How bright a touchscreen foyer display needs to be

How many nits does a foyer screen need?

For a foyer, buy on where the light lands: 400 to 500 nits is enough on a wall the sun never touches, 700 to 1,000 nits when a sun patch crosses the screen part of the day, 2,500 nits for a screen facing the window.

A nit is one candela per square metre, so a specification sheet quoting cd/m² is quoting the same figure in different clothes. The classes below are trade practice, not a rule: they are where indoor touch panels are actually built and where installers land when a picture has to survive the light in the room.

Most indoor touch panels ship in the 400 to 500 nit class, which is why a screen bought off a standard specification sheet washes out the moment a beam crosses it. The class you need is set by the worst hour of light at your wall, and the next sections show how to measure that hour and turn it into a nits figure.

What does daylight do to a screen picture?

Daylight does not damage the picture, it buries it: every lit surface in front of the glass adds a layer of glare on top of the image, and the panel only stays readable while its own brightness stays well above that glare.

The light ladder is easy to confirm with a lux meter. Ordinary office and shop lighting sits at 300 to 500 lux. Daylight through glass without a direct beam lands a few thousand lux on a nearby wall. Direct sun measures about 100,000 lux at full strength, and a beam through entrance glass still carries tens of thousands into the room.

Glass is what turns that light into glare. Each air-to-glass surface reflects roughly 4 percent of the light hitting it, so an uncoated front on a touch display is planned at about 5 percent. The glare sitting on top of the picture is then one line of arithmetic:

glare in nits ≈ lux at the screen face × 0.05 ÷ 3.14

The division by 3.14 converts reflected lux into reflected nits for a diffuse surface, and nits are the same unit as candela per square metre, so the result compares straight against the panel rating. The planning floor that follows: keep the panel at or above the glare luminance, which is a 2:1 on-screen ratio and about the lowest point where large text still reads, while small text wants 3:1 or better, the same floor accessibility guidance uses for on-screen text. Diffuse daylight rarely threatens that floor. A bright 2,500 lux window wall adds about 40 nits of glare, and a 400 nit panel still sits above 10:1. The direct beam is the killer, and the worked example below puts numbers on it.

How do you measure the light at your wall?

Measure the light at the screen face, not at the window: take a light meter reading where the panel will sit at the worst hour of the day, because the sunlit patch reads in the tens of thousands of lux and the wall beside it in the hundreds.

A phone light meter app is accurate enough to choose between classes, and a stand-alone lux meter costs little and removes doubt. Take a reading every 30 minutes across the opening hours for one day, at the height and position where the screen face will sit, angled the way the panel will face. Write down the highest reading of the day and the reading at your busiest hour.

The season matters more than the day. A low winter sun shines straight through entrance glass and throws its beam deep into a foyer, while a high summer sun through high glass can miss the wall entirely. If you can only measure once, measure when the sun is low and the beam reaches deepest into the room, and size the panel to that worst reading, not to the day's average.

Worked example: how many nits for a screen 12 ft from the door?

A 55 inch touch panel on a foyer wall 12 ft from the standing spot, with direct sun crossing it for about 90 minutes mid morning, needs about 1,000 nits to stay readable through the patch, and a 400 nit panel drops to roughly 1.5:1 contrast there.

The wall carries a 55 inch class touch panel mounted 12 ft from where people stop and read, with a glass entrance across the foyer. For about 90 minutes mid morning the direct beam crosses the screen and the meter reads 50,000 lux on the screen face. The rest of the day the same spot reads 400 lux.

Step 1, glare in the patch. 50,000 lux × 0.05 ÷ 3.14 ≈ 800 nits of reflected light sitting on top of the picture.

Step 2, contrast through the patch. A 400 nit panel gives (400 + 800) ÷ 800 = 1.5:1, which the eye reads as a grey wash. A 1,000 nit panel gives (1,000 + 800) ÷ 800 = 2.25:1, enough for headlines and slide titles to carry. That gap between 1.5 and 2.25 is the whole argument for the daylight class.

Step 3, text size at that distance. The FHWA planning figure is 30 ft of viewing distance per inch of capital letter height, so 12 ft calls for 0.4 in capitals. The safer choice for fast reading in high traffic is 20 ft per inch, 0.6 in capitals. The small screen text readability article carries that arithmetic further.

