LCD & DLP Projection Technologies for
Digital Signage
In the real world, a customer won’t know the difference
between a DLP or LCD projected image, let alone want to know
what the terminology means. As long as it fits their budget
and produces a result, the customer is happy.
In the world of digital signage, it’s not that simple.
Running a projector for 8 hours per day, 7 days a week, the
customer will want a projector to last the distance, for at
least 3 years and be cost effective.
Moving on to 24/7 operation becomes more critical. There has
been much discussion on the benefits of each technology, but
when it comes down to operational expense it’s important
to do the right thing by your customers.
The easiest way to determine the suitability of a projector
for digital signage is to ask whether the manufacturers will
stand by their warranty period.
It has been our experience that you won't get a 2 or 3 year
warranty on an LCD projector if you will be using it for 24/7
operations.
The suppliers of DLP projectors are standing by their warranty
periods.
So what is the difference?
LCD - Liquid Crystal Display
LCD projectors consist of a red, green and blue LCD glass
panel corresponding with the image signal being sent by the
projector.
Light from the projector lamp passes through these panels
in individual pixels which can be opened to allow the light
through or closed to stop the light from projecting on the
screen. The process produces the image.
LCD Benefits:
1. Sharper image with text such as spreadsheets and charts,
no so much with video images.
2. Light efficient, higher ANSI lumens from the same wattage
lamp.
3. Better colour saturation, although DLP is catching up
quickly.
LCD Weaknesses:
1. Low black levels and contrast.
2. Pixilation - the screendoor effect - although this is
improving all the time.
DLP - Digital Light Processing
DLP technology is a proprietary solution from Texas Instruments
that uses an optical semiconductor to manipulate the light
digitally.
The optical semiconductor is known as the Digital Micromirror
Device, or DMD chip
The DMD chip is a sophisticated light switch. It is made
up of a rectangular array of up to 1.3 million hinge-mounted
microscopic mirrors, each measuring less than one-fifth the
width of a human hair.
When combining the DMD chip with a digital video signal,
the light source and a projection lens, the mirrors can reflect
an all-digital image.
The light generated by the lamp in a DLP projection system
passes through a colour wheel as it travels to the surface
of the DMD panel. The colour wheel filters the light into
red, green, and blue, from which a single-chip DLP projection
system can create at least 16.7 million colours.
The on and off states of each micromirror are coordinated
with these three basic building blocks of colour. For example,
a mirror responsible for projecting a purple pixel will only
reflect red and blue light to the projection surface.
The DMD and associated electronics creates the overall technology
known as Digital Light Processing technology.
DLP Benefits:
1. High Black Levels and Contrast
2. Compact size
DLP Weaknesses:
1. Potential rainbow effect. Hard to pick and almost eliminated
Long Term LCD Problems when used for Digital Signage
A laboratory test conducted by Texas Instruments highlighted
a failure in LCD technology that doesn't exist with DLP.
The tests showed that over time, the blue LCD panels degrade,
causing a shift in colour balance and a reduction of contrast
overall.
Of course we must take in to account that this test was conducted
by Texas Instruments although held independently at the Munsell
Color Science Laboratory (MCSL) (www.cis.rit.edu/research/mcsl),
at the Rochester Institute of Technology.
The LCD projector issue hasn't been denied by LCD distributors
and known installations have indeed failed, requiring the
replacement or repair of LCD's under warranty
LCD manufacturers recognise that the organic compounds in
the LCD panels and polarisers are susceptible to heat and
light energy stress and will eventually break down - in particular
24x7 operation.
Compact portable LCD projectors are not recommended for digital
signage because of this.
Conclusion
The digital signage usage, DLP projectors win over LCD projectors.
If you are still not convinced, make sure you'll receive your
full warranty when using an LCD projector for digital signage.
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