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Typical Parameter Values of the Different Technologies

	LED (active)	LCD (transflective)
Contrast	15:1	50:1
	Lower contrast in direct sunlight (High performance and bright LEDs have a shorter service life.)	Illumination from the front (in direct sunshine: reflective) and/or from the rear (backlighting)
Reading Angle	5° - 90° (type dependent)	140°
Character Luminance (monochrome)
Indoor Display	200cd/m²	200cd/m²
Outdoor Display	4500cd/m² (at 5°-10°)	1000-5000cd/m² (depending on structure)
Power Consumption
Indoor Display	4500W/m2	<250W/m2
Outdoor Display	>5000W/m2	<600W/m2
Efficiency	< 25Lm/W	< 40Lm/W
Filling Factor (Pixel Spacing)	ca. 30%	ca. 85%
Useful Service Life
Indoor Display	5 - 100.000h	> 200.000 h
Outdoor Display	< 50.000h	> 200.000 h
MTBF for one display element (444 Pixels)	100.000 h	> 2.000.000 h high reliability

General Information about LCD / LED Displays

Today, electronic display boards are state-of-the art technology. You can find this technology used in a wide range of applications, for example, in train stations, airports, public transportation vehicles and facilities, parking control systems, and time and temperature displays, as well as more recently in information display boards of cities, public authorities and corporations. They offer reliable and rapid information communication to the desired target groups. The question is repeatedly asked, which technology should be used to communicate this information. Here, we would like to give you a few facts about LCD / LED display boards.

Characters

90% of today's information is communicated in writing with the words displayed in print-like form. Reading means comparing the data seen with the information already stored in one’s memory. You read entire words or parts of sentences. That is why it is especially easy for a viewer to read the print-like characters of an LCD display.

• LCD: The LCD characters have a closed, print-like shape with straight and rounded corners.
• LED: As a rule, LED light-emitting diode displays are composed of point matrix areas. The letter shapes must be forced into the existing matrix, which sometimes produces abnormal and unaesthetic shapes as well as frayed character edges.

The LCD offers the viewer the advantage of very good readability even under the most unfavorable viewing angles. A point matrix appears unusual to a user and is therefore significantly more difficult to read. The degree of reading difficulty increases the closer the viewer is to the display.

Character Colors

• LCD: There are almost no limits regarding the choice of colors, as the LCD is always backlit by white light. A wide variety of colors can be produced by placing a color filter between the LCD and the backlighting.
• LED: LEDs are available for professional applications in red or yellow. Additional colors are also available, but are only used in the advertising sector, not in the traffic sector.

Outdoor Applications (and installation sites with high brightness > 30000 lx)

• LCD: The LCD as a transflective display utilizes the surrounding brightness in this application and offers excellent readability even in direct sunlight.
• LED: As an active medium the LED is at a disadvantage under direct sunlight. As a rule, high performance LEDs with a restricted emission angle are used in such applications.

Long-term Performance

• LCD: The age-dependent component of an LCD display board is the fluorescent tube. When it is replaced the original brightness of the LCD display is restored. LCDs show a transmission reduction of only 1-2 % during a 10-year operation period.
• LED: The LED as an active element loses luminance over time (depending on the intensity of use). LEDs can lose up to 30 % of their luminance during an operation period of 10 000 hours (= ca. 1.5 years).

The luminous area of an LCD is determined by 2 factors: the transmission of the LCD and the brightness of the fluorescent tube (behind the LCD). In practice, a reduction in the character brightness is solely caused by a reduction in the brightness of the fluorescent tube, as the transmission of the LCD remains constant over many years. By replacing the fluorescent tube of the backlighting, the original brightness of the LCD display can be restored.

However, as the LED is an active element, the basic brightness of the individual pixels declines during the time of use. If, for example, a digit field at one position of the LED display board is used to display changing information, then some LEDs are always on, some LEDs are on for a single time and the remaining LEDs only on for a period of time. The LEDs which are always on become darker because of the usage over time. Thus, the problem with the torn character shapes is made worse by the varying brightness of individual points. As a result, the readability is not very good.

A consistently bright luminous area during the useful life time of a display ensures the constant quality of the character face of the display and significantly increases the utilizability of such a display.

Service and Maintenance

• LCD: The LCD display boards are composed of individual modules. Thanks to the separation between the display and the backlighting (standard fluorescent tubes), service can be performed on an LCD display without the need for qualified personnel.
• LED: LED modules must be replaced as complete units.

Without considering the length of the useful service life, the spare parts costs of both technologies are about equal.

