ANIMA | The halo effect in out of home advertising

For years, out of home advertising has been judged by a single question: how many people walked past our advertising site? It is a necessary question, but an incomplete one. An OOH or DOOH campaign does not end at the billboard or the screen. It carries on in the brand search someone makes on their phone a few minutes later, in a direct visit to the website, in a digital ad that suddenly performs better than it would without prior outdoor exposure, or in the store that person decides to walk into.

This knock-on effect on the rest of the channels is what we call the halo effect, and it is probably the most underrated value of out of home advertising within media planning.

Below, we look at what it is, where it shows up, how it can be measured and what it means for those planning omnichannel campaigns.

What Is the Halo Effect in Out of Home Advertising?

The OOH halo effect is the indirect impact that an out of home campaign has on other channels and metrics: more brand searches, more direct traffic, better performance from digital campaigns or more store visits, without those channels having received any additional investment.

In other words, it does not measure what the site achieves on its own (a QR code scan, for example), but what it triggers around it. And that is the key: OOH rarely closes the sale on its own, but it often paves the way for other channels to do so.

A clarification to avoid confusion: this halo effect is not the same as HALO, the cross-media reach and frequency measurement framework promoted by the WFA.

Where the OOH Halo Shows Up

The halo effect does not appear in a single place. It shows up at several points of the consumer journey, across different advertising channels:

• Brand search: more searches for the brand or product name in search engines.
• Direct traffic: more visits to the website or app without the consumer having first gone through an online ad.
• Digital performance: higher CTR and response rates in display, social and paid search.
• Store visits: more footfall in stores close to the exposed areas.
• Brand recall and conversation: more awareness and more presence on social media.

To see how this plays out in practice, take the case published by AdQuick on a Rover campaign in San Antonio (US), which compared areas with OOH advertising against control areas without it. In the exposed areas, the click-through rate of mobile display advertising was 26.15% higher, and paid search response rose by 166% during the campaign, compared with 42% in areas without OOH.

Of course, this is a single case, and results vary by sector, market and methodology, but it illustrates the logic well: digital channels respond better where out of home advertising has made an impact first.

(If you want to explore how the street feeds the digital conversation, don’t miss: From OOH to Online: How Out of Home Advertising Fuels Digital Conversation)

Why OOH Generates Halo: Reach, Context and Timing

There are three main reasons why out of home advertising is such an effective trigger of the halo effect.

• Reach: according to a Kantar study of more than 600 European campaigns, reported by LBB, OOH is the channel with the second highest reach, behind only television.
• Receptivity: in its Media Reactions 2025 report, Kantar ranked OOH and DOOH second and third among the channels where consumers are most open to receiving advertising, precisely because it is not intrusive.
• Context: the OOH audience is on the move, on the street, on public transport or on the way to a store, and almost always with a phone in hand. It is the ideal setting for an exposure to turn, minutes later, into a search, a scan or a visit.

This mechanism also helps explain another finding from the same source: campaigns that combine five or more channels can deliver up to three times the impact, with the halo effect being the way those channels amplify one another.

How to Measure the Halo Effect: From Impressions to Incrementality

Knowing how many people walked past a site does not, on its own, tell you whether that exposure led to a visit or a purchase. To measure the halo, you need to move from measuring audience alone to measuring incrementality: what has changed, and improved, because of the campaign compared with what would have happened without it. These are the most commonly used approaches for accurate measurement:

1. Geo Tests with a Control Group: this approach simply compares areas with the brand’s OOH advertising against similar areas without it, and then analyses the difference in direct brand searches, web and app traffic, store traffic or sales, among other metrics. It is the most robust way to isolate the causal effect of the campaign.
2. Brand Lift and Search Lift Studies: these studies measure the change in brand recall, consideration and brand search volume between exposed and non-exposed people. They are particularly useful for understanding the impact at the top of the funnel.
3. Geofencing and Mobile ID Matching: these measurement techniques make it possible to identify the devices that have been near a site and observe their later behaviour, such as a store visit or a digital interaction. They rely on the same technological foundation behind hybrid experiences between the digital and the physical. (If you want to see how screens and mobile phones connect, take a look at: The Future of Out of Home Advertising: Hybrid Experiences Between the Digital and the Physical)
4. Marketing Mix Models: these models estimate each channel’s contribution to final results, and they become far more reliable when calibrated with the results of geo tests.

That said, there is one important caveat: without a control group, an increase in searches may be due to seasonality, a promotion or a simultaneous campaign in another medium. That is why halo measurement must be designed before the campaign launches, never after. Otherwise, it is easy to make avoidable mistakes that undermine all of the campaign’s comparative results, producing biased data and steering our strategy in the wrong direction.

The industry is also moving towards increasingly consistent measurement frameworks, as we explore in DOOH in 2026: Challenges, Advances and a New Standard in Digital Out of Home, which makes it easier to compare results across channels and markets.

What This Means for Media Planning

Measuring the halo effect is not just a matter of post-campaign analysis: it has to start at the planning stage. If the plan is not designed in advance to capture and measure what OOH triggers in other channels, that impact will be lost or attributed to another medium. These are some practical guidelines worth applying from the very start of the campaign to avoid measurement errors:

• Define halo KPIs from the briefing: decide before launch which indirect effect will be measured (brand searches, direct traffic, visits…) and over what period.
• Synchronise flights: keep search and social campaigns active in the areas where the OOH advertising runs, so you can capture the demand this channel generates. If those channels are switched off, the halo has nowhere to convert and loses its purpose.
• Design control areas: set aside similar areas without OOH advertising to compare against the areas that do have it. Without comparison there is no incrementality, and the measurement would therefore produce no conclusive results.
• Don’t evaluate OOH by last click: this model attributes the conversion to the last channel the user interacted with, usually a search or a digital ad. OOH rarely occupies that position, but it is often what led the person to search for the brand. Measuring it this way leaves out precisely the effect it generates.

Ignoring the halo leads us to undervalue out of home and, with it, to cut budget where the multiplier effect is greatest. (To understand what can happen when out of home advertising disappears from the mix, don’t miss: What Happens If You Remove Outdoor Advertising from Your Media Plan?)

The Halo: The Argument Missing from the OOH Conversation

Out of home advertising does not need to compete with the rest of the channels, but to prove what it does for them. The halo effect makes it possible to justify investment in OOH and DOOH with data, and to approach media planning as a system in which each channel strengthens the next.

For agencies planning campaigns across several markets, measuring this effect from the start is a competitive advantage, as it turns an industry intuition into a solid argument for the client.

Do you want to measure the real impact of out of home advertising on your clients’ campaigns? We can help you plan OOH and DOOH with measurement criteria built in from the briefing. Shall we talk?