How bright should a digital signage screen be?

When setting up digital signage, screen size is important, but screen brightness plays an even bigger role in visibility, costs, and energy efficiency. This guide explains what brightness means, how it relates to ambient light, and how to select the right brightness for different digital signage environments.

What is screen brightness in digital signage?

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).

Why screen brightness matters for digital signage

• Visibility: content stays readable in different lighting conditions.

• Costs: higher brightness = higher purchase price + energy use.

• Durability: some technologies (LCD) are more prone to sunlight damage.

• Compliance: many regions regulate outdoor screen brightness at night.

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.

Brightness by screen technology

• LED screens: highest brightness, ideal for outdoors, but higher cost + power use.

• LCD screens: affordable, but weaker in sunlight and prone to reflections.

• OLED screens: good contrast, but not suitable for high-brightness environments.

👉 For shop windows: combine positioning + lighting adjustments to reduce the need for ultra-bright screens.

Recommended screen brightness levels for digital signage

References

• Report on digital sign brightness, Jerry Wachtel, 2014

• How Display brightness affects successful implementation of Digital Signage applications, NEC Display Solutions, 2015