Window-Facing Digital Signage Buyer's Guide: Why an Ordinary Screen Fails Behind Glass

Short answer: A window-facing display is an indoor screen that has to win against the outdoor sun. It sits behind the shop glass, so it does not need to be waterproof — but it does need three things an ordinary commercial screen does not have: enough brightness to stay readable against daylight coming from behind the viewer, a way to get rid of the heat that builds up in a sunlit window, and content that can be read by someone walking past on the pavement. Below are the seven points to check, in order, and the questions to put to any vendor.

1. Brightness: match it to how much sun the window gets

A standard indoor commercial display is rated around 350–500 cd/m² (nits). Outdoors, a bright overcast day is already several thousand lux at the glass, and direct sun is far more. Against that background, a 500-nit screen looks grey and switched off.

The practical ranges for window use:

North-facing or permanently shaded window, or a window under a deep awning: 1,500 cd/m² is usually enough.
Window that gets partial or afternoon sun: 3,000 cd/m².
South- or west-facing window in direct sun for hours: 4,000 cd/m².

Two things to remember. First, the number on the spec sheet is the panel's peak; ask whether it is measured on the finished unit. Second, more is not always better: a 4,000-nit screen in a north-facing window costs more to buy and to run than it needs to.

Ask the vendor: "What is the rated brightness of the complete unit, and which of your models would you recommend for a window facing [your direction]?"

2. Auto-dimming: the feature that matters after sunset

A screen bright enough for midday is far too bright at night. Left at full brightness, a window display becomes a glare source for pedestrians and drivers, draws complaints from neighbours in mixed-use streets, and wears out its backlight faster than it should. An ambient-light sensor that lowers the brightness automatically as the street gets darker — and brings it back up in the morning — solves all three.

Not every brightness class includes this. Check whether the sensor is standard on the model you are considering rather than an option.

Ask the vendor: "Does this model have an ambient-light sensor with automatic dimming as standard?"

3. Heat: the problem nobody sees until summer

This is where window displays differ most from other indoor screens, and where most failures come from.

A shop window is a greenhouse. Sunlight comes through the glass, hits the back of the display, and the heat cannot escape the way it would outdoors. On top of that, a high-brightness backlight generates far more heat than a normal screen. The result is a display working in a hot, enclosed pocket for several hours every sunny day.

Vendors deal with this in one of two ways:

Fans and vents. Cheaper to build, but fans pull dust from the shop floor through the unit, filters clog, and a fan that stops in July takes the panel with it. Fans are also audible in a quiet shop.
Fanless, sealed construction. No moving parts and no filters; the housing itself is engineered to conduct heat away from the panel and electronics. Silent, nothing to clean, nothing to fail mechanically — but it only works if the thermal design was done properly at the factory, so it is worth asking how it is done rather than just whether it is done.

Ask the vendor: "Is the unit fanless? If not, what is the filter-cleaning interval and who does it? If it is, how is heat removed from the panel?"

4. Single- or double-sided: one unit, two audiences

A window display usually faces the street. A double-sided unit adds a second screen facing into the shop, so the same hanging position serves passers-by and customers inside at once — useful for menus, promotions, or listings that both audiences need. Double-sided units are typically hung from the ceiling in the window bay, so the two faces are unobstructed.

Decide this before you choose a size, because a double-sided unit is heavier and needs a ceiling fixing that can take the load.

Ask the vendor: "Is the double-sided version available in the size I need, and what is its weight with mounting hardware?"

5. Size, mounting and distance to the glass

Window displays come in a range of sizes — 43" for a small shopfront, 55" and 65" for a typical retail window, 75" and 86" where the window is large or the viewing distance is longer. The two mounting options are ceiling-hung (the display hangs on cables or rods inside the window, common for double-sided units) and floor-standing (a base or stand placed just behind the glass).

Three practical points:

Keep the screen close to the glass. Every centimetre of gap adds reflection from the window itself and lets more ambient light wash across the screen. But leave enough room for the unit to breathe and for cleaning.
Check the ceiling. A large ceiling-hung display needs a fixing rated for its weight, and the cable route to power and data has to be planned before the shopfitter leaves.
Portrait or landscape? Most windows are taller than they are wide; portrait is the natural choice and gives larger text at eye level.

Ask the vendor: "What mounting options are available for this size, and can you provide the mounting drawing and weight?"

6. Readability from the pavement

The viewer is outside, walking, and looking through a sheet of glass. Design for that: large text (a passer-by at 2–3 m needs roughly 12 mm or more of text height on a 55" screen), high contrast, few words per screen, and content that changes slowly enough to read. Avoid dark backgrounds with small light text — reflections of the street will land exactly where the text is.

Reflections from the window glass itself are a separate issue from the display and depend on the glass, the angle of the sun and what is across the street; a slight tilt of the display or an awning often does more than any screen feature.

7. What it costs in years two and three

The purchase price is the smaller number. From the second year, a window display costs you power (a high-brightness backlight running twelve hours a day is not trivial — auto-dimming pays for itself here), content management, and maintenance. On fan-cooled units, that means filter cleaning and eventually fan replacement; on any unit, it means whether the power supply and media player can be replaced without taking the whole display out of the window. Ask these questions now, while the vendors are still competing for the order.

Ask the vendor: "What is the power consumption at full and at dimmed brightness? Can the power supply and media player be replaced on site?"

Checklist (paste into your RFQ)

Window orientation and hours of direct sun: ______
Rated brightness of complete unit: ______ cd/m² (1,500 / 3,000 / 4,000)
Ambient-light auto-dimming: standard · optional · none
Cooling: fanless sealed / fan + filter (interval: ______)
Single-sided / double-sided
Size: 43 / 55 / 65 / 75 / 86" · portrait / landscape
Mounting: ceiling-hung / floor-standing · weight: ______ · drawing: yes / no
Power consumption (full / dimmed): ______
PSU / media player replaceable on site: yes / no

How EKAA's window-facing displays answer these points

For reference, EKAA's window-facing series answers the checklist as follows: fanless construction across the whole range, with no fans or filters to maintain; brightness options of 1,500, 3,000 and 4,000 cd/m², with an ambient-light sensor and automatic dimming standard on the 3,000 and 4,000 cd/m² models; single- and double-sided versions; 43", 55", 65", 75" and 86" sizes; and ceiling-hung or floor-standing mounting.