Cost Comparison of LED and LCD Technologies

• Display Configuration
• Outdoor Use / 24 Hour Operation
• Energy Costs: Example: Format: 5000x1800 mm (WxH) = 9 m2
• Electricity Cost per m2 / year: € 0.18
• LED ca. € 60,000 / LCD ca. € 5,000 per year

Spare Parts Costs

• LCD: Only the fluorescent tubes must be replaced approx. every 2 years. The display can still be read without backlighting in sunlight. The LCD glass panes themselves have a useful service life of ca. 22 years (MTBF > 2 000 000 h = reliability)
• LED: The complete digits must be replaced approx. every 5 years. (Brightness of each diode is dependent upon its actual operating time.). The display can hardly be read in sunlight. The useful service life of the LED diodes is currently a maximum of ca. 10 years, but the half life period is now 3 to a maximum of 5 years.

Service

• LCD: quick repair by owner (fluorescent tube)
• LED: repair by qualified service personnel (consider spare parts delivery time and need for a date for on-site service)

Displays	Investment Costs	Operating & Maintenance Costs / Year *
LED	100,000 €	8,820,- €, 8,8% of the investment costs
LCD	150,000 €	3,000,- €, of the investment costs
* Electricity costs not included

pros and cons

LED technology

• Advantages
• Short image change interval (image sequence display capability)
• Graphic display capability w/ new technology (256 colors)
• Low initial installation costs
• Cost-effective medium for large surface displays
• flexible handling
• Sale of display use for advertising possible
• Character ticker display capability
• Character positioning over the entire matrix surface

• Disadvantages
• Differing loss of luminance of the individual LEDS of a display board (nonuniform character face)
• Poor visibility in direct sunlight (phantom images)
• High energy consumption (4-5 kW/m2)
• Active display medium
• Limited reading angle - ca. 30° with outdoor type LEDs
• Low character resolution (only dots visible if closer than 5 m). Small characters can hardly be displayed
• A LED is physically extinguished when only 50 % of the original brightness is still available. This value is reached after ca. 50 000 operating hours.
• Partial flaring at night (too bright)
• No reflective component
• High operating and maintenance costs, due to nonuniform brightness if one segment is replaced

LCD technology

• Advantages
• High character resolution (print-like character face), Very good readability
• Low power requirement (power requirement dependent on the backlighting e.g. of the fluorescent tubes)
• Low energy costs, high efficiency, low dissipated heat
• High reliability - MTBF > 1 000 000 h
• Long useful service life, no aging losses
• Very good contrast
• Very rapid image change
• Illumination from the front and/or from the rear (transflective), active display medium combines the advantages of both types. Daytime - passive mode. Nighttime - active mode.
• Thin construction
• Extremely wide viewing angle range up to ca. 140°
• High operational reliability; easy maintenance and service
• No reflections on the surface
• Emergency operation possible in case of lamp failure (can be operated strictly in the reflective mode)
• Individual or all characters can blink or be underlined
• Ticker characters in columns (with pixel and proportional characters)
• After exchange of a fluorescent tube after ca. 2 years, display appearance is “like new”. No problems with differing character brightnesses.

• Disadvantages
• Graphic capability only with pixel cells or limited capability with proportional characters
• Limited character ticker capability
• Characters are line-oriented with segment and proportional characters
• Character size is module or glass dependent
• LCD price dependent on glass surface

Outdoor Display Technology Comparison

(Excerpt from the Professional Magazine "Straßenverkehrstechnik" (Motor Vehicle Traffic Technology) 11/98)

During the course of the preparation of this article, great attention was given to the selection of the freely programmable display technologies. Various technologies were evaluated and compared with one another. A comparison thereof is shown in the table below.

Freely programmable displays were defined as the basic requirement for the reasons previously stated. As a result, in this case, only two display technologies optimally fulfill the requirements of an outdoor application.

The LCD technology with a high quality glass pane was finally selected as the preferred technology. This product combines the advantages of high readability with low wear and tear, and therefore offers very low maintenance costs during the next 10 years.

	Fiber Optics Technology	7-Segment Technology	Prisma Technology	DOT Matrix (Tilt Elements)	LED	LCD
Display Recognizability
Information Content / Maintenance	free / occupied accessible	numbers	free / occupied accessible	freely progr.	freely progr.	freely progr.
Readability in sunlight	+ +	+ +	+ +	+ +	---	+ +
Readability at night	+ +	w/ interior illumination	w/ interior illumination	w/ interior illumination	+ +	w/ interior illumination
Multicolor Capability	+	---	o	---	+ +	---
Reliability
Useful Service Life	+ +	+ +	+	---	o	+ +
Failure Probability	+	+ +	+	+	---	+ +
Feedback Capability	+	+ +	+ +	---	---	+ +
Outdoor Use	+ +	+ +	+ +	+ +	---	+ +
Cost-effectiveness
Investment Costs	o	+ +	+ +	o	---	o
Operating Costs	o	+ +	+ +	+ +	---	+ +
Note: Scale from + + (very good) to --- (very poor). Only high quality display systems were evaluated.