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| 型號(hào)： | ISD2353 |
| 廠商： | Osram Opto Semiconductors GmbH |
| 英文描述： | Sunlight Readability Contrast Measurements |
| 中文描述： | 日光可讀性對比測量 |
| 文件頁數(shù)： | 1/4頁 |
| 文件大?。?/td> | 146K |
| 代理商： | ISD2353 |
www.infineon.com/opto 1-888-Infineon (1-888-463-4636)
OSRAM Opto Semiconductors GmbH & Co. OHG Regensburg, Germany
www.osram-os.com +49-941-202-7178
2000 Infineon Technologies Corp. Optoelectronics Division San Jose, CA
1
May 31, 2000-14
Introduction
Light emitting diode alphanumeric displays have had a long and
successful relationship with military and avionic equipment.
Applications with very high light ambients now are possible
because of advances in the efficiency of LEDs. Polarized filters
enhance the readability of LEDs by eliminating much of the ambi-
ent reflection from the LED die and the surrounding package.
Readability Criteria
An observer's ability to perceive the information from an alpha-
numeric display depends on two factors. These include font
and size of the message in relationship to the viewing position
and the optical contrast of the message to the surrounding
environment.
Optical contrast is the comparison of the brightness or sterance
(L) of the On/Off/LED to the brightness of the surrounding envi-
ronment. High readability results by optimizing the following
contrast ratios. The first ratio, C
1
ance, L
LEDon
, and the background stearance, L
when the OnLED is brighter than the surrounding area. Thus C
will be much greater than unity (1).
The next ratio, C
2
, involves the sterance ratio of the On,
L
LEDon
, and Off, L
LEDoff
, LED. C
2
is much greater than the L
LEDoff
greater than unity (1).
The optimal ratio of C3, involving OffLED to the background, is
achieved when the ratio is near zero. The OffLED should have
minimal contrast with the background.
, involves the OnLED stear-
B
, is optimized
1
is optimized when the L
, resulting in being much
LEDon
The equations for these three ratios are given below.
The U.S. military has established contrast ratios limits to satisfy
sunlight readability criteria. These criteria are published in,
”
Night Vision Goggle Lighting Specification.
are shown below:
C1—OnLED to Background
C2—OnLED to OffLED
C3—OffLED to Background
” The specifications
≥
≥
≤
2.0:1 Minimum
2.0:1 Minimum
0.25:1 Maximum
Optical Filtering
An LED, regardless of its brightness, has a difficult time com-
peting with the sterance of the sun. An LED display’s readabil-
ity can be greatly improved by using contrast enhancement
filters. The filter of choice is one that eliminates the interfer-
ence of the sun with the background of the display. A number
of filter vendors offer anti-reflection coated, circular polarized
(AR/CP), optically tinted bandpass and neutral density filters
which have proven very helpful in satisfying the sunlight read-
ability contrast requirements.
The display front surface and the areas surrounding the LEDs
have specular reflector characteristics. This reflective property
allows optimum contrast when used with a circular polarized fil-
ter with anti-reflective coating. See Table 1 for Filter Selection
Guide.
Sunlight Readability
Contrast Measurements for
the ISD2351 and ISD2353
Serial Input Small
Alphanumeric Display
Appnote 47
by Bob Krause
Ratio Equations
1) C
1
—OnLED to Background
L
B
2) C
2
—OnLED to OffLED
3) C
3
—OffLED to Background
C
1
L
B
–
-------------------------------
=
C
2
L
--------------------------------------------
L
–
LEDoff
=
C
3
L
---------------------------------------
L
–
B
=
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