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Vibrant & Dynamic

Perhaps the best words to describe the benefits of LED technology are dynamic and vibrant. Most LCD digital signage screens or standard advertising billboards could be described as passive and dull in comparison to LED screens or billboards. LCD screens have a standard brightness of 800 candela per sq. metre, which renders them unsuitable for outdoor viewing. Even the lowest brightness LED screen will be 1500 cd/m2 (or NITS) and many will go as high as 10,000 cd/m2. Light from a projector is measured in ANSI Lumens which is a measurement of light reflected and is much less powerful than the brightness of LED screens. A quick test to prove the point – look directly at a light bulb and then look at it reflecting off a white surface – it is much weaker. In fact, a 5000 NIT LED screen would be approximately 3.5 times brighter than a 5000 lumens projector, which is a very powerful and expensive projector.

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Advertising Multiplier

Passers-by will, generally speaking not be attracted to looking at a low brightness static image. Hence the importance of standard advertising sites being in head-on locations such as the top of elevators where the captive public cannot but see the advertisement. Because of the vibrancy and dynamism of LED video billboards the location and hence the higher expense is not as essential, because the image comes out so powerfully that the human eye is attracted immediately to the site, even from long distances. In addition, because of the ease of changing the image every few seconds or playing video the human eye is again attracted to the changing vibrant image – thus increasing the advertising value of any site manifold.

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Crowd Gripper

Public Houses and Hotels spend heavily on installing LCD televisions and large projection screens but the public has tired of the small ‘big screen TV' which they can now have so readily in their living rooms – why go to the pub to watch the big game when you can watch it in the comfort of your armchair? Over the past decades many pubs have installed powerful projectors to draw the crowds for large sporting events but projection has two problems – generally speaking low brightness and so it tends to be a passive medium, and unless the room can be darkened they operate very poorly in daytime. Big LED TV screens have an ability to grab the crowd, creating a much more lively atmosphere indoors in a pub or outdoors in a beer garden or smoking area. No matter what time of day or how bright the sun the big LED TV screen will draw the crowd and keep them gripped for the duration of the game.

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LED Technology Options

The right type of LED screen or video-wall for your purposes can be calculated according to the following variables: INDOOR OR OUTDOOR - BRIGHTNESS - VIEWING DISTANCE - PIXEL PITCH

Indoor LED screens will generally not require a brightness above 1500 candela per sq. m and do not require weather proofing.

Outdoor LED screens will normally require a brightness of 5000 candela per sq. m and will require weather proofing on one or both sides.

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BRIGHTNESS

A major factor in the impact of LED screens is the brightness of the image, which they can output – thus grabbing the attention of even the casual viewer. Brightness is usually measured in candelas per sq. m or NITS. A small LCD screen may have a brightness level of 250 cd/m2 or a 42” LCD 800 cd/m2. An indoor LED screen would normally have a brightness of 1500 cd/m2 whereas a large outdoor LED screen could have a brightness of 10,000 cd/m2.

What brightness do you require? This brings us to the question of:

VIEWING DISTANCE

Perhaps most readers will be familiar with LED screens from large sport stadia where the viewing distance might average 70m. Such a viewing distance would require a brightness of 10,000 cd/m2 so as to be visible at the extremities of the stadium and to cope with the brightness of daylight or floodlighting.

A viewing distance of 10 m would only require a brightness of 5000 cd/m2 and in duller environments this could be reduced to 3,000. LED displays can be fitted with automatic brightness adjusters.

Viewing distance also determines the size and density of the LED required:

PIXEL PITCH

LED screens are made up of clusters of small Light Emitting Diodes (LED) each consisting of 2 red 1 green 1 blue diode. A normal TV picture is made up of an array of pixels, which change brightness and colour to give us the image. A HD LCD TV will have 1366 (horizontal) x 768 (vertical) pixels. To get a very good quality picture with an outdoor LED screen at 10 metres viewing distance one needs a video-wall of approx. 3 metres x 1.5m with a pixel pitch of 10mm – that is the distance from the centre of one LED unit to the centre of the next. This would give a pixel density or resolution of 300 x 150. A P10 LED screen of size 20m x 12m would give a resolution of 2000 x 1200 pixels = the equivalent of a full High Definition picture on a normal television. Many advertising billboards would have a pixel pitch of 16 – 20 mm.

LED Pixel Pitch


VIRTUAL PIXELS

When looking at LED screen options one must be aware of ‘virtualisation' whereby some companies claim to have a higher resolution than they actually have (and at a lower cost). This claim is based on sharing the red of each LED with a neighbouring blue and green. This may work fairly well on very large screens at long distances but for most applications it is actually only using a quarter of the pixel density and loses out on clarity and colour to a very significant extent. LED Displays Ltd will always quote for ‘physical pixels' unless specifically required to quote for ‘virtual pixels'.

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