Illumination – Plural light sources – Particular wavelength
Reexamination Certificate
2000-05-24
2003-03-25
Sember, Thomas M. (Department: 2875)
Illumination
Plural light sources
Particular wavelength
C362S812000, C362S800000, C362S249070
Reexamination Certificate
active
06536913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an LED display apparatus. More particularly, the present invention relates to an LED display apparatus that is adapted to be installed on a place where it can be directly touched by a hand of a user.
2. Description of the Related Art
There have been widely used display apparatus in which a plurality of light-emitting portions using LEDs (light-emitting diodes) as display devices are arranged in the form of segments or a matrix to constitute a display element, as well as display apparatus in which a plurality of display modules each being formed by matrices of light-emitting portions are arranged like tiles.
Most of these conventional display apparatus (referred to as “LED display devices” in this specification) have large pixel pitches (pitches among the individual light-emitting portions) and, hence, offer low resolution.
Therefore, the LED display devices that display images upon receiving video signals must be watched from a visual regognition distance and are, hence, generally installed outdoors, such as on a wall of a building where they cannot be directly touched by human hand.
Recently, however, there has been proposed an LED display device having a small pixel pitch so that it can be watched from a short visual recognition distance, suggesting increasing chances for installing the LED display devices for displaying images on a place where they can be directly touched by human hand in the future.
When the LED display device is installed on a place where it can be directly touched by human hand as described above, there arises a probability that, when the human hand approaches the display surface, an electrostatic discharge may take place between the electrically charged human body and the LED display device that is grounded, and an electric current may flow into the light-emitting portions and the driving ICs due to the electrostatic discharge, resulting in a malfunctioning or breakage of the light-emitting portions and the driving ICs. Therefore, the LED display device installed on such a place requires a countermeasure against damage caused by static electricity.
As one of the countermeasures, it has been attempted as shown, for example, in
FIG. 5
, to attach louvers
11
which are protrusions extending in a Z-direction in
FIG. 5
among the rows of light-emitting portions L arranged like a matrix on the display surface of the LED display device.
By arranging the louvers
11
, positions close to the light-emitting portions L inside of the louvers
11
are not accessible by human hand; i.e., a predetermined distance equal to a difference between the height of the louvers
11
and the height of the light-emitting portions L is maintained between the human hand and the light-emitting portions L.
Due to this distance, it is difficult that the current of electric discharge flows into the light-emitting portions or into the driving ICs despite of the occurrence of an electrostatic discharge, lowering the probability of malfunction or breakage in the light-emitting portions and the driving ICs.
According to another countermeasure as shown in, for example,
FIG. 6
, the whole display surface of the LED display device is covered with a transparent protection film
12
. By covering the display surface with the protection film
12
, a predetermined distance is also maintained between the human hand and the light-emitting portions L. Even when an electrostatic discharge occurs, therefore, the current of electric discharge does not flow to the light-emitting portions and the driving ICs.
There has been proposed a further LED display device in which the light-emitting portions are mounted on a base plate, such as circuit board, with their lead portions (connection terminals) being exposed.
FIG. 7
illustrates an example of the light-emitting portions of this structure, wherein LED lamps
31
of the shape of a bullet are mounted on the LED base plate
32
with the lead portions
31
a
being exposed. In the LED display device having such LED lamps
31
, a current due to the electrostatic discharge flows from the lead portions
31
a
into the LED chips in the LED lamps
31
and into the driving ICs on the LED base plate
32
, causing a malfunction or a breakage in the LED lamps
31
and in the driving ICs.
In this LED display device, therefore, it has heretofore been attempted, as shown in
FIG. 7
, to drip a thermosetting silicone resin (or an urethane resin, etc.)
34
from the upper side of the LED base plate
32
contained in a cell case
33
to prevent the leakage of the resin, thereby to seal the lead portions
31
a
with the silicone resin
34
, as a countermeasure for preventing damage due to static electricity.
By sealing the lead portions
31
a
with the silicone resin
34
as described above, the current caused by the electrostatic discharge does not flow into the lead portions
31
a,
lowering the probability of malfunction or breakage in the LED lamps
31
and in the driving ICs.
When the protuberances such as louvers protruding forward beyond the light-emitting portions are attached on the display surface as shown in
FIG. 5
, however, the light-emitting portions are shielded by the protrusions and cannot be seen when the display surface is watched from an upper inclined direction or from a lower inclined direction. Thus, the protuberances such as louvers narrow the visible angle and worsen the visual recognition particularly when the LED device is installed at a close distance so that it can be directly touched by human hand.
Further, when the display surface is covered with the protection film as shown in
FIG. 6
, the external light (sunlight when the display device is installed outdoors, or light of illumination when the display device is installed indoors) is reflected by the protection film, whereby the surrounding scenery is reflected on the display surface and light from the light-emitting portions is partly absorbed by the protection film lowering the brightness. In this case, too, therefore, the visual recognition to the LED display device is worsened.
Thus, the countermeasures employed in the examples of
FIGS. 5 and 6
are accompanied by such an inconvenience as worsening the visual recognition to LED display device.
Besides, the protection film employed in the example of
FIG. 6
is generally expensive driving up the cost of producing the LED display device of a large screen.
Moreover, even when a predetermined distance is maintained between the human hand and the light-emitting portions by attaching the protrusions such as louvers or by covering the display surface with the protection film as done in
FIGS. 5 and 6
, the current due to electrostatic discharge often flows into the light-emitting portions and driving ICs over the distance when the potential difference is great between the human body and the LED display device.
Thus, the conventional countermeasures are not capable of reliably preventing damage due to static electricity.
In the case of sealing the lead portions of the LED lamps by potting as shown in
FIG. 7
, large machining cost and material cost are required for potting, driving up the cost of production.
Further, when the lead portions are sealed with the silicone resin, it becomes difficult to remove the light-emitting portions from the LED base plate. Therefore, in case that some light-emitting portions are found defective in the maintenance after the production, the whole base plate including the light-emitting portions (the whole cell case
33
containing the LED base plate
32
in the example of
FIG. 7
) must be replaced, resulting in an increase of the cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an LED display device which is capable of preventing damage caused by static electricity and of reliably preventing damage caused by static electricity without worsening the visual recognition.
The LED display device of the present invention comprises:
at least one panel having LEDs arranged in the form of a matrix
Murata Masahiro
Takahashi Hitoshi
Yajima Akihito
Maioli Jay H.
Sember Thomas M.
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