How bright should a digital signage screen be?

When you plan to make use of digital signage and are wondering what screens to use there are a number of aspects that you should consider. The most obvious one is the size of the screen. How to choose the best screen size is the subject of a previous blog post. A second factor that you should consider is the brightness of the screen because that can have a bigger influence on the price and running costs of the screen. This article will explain what brightness is, what things you should consider in choosing a screen and includes a table of what screen brightness to best use in typical environments where digital signage is used.

First things first

To understand the rest of this article and most screen vendor documentation it is necessary to briefly define what we mean by "brightness" and "illuminance":

  • brightness (also called limunance) is a measure of how much light is reflected or emitted from an object (screen), it is expressed/measured in "nits" (which is the same as cd/m2)
  • illuminance is a measure of light that is emitted from all light sources in a room/location - lamps and/or the sun - so called ambient light. You see this light when it reflects off an object. Illuminance is measured in lux (lx for short or lumen/m2 or lm/m2 for short).

In short; the measure for the light coming from a screen is called brightness and the measure of how much light there is in a space is called illuminance. It makes sense that in order for content on a screen to be visible it has to be brighter than objects around it (which are illuminated by the ambient light).

What determines the right brightness

The "right" brightness of a screen is the brightness that is enough to make the content of the screen overcome the brightness of its direct surroundings which in its turn depends on the illuminance of the space where the screen is located. When the illuminance around the screen varies the maximum illuminance should be considered. The brightness should not be too high; a screen that is too bright will be unpleasant to look at, will be unnecessarily expensive and will negatively influence the surrounding lighting when indoors.

In general:

  • screens located outdoors should have a higher brightness than screens that are placed indoors.
  • Indoor screens that receive direct sunlight need to be brighter, comparable to outdoor screens.
  • When situated directly behind (shopping) windows the reflection of the sun on the window should also be taken into account.
  • TV screens should not be illuminated by (spot) lights to avoid reflections on the screen which reduce readability.

Since brighter screens have a higher purchase price, use more electricity and, depending on the screen technology, need to be replaced more frequently it makes sense to use a screen that has just enough brightness for the specific location where it is used. Some professional screens have a light sensor that is used to adjust the brightness to the illuminance of the environment. This ensures good visibility at lowest energy use and can be a valuable feature for screens that are placed in locations with variable lighting conditions.

A general rule of thumb when it comes to screen brightness;

  • for indoor screens; a brightness of at least 300 nits and double the illuminance - so if the illuminance in a room is 200 lux the brightness of the screen should be 400 nits.
  • for outdoor screens the 2 to 1 rule holds but a maximum of 3000 nits is enough in most situations. The factor 2 can be adjusted down in situations with higher illuminance to 1,5. Since most outdoors situations have an illuminance of 1000 lux a minimum brightness for outdoor screens is around 2000 nits, which rules out consumer TV screens. When outdoor screens are used at night they should not be brighter than 100-150 nits when it is dark1. Keep in mind that many countries have rules and regulations concerning the brightness of outdoor signage at night.

A more detailed advice can be found in the table below.

Does the screen technology matter?

Digital signage screens are available in a number of technologies; LCD, OLED and LED to name a few. There are a number of pros and cons to each of these technologies. Focussing on the brightness of the screen there are a few things that you should take into consideration with regards to these technologies:

  • LED screens have a higher brightness then LCD and OLED screens
  • LCD screens can be damaged by direct sunlight
  • LCD screens suffer more from reflections reducing legibility in situations where the screen is lit (by a spot light)
  • LED screens are more expensive, require specialised installation and use more electricity than LCD and OLED

Special care should be given to situations where screens are placed behind a shopping window. Using a bright screen will probably solve visibility issues but is more expensive to purchase and in use of electricity. Placing the screen close to the glass and making sure the surrounding light is adjusted can eliminate the need for high brightness screens. When screens need to be encased in a protective cabinet be sure to involve professionals with experience in this field.

Overview of typical ambient illuminance and appropriate screen brightness

To support your decision making we include a table of typical ambient illuminance and the recommended screen brightness for environments where digital signage is used. Using this table you will get a more detailed advice than using the "rule of thumb" explained above.

Industry Workspace Typical ambient illuminance
(in lux or lm/m2)
Recommended screen brightness
(in nits or cd/m2)
Aviation and Transportation Airport departure hall 350 – 5,000 700 – 2,500
Departure gates 350 – 2,500 700 – 2,500
Check-in area 300 – 2,000 600 – 2,500
Corporate Office Corridors 50 - 250 350 - 500
Meeting room 150 - 500 350 - 800
Board room 200 – 700 400 – 1,000
Reception area 250 – 1,000 500 – 1,600
Office desk area 200 – 500 350 - 800
Atrium 400 – 5,000 700- 2,500
Digital Cinema Cinema lobby and ticket office 200 – 2,000 400 – 2,500
Cinema window frontage/glazed facade 1,000 – 10,000 1,700 – 2,500
DooH Roofed area 2,000-10,000 2,500
Outdoor area 5,000-50,000 2,500
Education Corridor 100 – 300 350 - 600
Classroom 150 – 500 350 - 800
Auditorium 200 – 1,000 400 – 1,600
Healthcare Reception area 250 – 1,000 500 – 1,600
MDT room 150 - 350 350 - 650
Waiting room 150 – 500 350 - 800
Hospitality Entrance area 300 – 2,000 700 – 2,500
Reception 250 – 1,000 500 – 1,600
Corridors/staircases 100 - 250 350 - 500
Leisure and Museum Sports and event arena 200 – 1,000 400 – 1,600
Museum 200 – 1,000 400 – 1,600
Quick Service Restaurant Restaurant window frontage/glazed facade 1,000 – 10,000 1,700 – 2,500
Menu board 250 - 500 350 - 800
Self-ordering kiosks 250 - 600 500 – 900
Drive-through menu board (Housing) 5,000-50,000 2,500
Rental and Staging Outdoor area 5,000-50,000 2,500
Trade show stand 250 – 2,500 500 – 2,500
Sports and event arena 250 – 1,000 500 – 1,600
Retail and Signage Store frontage/glazed facade 1,000 – 10,000 1,700 – 2,500
Entrance area 300 – 1,000 600 – 1,600
Pharmacy interior 250 – 1000 500 – 1,600
Retail store interior 250 – 700 500 – 1,000
Grocery store/supermarket interior 250 – 600 500 – 900
Product showroom 350 – 1500 600 – 2,500

Source NEC2

References

The following documents were used in writing this article:

  1. Report on digital sign brightness, Jerry Wachtel, 2014
  2. How Display brightness affects successful implementation of Digital Signage applications, NEC Display Solutions, 2015