1. What a nit actually measures
A nit is not an SI unit. It is the accepted name for one candela per square metre, so 1 nit equals 1 cd/m². Some spec sheets use both on the same page, which reads as if two different properties were being described. It is one property with two names.
Luminance is light leaving a surface in a given direction. It is not illuminance, which is light arriving at a surface and is measured in lux. The distinction is worth holding on to in an RFQ: a supplier quoting a lux figure for a display is quoting the wrong quantity.
Luminance is also directional by definition. A figure quoted on axis is the best case an LCD will produce, and the fall-off away from that axis is a separate specification. Read brightness and viewing angle together, not separately.
The spread across one product range shows how much the application drives the number. Our wall-mount signage line runs 300 to 500 cd/m². The high-brightness window line runs 700 to 5000 nits. The outdoor IP66 line runs 1500 to 5000 nits across 32 to 86 inch. Same unit, three different jobs.
2. Peak against sustained: the number that gets quoted
Peak brightness is measured on a small bright window against a mostly dark screen. Sustained brightness is what the panel holds across a full white field. On a locally dimmed panel the gap between the two is large, because the backlight can concentrate output where a test pattern needs it and cannot do that for a full screen of white.
The Mini LED line is quoted at up to 2000 nits peak with local dimming and 1,000,000:1 contrast. Peak is the right figure for comparing one Mini LED panel against another and the wrong figure for comparing it against a full-array panel quoted on a full white field. Mixing the two is the most common way two quotes end up not being comparable.
Ask three things. Is it peak or sustained? What window size was used for the peak measurement? Is the number typical or minimum? Only a minimum value is enforceable in a purchase contract, and a typical value is usually several percent above it.
Brightness is not free either. On the portable battery line, a 43 inch unit rated 1500 to 2000 nits runs 12 to 14 hours at typical brightness and 8 to 10 hours at maximum output. Roughly a third of the runtime is spent buying the top of the brightness range. On mains-powered units the same trade arrives as heat and fan noise instead of as lost battery hours.
3. Where in the stack the number is measured
The same panel measures differently at three points: at the open cell, behind the cover glass, and at the front of the finished housing. Every interface the light crosses reflects part of it back and transmits slightly less than what arrived.
A bare air-to-glass interface reflects about 4 percent at normal incidence. That is the Fresnel reflection for glass at a refractive index of 1.5, and it applies at each interface in the stack. An air gap between the cover glass and the panel adds two more.
So a figure measured at the open cell is not the figure a viewer sees. Ask which point the quoted number refers to, and ask whether the cover glass and any bonding are included in it. A supplier who cannot say which point the number came from has not specified the product, only the panel inside it.
4. Why reflection decides readability in daylight
Daylight readability is a contrast problem, not a brightness problem. Reflected sunlight adds the same amount to the white parts of the image and to the black parts, so it compresses contrast from both ends at once. Raising the backlight only pushes up one end.
Reflected luminance from a diffuse surface follows R = ρE/π, where ρ is the surface reflectance and E is the illuminance in lux. Take a hard case: 20,000 lux falling on the glass, a panel with 1000:1 native contrast, and compare an air-gap stack at 4 percent reflectance against a bonded stack with anti-reflective treatment at 1 percent.
- 700 nits at 4 percent reflection: ambient contrast drops to 3.7:1.
- 1000 nits at 4 percent reflection: 4.9:1.
- 1500 nits at 4 percent reflection: 6.9:1.
- 2500 nits at 4 percent reflection: 10.7:1.
- 700 nits at 1 percent reflection: 11.9:1.
- 1000 nits at 1 percent reflection: 16.4:1.
- 1500 nits at 1 percent reflection: 24.0:1.
- 2500 nits at 1 percent reflection: 38.7:1.
Read that in one direction first. Going from 1000 to 2500 nits on an air-gap stack improves ambient contrast by about 2.2 times. Cutting reflection from 4 percent to 1 percent on the same panel improves it by about 3.4 times. The reflection fix costs less than the backlight, draws less power, and runs cooler. A 700 nit bonded screen at 11.9:1 beats a 1500 nit air-gap screen at 6.9:1, and costs less to run for the same result.
That is why optical bonding sits on the sunlight-readable lines rather than in the options column to be trimmed at value engineering. It removes the internal air gap and the two reflections that come with it. The figures above are a model with stated assumptions, not a test report, so use them to rank options against each other rather than as absolute readings. Only the diffuse component is counted; specular glare is additional and depends on the geometry of the site.
5. Brightness tiers by site
Match the tier to the light the screen actually has to fight, not to the light it might see on the best day of the year. These tiers come from our own shipped ranges, so each one has a product behind it rather than a rule of thumb.
- 300 to 500 cd/m² covers indoor retail walls, lobbies, meeting rooms and transport concourses. This is the wall-mount signage range, built for continuous duty on industrial grade panels with 30,000+ hour backlight life.
- 400 to 700 cd/m² covers shelf edges and bar format screens in lit retail aisles. See the LCD bar display line.
- 700 to 1500 nits covers storefront glass that faces the street but not direct sun, and semi-outdoor positions under an awning.
- 1500 to 2500 nits covers direct sun for part of the day. This is the entry point for the outdoor IP66 line, which holds that output across an operating range of -20°C to 50°C with smart thermal control.
- 2500 to 5000 nits covers a west or south facing window and any screen in direct sun for most of the day. Pair it with automatic dimming, because a 5000 nit panel is unpleasant to walk past after dark and wastes power all night.
