Choosing A Display
Types of Display & Applications Viewability & Legibility Programming



      Part of the equation towards ensuring your display can be seen is the brightness. It is important that the display is bright enough to be seen in the expected light conditions and at the same not so bright that it blinds people.

      The brightness of LED based signs in usually measured in terms of milliCandelas (mCd), beware that this measurement refers to the brightness of each individual LED, it follows that two displays using the same brightness LED's but with different  LED densities will have a different impact overall.

      As a guide, make sure your display approximately conforms to the following recommendations (adjust the figures accordingly for a 'louder' or more discreet display):

        Internal - low ambient light (night club) 10 - 100 mCd
        Internal - normal ambient light (reception, office area) 100 - 300 mCd
        Internal - window usage 300 - 1000 mCd
        External - Never faces the sun 600 - 2000 mCd
        External - Facing the sun at some point during the day 1000 - 6000 mCd and more
      The brightness of full colour animation screens is measured in NITs because each pixel uses several different coloured LED's of varying brighness. NIT is a method of measuring the brightness of a surface area which means that it gives a true measurement of 'impact' and also allows comparison to other display types i.e. plasma, CRT, candescent bulb etc. The actual definition of NIT is candelas (not milliCandelas) per square metre. The following table gives an idea of different NIT measurements.
        Computer Monitor 100 NIT
        Plasma Display 400 NIT
        Television 400 NIT
        Video wall using large rear projection cubes 1000 NIT
        Video wall using small rear projection cubes 2000 NIT
        Indoor LED video display 1000 - 2000 NIT
        External LED video display 4000 - 7000 NIT
      Another subject related to brightness is contrast ratio. This is defined as the ratio between the brightness of the display when lit and un-lit. The higher the contrast ratio, the better the display. The main factor which affect the contrast ratio is natural light reflecting off both the display fascia and the actual LED's themselves. Dynamic Display use several techniques to enhance contrast; 'sun visors' over individual pixels, fascia's coated with diffuser, LED's / boards angled slightly downwards, LED boards treated with a proprietary matt surface.


      At least as important as display brightness is the size of the characters / images you wish to display set against the expected viewing distances.

      The main determining factor in how legible a character is at a given viewing distance is the amount it takes up in your field of view. The measurements associated with field of view calculations are quite small so the angles are measured in a fraction (1/60) of a degree known as a minute. For text to be legible it's height needs to form a minimum of 10 minutes, for optimum viewing around 20 minutes is recommended to be comfortable to read, for impact around 30 minutes and upwards is needed.

      The following table is a good guide to the viewing distance for a range of popular character heights.
      Character HeightSquinting!OptimumImpact
      12.5mm / 0.5"8.6m / 28'4.3m / 14'< 2.9m / 9'
      20mm / 0.8"13.8m / 45'6.9m / 23'< 4.6m / 15'
      25mm / 1"17.2m / 56'8.6m / 28'< 5.7m / 19'
      30mm / 1.2"21m / 68'10m / 34'< 7m / 23'
      50mm / 2"34m / 113'17m / 56'< 11m / 38'
      75mm / 3"52m / 169'26m / 85'< 17m / 56'
      100mm / 4"69m / 226'34m / 113'< 23m / 75'
      150mm / 6"103m / 339'52m / 169'< 34m / 113'
      200mm / 8"138m / 451'69m / 226'< 46m / 150'
      300mm / 12"206m / 677'103m / 339'< 69m / 226'
      500mm / 20"344m / 1129'172m / 564'< 115m / 376'
      800mm / 32"550m / 1806'275m / 903'< 183m / 602'
      1000mm / 40"688m / 2257'344m / 1120'< 229m / 752'
      1500mm / 60"1031m / 3386'516m / 1693'< 344m / 1129'
      2000mm / 80"1375m / 4515'688m / 2257'< 458m / 1505'



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Copyright 1998-2004, Dynamic Display Ltd. Last Modified: 27th December 2004