Step 4, the decision. Buy 1,000 nits, or remove the patch. Blinds, or sliding the screen 6 ft along the wall until the beam misses, drop the face back into the 400 lux reading, where the same arithmetic gives 400 × 0.05 ÷ 3.14 ≈ 6 nits of glare and a contrast near 70:1. A standard 400 to 500 nit touch display then does the job.

One limit of the formula: it models diffuse bounce only. A glossy front that mirrors the bright window adds a specular image the line above never sees, which is why the daylight class begins at 700 nits instead of at the formula's bare minimum.

Does touch glass change the brightness you need?

Touch glass sits in front of the LCD and trades away a little brightness while adding one more reflective surface, so the number to ask for is the brightness of the finished touch display, not the bare panel behind it.

Three practical points follow. Ask whether the quoted nits figure was measured through the touch glass or on the bare panel before assembly, because the glass takes its share. Ask whether the figure is typical brightness across the full screen or a peak measured on a small window of the panel, because peak figures flatter. And note that touch shifts the margin slightly, it does not move a screen between classes, so the same light table applies to a touch wall and a non-touch wall alike.

When is a brighter panel the wrong answer?

If the sun patch crosses the screen for an hour or two a day, moving the screen or shading it beats paying for brightness, because a screen moved 6 ft out of the patch sees daylight a class lower and a standard 400 to 500 nit panel reads fine.

• Move it. Sliding the screen along the wall until the patch misses, even 3 to 6 ft, drops the light at the face by a whole class, and the worked example above shows what that does to the arithmetic.

• Shade it. Blinds, a hood, or a recess built into millwork cut the beam off entirely. If the screen is going into a wall or a joinery panel, the flush mount and cut-out guide gives the real cut-out sizes before the carpenter cuts.

• Automate it. An ambient light sensor lets the panel climb through the sun patch and settle back down for the evening, and the sun sensor versus brightness sensor selection and mounting guide covers which sensor type suits a foyer and where it mounts.

• Dim at night. The evening half of that swing has its own article on dimming a screen below its lowest night setting.

Heat is the second reason to fix the light before paying for brightness. Full sun carries about 1,000 W per square metre, and a dark glass front inside a beam runs well above room temperature, so check a panel's stated operating temperature range before fixing one where the beam lands. The article on sun protection for a display cover in direct sun covers what years of that exposure do to a front.

What should you ask the supplier for?

Ask for four things in writing: the panel brightness in nits, whether that figure is measured through the touch glass, the operating temperature range if the wall takes sun, and whether the panel takes an ambient light sensor to raise and lower brightness through the day.

Two of the four need a sentence each. The temperature range matters because a foyer wall that takes a beam runs hot, as the heat note above shows, and a panel with a narrow range misbehaves there long before brightness becomes the question. Connectivity matters if you bring your own player: an external player drives the picture over HDMI and reads touch back over a separate USB cable, while an all-in-one touch panel runs the content itself with no return cable. Get the nits figure and its measurement condition in writing before you order, and the rest of the list is a single number or a yes.

Which screen should you actually buy?

Buy the 700 to 1,000 nit class for a foyer screen that takes a sun patch, keep the standard 400 to 500 nit class for a shaded wall, and if the screen faces the window all day, buy the 2,500 to 3,000 nit window class or move the screen.

Recommendation: Take a lux reading at the screen face at the worst hour. Under 1,000 lux, order the standard 400 to 500 nit touch class. A measured sun patch on the glass, order the 1,000 nit daylight class, or move and shade the screen until the patch is gone and stay standard. A screen that faces the glass for most of the day needs the 2,500 to 3,000 nit window class or a new position.

Our own lobby screens are the small panel-mount series, 10.1 to 23.8 inches, portrait or landscape, with capacitive or resistive touch and playback from microSD or USB with no subscription, right for a counter sign or a door-side board read from a few feet. A 55 inch foyer wall sits outside that series: the current display range runs through 75 inches and is quoted per project, so write the nits figure, the touch type and the measurement condition into the quote. The lobby display category shows what the small series is built for.

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