Comparison of LCD displays and LED panels

The working principles of Information display technologies using a matrix of LED (Light-Emitting Diode) diodes and LCD displays (Liquid-Crystal Display) are very different. Both technologies have both advantages and disadvantages when used outdoors.

LED panel coloring – solutions

Display panels consisting of couple thousand LED are currently the most frequently used outdoor information display technology in public transportation. In the case of LED panels each diode acts as one displayable point on the information surface and corresponds with one “big” pixel on LCD displays. The ability of LED panels to display color depends on the type of LED diodes (multi-LED chip) and on the colors used. Unlike full color LCD displays, the ways of displaying using LED can be divided as follows:

1. Single color – usually red, yellow, green and white or in some cases also other colors. Suitable for displaying text and simple graphics with similar illumination of the whole panel. Sufficient for stop panels and signs. These panels are cheaper than LCD panels for outdoor use.
2. Two basic colors- usually a combination of red and green, or red and yellow, other combinations are also possible. It is possible to display three colors, the third color is displayed when both LED diodes emit light at the same time in one casing (e.g. red – green – orange). The price of such a panel is at least 50% higher than the price of the above solution. The color distinction allows passengers to easily tell apart e.g. trains, municipal transportation and regional transportation.           
3. Three basic colors - here we are talking about a standard fully colored triple LED diode, i.e. a multi-LED containing individual LED such as red – green – blue. In case of a cheaper solution individual colors are only fastened together and it is not possible to achieve a full color display. This solution is not used very often.
4. Three basic colors with full graphic control of illumination  – this solution is similar to the behavior of points on LCD displays but individual points have much higher illumination. This type of LED panels is suitable for outdoor use and it replaces LCD screens, however, it is more complex to control with separate regulation of illumination of each LED diode “chip” even in multi-LED. These panels are severalfold more expensive than corresponding LCD panels.

In the case of using single color LED panels it is only possible to display information consisting of individual signs belonging to the used set of signs (it is possible to modify some of the signs into simple pictograms to achieve a partly graphic effect). On the other hand, LCD displays are usually able to display at least 256 thousand colors or more.

Therefore in the case of LED displays it is better to concentrate on blinking of some of the fields if we want to highlight a text or a pictogram.  Thanks to “big” display points, inverse text displays can be more difficult to read.

Comparison of panel readability in full sunlight

Panels consisting of LED matrixes have very good observation angles especially when so called flat LED diodes are used. The observation angle of this diode type is practically 170° and more and it also has very good readability under any light conditions. LED panels are therefore suitable for both inner and outer use and even in direct sunlight.

LCD displays have a big disadvantage in comparison with LED panels when used in direct sunlight when display illumination is not able to “illuminate” the surface of an LCD display efficiently enough to achieve readability comparable with LED panels. Such readability cannot be achieved even with increased illumination, special optical “bandage” and sunfilters. Information displayed on an LCD display in direct sunlight is difficult to read from distance in the case of both negative and positive displaying of text. The pictures no. 2a and 2b were taken in direct sunlight at high noon (luminous flux of 100 000 Cd/m2), which is 100 x higher than high-illumination LCD display illumination. The reason for higher readability of LED displays in direct sunlight is very simple – even in case of current production technologies of high-illumination LCD displays, LED panels have approximately 20x higher brightness.

 LED panel readability in direct sunlight – is always good when a contrast foil is used

42“ high-illumination  LCD panel readability in direct sunlight at noon – the pictures were taken from the distance of 5 m (if the distance is longer displays are practically unreadable). LCD panel brightness during the test was 1150 Cd/m.

 Comparison of the lifespan of LCD panels and LED panels

Both LCD display and LED panel lifespan is significantly influenced especially by brightness intensity. All LCD and LED displays supplied by the Ing. Ivo Herman, CSc. company are equipped with an illumination sensor that regulates brightness to lengthen their lifespan and prevent unpleasant dazzling of people at night or in low surrounding light.

Since LED diodes have much higher brightness their performance is usually lowered while good readability is preserved and adapted to the surrounding light. This makes it possible for us to guarantee LED panel lifespan of min. 150 000 hours (given by voltage regulation in LED diodes).

The maximum brightness of high illumination LCD displays is still approximately 20x lower than LED panel brightness which brings a more frequent need of maximum brightness to ensure good displaying of information on the display. Because of the frequent use of maximum brightness display lifespan is lowered significantly. This also causes a frequent necessity of changing LCD displays (if there is a compatible model on the market), the change is needed approximately after 5 years, display electronic parts last much longer.

Demonstration of the light of a 42“LCD in different kinds of lighting

As shown in the picture no. 2 – even in the case of full brightness of an LCD display, sunlight is approximately 100x more intensive making LCD panels difficult to read.  For the reasons of completeness pic. no. 3 shows a situation when LCD panels are placed in the shadow while sunlight remains the same. According to the table no. 3, sunlight is approximately 10x lower in the shadow which ensures good readability of the displayed information even at high noon.

High-illumination 42“ LCD panel readability in the shadow behind a building (full sunlight in front of the building – no clouds), the picture was taken from the distance of  5 m. LCD panel brightness was 1150 Cd/m2 during the test – estimated surrounding light 10-12 thousand Cd/m2.

Comparison of parameters of comparable LED and LCD panels (approximately 42“)

It is clear from the preceding description that a LED panel has a lower number of displayable points (resolution) with similar active surface measurements. However, this does not prevent  displaying of texts with good readability even from the distance of more than 25 m from the panel. Compared with LCD displays LED panels have significantly higher maximum brightness that ensures high quality information displaying even in direct sunlight. The values in the LED panel and LCD display table are based on currently used and accessible technologies.

