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The results, while not statistically representative, do
offer clear evidence of degradation problems and raise some
serious questions for makers and users of HTPS projectors.
DLP projectors showed little or no degradation.
Many projection companies already know there can be reliability
problems with HTPS panels, as these projectors cannot be
used in any 24/7 applications. This new data provides the
first public evidence of serious degradation issues in HPTS
projectors - particularly in the blue panel where the higher
energy is suspected of degrading the liquid crystal material,
alignment layer and polarizer.
TI revealed the data to an invited group of press and analysts
at its headquarters in Texas in mid-March. In addition,
DLP projector makers Optoma, BenQ, Plus and Dell were on
hand to confirm their intentions to provide this data to
customers. Noticeably absent were companies like NEC and
InFocus that have strong lines of both DLP and HTPS projectors.
These results will likely cause headaches for these and
many other companies.
The study was undertaken to see how DLP technology would
stand up to HTPS in a long-term reliability evaluation,
with the goal of obtaining objective data for evaluation.
While TI funded the study, it took a hands-off approach
to the collection of data, which was done by MCSL.
The study was begun in May 2002 with the selection of five
HTPS best-selling projectors and two DLP projectors. The
sample set featured projectors from different vendors (not
revealed) with different panel sizes, brightness specs,
weights and resolutions. All were placed in a dark room
and run continuously, with lamp changes as required. Periodically,
MCSL would measure the luminance, contrast, uniformity and
chromaticity of each projector. The following results and
conclusions were obtained:
· Full-field and ANSI contrast degraded over time
for all five HTPS projectors, but were steady for DLP projectors.
· The dark levels got brighter in HPTS projectors,
but remained steady with DLP.
· Brightness and uniformity remained basically unchanged
regardless of microdisplay technology.
· Color chromaticity changed significantly and erratically
in all five HTPS projectors.
· Optical performance deteriorated to unacceptable
levels in all five HTPS projectors, but was okay in the
DLP projectors.
· HTPS failures were due to panel degradation and
were not recoverable.
TI developed a term it calls picture reliability, which
it defines as the "time [SM1] to unacceptable picture
quality attributes to the light modulator subassembly."
This does not mean point defects or slight blemishes, but
the point at which a noticeable change in image quality
has occurred such that the user may not be satisfied with
the picture quality - a subjective point, for sure.
TI says that most of the HTPS projectors begin to fail
by exhibiting a subtle yellowing of the screen with a subsequent
blue blemish. Of the five HTPS projectors tested, this unacceptable
picture reliability point was judged to occur at 1368, 2180,
2353, 3456 and 3456 hours. After 4700 hours of testing,
the two DLP projectors had not yet reached this unacceptable
picture reliability point[SM2] .
The image on the left is
the DLP projector while the image on the right is from a
HTPS-LCD projector. The yellowing of the entire image is
the result of the failure of the blue panel.
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