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.
