels,
advertisements on billboards, etc.
•The display is one of the components in an electronic
device, which has the highest percentage of total
energy consumption [1], [2]
• The study in [3] concludes that a digital billboard can
consume up to 30 times the energy that an average
American home uses in a year
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Proposed Methodology
•While displaying a character on a LED dot matrix by
row-wise, we have to select a single row in every
frame period to print the corresponding pattern of that
frame
• Thus, every frame period requires power to display the
frame
•By pausing the row selection for a small portion of a
frame period (say, the duty cycle is 95%), the
brightness of the display does not decrease
significantly
• This technique reduces the total power consumption of a dot
matrix display system for the dimming period
•Additionally, we can green the digital display system
by decreasing the system frequency and frame period
in exchange of brightness
Experimentation and Findings
•We investigate the impact of duty cycle change on
luminous efficacy in a 2 x 4 dot matrix display
module
• We use shift registers and
Darlington transistor arrays
in order to reduce the total
power requirement of our
display module
Conclusion and Future Work
•We attempt to reduce the power consumption of a
LED dot matrix display system by varying all
possible parameters such as duty cycle, frame rate,
and system frequency
•We found that the optimal point is 85% duty cycle,
50 Hz frame rate, and 16 MHz system frequency,
which keeps the display aesthetic enough
•We plan to find more contributing factors of the LED
display system such as LED temperature, etc., which
will lead the system greener
References
NSysS 2017, January 5-8, 2017, Dhaka, Bangladesh
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Motivation
•According to the U.S. Department of Energy, the
luminous efficacy (lumens per watt) of a Light
Emitting Diode (LED) is much higher, i.e., produces
more light than the traditional fluorescent,
incandescent, or halogen bulbs [3]
• The power hungriness of a LED display system such as dot
matrix display is still higher than any other components of
an electronic device [4]
•Dimming LED sources is an approach to enable power
saving [5]
• Pulse width modulation (PWM) operation, i.e., varying the
duty cycle is selected as the best dimming strategy [6], [7]
•However, greening the dot matrix display, the most
popular LED display system, by means of varying the
duty cycle is yet to be addressed in the literature
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Figure: The snapshot of our
display module
Figure: Duty cycle vs luminous efficacy per unit area while system
frequency is 16 MHz and 8 MHz respectively
• Summary of findings:
‒ With the decrease of duty cycle, system frequency, and
frame period, the illuminance decreases
‒ The minimum frame rates after flickering starts are 50 Hz
and 100 Hz for 16 MHz and 8 MHz system frequency
respectively
‒ The maximum efficacy per unit area have been achieved
when the duty cycle is 85% and 60% respectively
‒ At maximum efficacy per unit area, the amount of power
savings are 14.54% and 40%, and the brightness are
decreased by 12.5% and 37.5% respectively
• Although the overall maximum efficacy has been
achieved at 8 MHz system frequency, we can ignore it
because of its low illuminance