Digital signage in the shop window: how bright does the display have to be?

A screen in the shop window does not compete with other screens, but with the sun. What looks brilliant in the shop is often a dark pane outside at eleven in the morning. In consultations clients ask us first about size, the more important number is brightness.

How bright does a window display have to be?

Brightness is given in candela per square metre, in retail usually as nits. A living room television delivers 250 to 400 cd/m², a signage display for interiors 500 to 700. Behind glass with daylight from the side you need at least 1,500 cd/m²; with direct sun on the pane 2,500 to 4,000. Anyone who wants to know precisely measures the illuminance on site with a lux meter: an overcast day brings around 10,000 lux onto the pane, full summer sun over 50,000. For the first value a device with 2,500 cd/m² is quite enough; for the second only a high-brightness display or an LED surface comes into question.

Reflections: the underestimated problem

Even a bright display loses against the reflection of the street if the eye focuses on the pane instead of the picture. Three measures help: an anti-reflective front glass on the device, a slight tilt of three to five degrees downwards and a dark, calm background in the window. Light decoration behind the screen makes it look flatter, not brighter.

Heat behind glass

Professional window displays are rated up to 50 °C ambient temperature and throttle themselves in heat. A television from the electronics store is specified up to about 35 °C. Keep at least ten centimetres from the pane, leave air above and below and avoid closed cladding. The black patches we often see after the first summer are heat damage, and no warranty covers them.

Power consumption and operating hours

A 55-inch high-brightness display draws 250 to 400 watts at full power, an indoor device about half. At 14 hours a day that comes to 1,500 to 2,000 kilowatt-hours a year. Two levers lower the figure: an ambient light sensor that adapts brightness to daylight, and a timer that switches the device off at night or dims it to 20 per cent. Both also extend the panel's life. Many municipalities, Solothurn and Bern too, regulate in their sign regulations when illuminated advertising has to be switched off; moving images by the road usually require a permit. Ask before installation.

Window film or display?

We see it every day: anyone who wants to address passers-by in daytime cannot get past the display. Anyone who wants to play the evening hours does well with film.

Conclusion

Brightness from 2,500 cd/m², air around the device, light sensor and timer: with that a window display works for years. We measure the light conditions on site and show how different brightness classes perform in daylight.

More on this: digital signage and vehicle and shop lettering.