On the window line the cut is handled for you: an ambient light sensor tracks the surroundings and pulls output down to a 200 to 500 nit equivalent at night. If you are specifying for a shopfront rather than an open site, the scene-specific tradeoffs are set out in the high-brightness window display buying guide.
6. What the brightness number does not cover
Four failure modes survive a high nit rating, and all four are cheaper to catch on paper than on site.
Viewing angle. Luminance is quoted on axis. A panel that meets spec straight on can fall well short of it at the angles people actually stand at, and the fall-off is worse on some LCD modes than others. Ask for the luminance at the angle you care about, not just the contrast at that angle.
Polarized sunglasses. An LCD emits polarized light, so a viewer wearing polarized sunglasses can see the screen go dark at certain head angles. It is a frequent complaint on street-facing and outdoor units and it has nothing to do with the nit rating. Walk past a demo unit wearing a pair before you sign anything off.
Uniformity. A brightness figure is normally a centre point or an average across the panel. Large direct-lit panels vary from centre to edge, and a screen that reads well in the middle can look patchy on a full white background. Ask for a uniformity figure and the number of measurement points behind it.
Heat and decay. Backlight output and junction temperature interact, so a panel that hits its rated nits at 25°C may not hold them at the top of the stated operating range. Backlight output also falls over the life of the unit. Ask whether the rated brightness is held at the top of the temperature range, and whether the warranty covers a minimum brightness at the end of the term rather than only at delivery.
7. What to put in the RFQ
Send these eight and you will get quotes you can set side by side.
- Peak or sustained. State which one you are specifying, and the window size used for any peak figure.
- Measurement point. Open cell, behind the cover glass, or at the front of the housing.
- Typical or minimum. A minimum value is the only one you can hold a supplier to.
- Site illuminance. Measure it at the screen position at the worst hour of the day with a lux meter and send the number, not a description of the site.
- Front surface treatment. Anti-reflective coating, optical bonding, or both, and the resulting reflectance figure.
- Dimming range and sensor. The target night level and whether the sensor response is adjustable on site.
- Thermal condition. Confirm the rated brightness is held at the top of the stated operating temperature range.
- Uniformity and warranty. Ask for the measurement basis, and for a minimum brightness at the end of the warranty term.
For a storefront behind glass the constraints shift again, because reflection and mounting depth move to the front of the list and the ingress rating drops off it. The high-brightness window display line is built for that case, and the outdoor IP66 line covers the fully exposed one.
Brightness tiers by site
| Tier | Typical site | Light to beat | Dimming | TZD line |
| 300 to 500 cd/m² | Retail walls, lobbies, meeting rooms, transport concourses | Indoor lighting | Not required | Wall-mount signage |
| 400 to 700 cd/m² | Shelf edges, bar format in lit aisles | Bright indoor retail | Not required | LCD bar display |
| 700 to 1500 nits | Street-facing glass, semi-outdoor under an awning | Indirect daylight | Recommended | High-brightness window display |
| 1500 to 2500 nits | Direct sun for part of the day | Partial direct sun | Required | Outdoor IP66, portable battery |
| 2500 to 5000 nits | West or south facing glass, full-day direct sun | Full direct sun | Required | Outdoor IP66, high-brightness window display |
Frequently Asked Questions
Is a nit the same as cd/m²?
Yes. 1 nit equals 1 cd/m². Nit is the non-SI name for candela per square metre, and both describe luminance, which is light leaving a surface in a given direction. Spec sheets sometimes list both to make one property look like two.
What is the difference between peak and sustained brightness?
Peak is measured on a small bright window against a mostly dark screen. Sustained is what the panel holds across a full white field. On a locally dimmed panel the gap is large, so a peak figure is only comparable to another peak figure measured on the same window size. Always ask which one is being quoted.
How many nits do I need for a shop window?
It depends on whether the glass takes direct sun. Allow 700 to 1500 nits for street-facing glass with no direct sun, and 2500 to 5000 nits for a west or south facing window in direct sun for most of the day. Measure illuminance at the screen position at the worst hour rather than estimating.
Does a higher nit rating always mean better sunlight readability?
No. Reflected light compresses contrast at both ends of the image, so reflection often matters more than output. On a worked model at 20,000 lux, taking a panel from 1000 to 2500 nits improves ambient contrast by about 2.2 times, while cutting front surface reflection from 4 percent to 1 percent improves it by about 3.4 times at lower cost and lower power.
Why does a screen look dark through polarized sunglasses?
LCD panels emit polarized light. At certain head angles the polarization axis of the panel crosses the axis of the lenses and the image goes dark. It is unrelated to the brightness rating and is best checked by walking past a demo unit wearing polarized sunglasses before sign-off.
Does brightness measured at the panel match what a viewer sees?
No. Every air-to-glass interface reflects about 4 percent at normal incidence, and an air gap between cover glass and panel adds two more interfaces. Always ask whether the quoted figure was taken at the open cell, behind the cover glass, or at the front of the finished housing.
What should I include in a high brightness display RFQ?
Ask for peak or sustained with the window size, the measurement point in the stack, typical or minimum values, site illuminance measured in lux at the worst hour, the front surface treatment and its reflectance, the dimming range, confirmation that brightness holds at the top of the operating temperature range, and a uniformity figure with a minimum brightness at the end of the warranty term.
Specifying a high brightness screen? TZD Display builds 300 cd/m² indoor signage through to 5000 nit sunlight-readable and IP66 outdoor units, supplied as OEM/ODM with optical bonding and auto-dimming options. Request a quote