1000 – 1500 Cd/m² brightness is currently one of the highest values that can be found in LCD displays. For illustration, values used for standard notebook LCD displays or Pc monitors fluctuate between 200 and 350 Cd/m².

LCD displays with brightness values between 200 and 500 Cd/m² are completely useless outdoors. In direct sunlight such displays are completely black – completely unreadable and they can even be damaged by direct sunlight. Displays with brightness values higher than 900 Cd/m² stay partly readable from short distances.

Simply put advantages of LED in comparison with LCD:

• Higher brightness and therefore higher readability in direct sunlight
• Significantly lower average power consumption
• Significantly higher range of working temperatures
• Significantly longer lifespan of the panel
• Lowered maintenance of the panel

Table no. 1: Parameters of display units of comparable sizes

	LED panel 5 lines	42″ LCD
Graphic surface measurements	1000 × 300 [mm]	930 × 523 [mm]
Total graphic surface	0,3m²	0,48m²
Number of columns × number of lines	160 × 50	1920 × 1080
Number of light points	8000	2,0736 mil.
Point / pixel brightness	1,000 Cd	0,00027 Cd
Total panel / display brightness	26 680 Cd/m²	1150 Cd/m²
One point / pixel consumption	20mA	0,081mA
Total consumption – max. full ¹)	160W	180W
Total consumption – max. text ²)	40W	180W
Total consumption – night full	40W	90W
Total consumption – night text	10W	90W
Yearly consumption [kWh/year] ³)	157kWh	1184kWh
Temperature range	from -40°C to +100°C	From -0°C to 50°C
Lifespan [hour] 4)	150000 / 17 years	50000 / 5,7 years

1. maximum light at maximum illumination of all diodes
2. text illumination is approximately 25% of the active surface of the panel (energy is consumed only by illuminated points)
3. The consumption does not include the power consumption of the panel control unit. Here again LED panel control units have lower power consumption 2-5W than LCD panels with consumption of 5-10W and higher. The power consumption is permanent.
4. holds for the voltage regulation used in LED panels produced by Herman and for using OSRAM diodes.

In our opinion advantages of LCD displays in comparison with LED panels do not need to be stressed because they are generally known – full color display with a graphic surface, simple change of display and a fine point rastr.

LCD display construction parameters

LCD displays are also very different regarding their construction itself. Their construction is significantly more complicated than in the case of LED panels. The complicated panel construction is the main cause of problems in the production of large-area panels with a broadened brightness and working temperature range.

When the running temperature is low, additional display heating can be used or on the other hand during summer days display cooling must be used (forced ventilation). This solution is financially demanding regarding its purchase and it increases total energy expenses.

The second biggest problem is the solution of display illumination ensuring the highest possible brightness.  Even though LCD display technologies are still being further developed, currently it is not possible to get an LCD display with brightness values higher than 1500 Cd/m².

Working temperature range according to the size of the LCD display

1. Normal temperature range (from 0°C to +50°C): all LCD sizes
2. Broadened temperature range (from -20°C to +70°C): size up to 30“
3. Broad temperature range (from -30°C to +85°C): size up to 24“

Problems connected with supplying panels equipped with LCD displays

• Large LCD displays above 30“ are not produced with a broadened temperature range (it is necessary to provide both cooling and heating which brings an increase of expenses)
• The highest outdoor LCD display brightness is 1 200 Cd/m², for smaller displays 1 500 Cd/m²
• Outdoor LCD with increased brightness (above 500 Cd/m²) are much wider than standard displays (mechanical rendition) because they contain special sunlight filters
• LCD displays with increased brightness (above 500 Cd/m²) are severalfold more expensive than standard displays with the  brightness of up to 350 Cd/m².

Table no. 2: Properties of individual components of an LCD display.

LCD parts	Material	Temperature data	Consequences of high temperatures
Polarization film	PVA, TAC, PET	80°C, 500 hours
Glass with a color filter	Glass	No restrictions	NA
Liquid crystals	Widened temperature range	from -35°C to 95°C	Dim-out – renewable
	Standard temperature range	from -20°C to 75°C	Dim-out – renewable
Polarization film	Glass	80°C, 500 hours	NA
Optical film	PVA, TAC, PET	< 85°	Rippling of the picture – irreversible
Light conducting board	PVA, PET	< 95°	Deformation – irreversible
Plastic frame	PMMA (plastic)	< 95°	Deformation – irreversible
Light source	LED	from -35°C to 85°C	Shortening of lifespan at high temperatures
LED controller	IO	Depends on its construction

Comparison of technologies

The table number 3 contains brightness values according to various environments which can be compared to brightness values of both display technologies. According to the above pictures of an LCD display and its parameters and to the comparison with the brightness table, it is not good that LCD displays are more suitable for outside covered spaces protected against direct sunlight because even if high-quality optical filters are used, it is not possible to achieve readability in direct sunlight comparable with the readability of LED panels.

LCD displays are suitable for indoor spaces and for outdoor spaces protected against direct sunlight.

LED panels are suitable for places unprotected against direct sunlight where the sun will shine at the display for most of the day and where the display should be readable from greater distances (10 meters and more).

In the next table we provide illumination values to ensure completion of the description:

Table 3: Illumination values in various environments.

Light source	Illumination (L [cd/m²])
Illumination at night with full moon	0,2
Illumination for comfortable reading	50
Office illumination	300
High quality illumination in a room	700
Sunlight, an hour before sunset	1 000
Daylight, overcast	3 000
Sunny day in the shadow of a tree	10 000
Direct sunlight at noon	100 000