When you plan to use digital signage and are wondering what screens to use, there are several aspects that you should consider. The most obvious one is the size of the screen.
The subject of a previous blog post is how to choose the best screen size. However, a second factor you should consider is the screen's brightness, which can significantly influence the screen's price and running costs. This article will explain what brightness is and what things you should consider in choosing a screen and includes a table of what screen brightness to best use in typical digital signage environments.
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 luminance) 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 emitted from all light sources in a room/location - lamps and/or the sun - 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, brightness is the measure of light coming from a screen, and illuminance is the measure of light in a space. So, it makes sense that for content on a screen to be visible, it has to be brighter than the objects around it (which are illuminated by the ambient light).
What determines the proper brightness
The "correct" brightness of a screen 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 screen's location. When the illuminance around the screen varies, the maximum illuminance is considered. On the other hand, the brightness should not be too high; a screen that is too bright will be unpleasant to look at, unnecessarily expensive, and negatively influence the surrounding lighting indoors.
In general:
- Screens outdoors should have a higher brightness than screens placed indoors.
- Indoor screens that receive direct sunlight need to be brighter than outdoor screens.
- When situated directly behind (shopping) windows, account for the sun's reflection on the window.
- Do not illuminate TV screens 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 with just enough brightness for its location. In addition, some professional screens have a light sensor allowing them to adjust the brightness to the illuminance of the environment. Adaptive brightness ensures good visibility at the lowest energy use and can be valuable for screens 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.
- The 2-to-1 rule holds for outdoor screens, but a maximum of 3000 nits is enough in most situations. Factor 2 can be adjusted down in cases with higher illuminance to 1,5. Since most outdoor conditions have an illuminance of 1000 lux a minimum brightness for outdoor screens is around 2000 nits, which rules out consumer TV screens. When using outdoor screens at night, they should not be brighter than 100-150 nits1. Keep in mind that many countries have rules and regulations concerning the brightness of outdoor signage at night.
The table below contains more detailed advice on the screen brightness.
Does the screen technology matter?
Digital signage screens are available in several technologies; LCD, OLED and LED to name a few. There are some pros and cons to each of these technologies. Concerning screen brightness, there are a few things that you should take into consideration concerning these technologies:
- LED screens have a higher brightness than LCD and OLED screens
- Direct sunlight can damage LCD screens
- LCD screens suffer more from reflections reducing legibility in situations where the screen is lit (by a spotlight)
- LED screens are more expensive, require specialized installation, and use more electricity than LCD and OLED
Placing a screen behind a shopping window takes special care. A bright screen will probably solve visibility issues, but it is more expensive to purchase and use electricity. Placing the screen close to the glass and ensuring the surrounding light is adjusted can eliminate the need for high-brightness screens. When screens need to be protected, involve professionals with experience in encasing screens.
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 that environment. Using this table, you will get more detailed advice than 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:
- Report on digital sign brightness, Jerry Wachtel, 2014
- How Display brightness affects successful implementation of Digital Signage applications, NEC Display Solutions, 2015