LED and digital outdoor media: what actually matters when you buy it

Digital out-of-home is sold on numbers, and the numbers are easy to present flatteringly. A screen advertised as reaching two hundred thousand people a day may be showing your creative for six seconds in a ninety-second loop, which is a very different proposition. Knowing which figures to interrogate is most of the skill in buying DOOH well.

Slot duration and loop length

These two numbers together decide your actual share of the screen. A ten-second slot in a sixty-second loop means your creative is on screen one sixth of the time — roughly ten minutes in every hour of operation. The same ten-second slot in a one-hundred-and-eighty-second loop is a third of that.

Share of voice is slot duration divided by loop length. Ask for both numbers, never just one.

Loop length also tends to grow over a site's life as more advertisers are added. A site that quoted a sixty-second loop when it opened may be running one hundred and twenty seconds a year later, halving what every existing advertiser gets without anyone renegotiating.

Operating hours

An impression count is meaningless without the hours behind it. A screen running from six in the morning to eleven at night gives seventeen hours of plays; one that switches off at eight in the evening gives fourteen, and loses the entire evening commute. When comparing two sites, normalise to plays per day rather than trusting the headline reach.

Pixel pitch and viewing distance

Pixel pitch is the distance in millimetres between adjacent LEDs. Smaller pitch means finer detail and a higher price. The important point is that pitch only matters relative to how far away the viewer is: a P10 screen looks coarse from three metres and perfectly sharp from thirty. Paying for a P4 panel on a highway is paying for detail nobody is close enough to resolve.

• Indoor, close viewing (malls, lifts, retail): finer pitch earns its cost.
• Roadside at distance: a coarser pitch is usually the honest choice.
• Ask for screen resolution in pixels, not only the physical size — that is what your creative must be authored to.

Brightness and legibility

Brightness is measured in nits. A screen bright enough indoors will wash out completely in direct afternoon sun, and a screen bright enough for daylight will be uncomfortably glaring at night unless it dims automatically. Automatic brightness adjustment is worth asking about specifically — without it, a site is either unreadable for part of the day or a nuisance for the rest of it.

What to ask for in writing

• Slot duration, loop length, and whether loop length is capped.
• Operating hours, and estimated plays per day derived from them.
• Screen resolution in pixels and accepted creative formats.
• Whether the site shares the loop with public-service or operator content.
• Uptime history, and what happens to your slots if the screen fails.

That last point is the one most often left vague. A digital site that goes dark for a week has not delivered what a static hoarding would have delivered in the same week, and the contract should say what follows from that.