Survey the site, not just the number
Record orientation, times of direct sun, shade and reader position. A shop window differs from open air: glass can reflect and affect heat. Photograph the actual viewing axis. Visit when light is unfavorable, not only on a cloudy morning.
Test with content
Compare the smallest required text, light and dark areas and fine details. A white test image does not establish menu readability. Check side views and reflections. Define which information must be recognized from each position, then record observations.
Evaluate brightness and heat together
A peak figure says little about sustained use under solar load. Ask what conditions apply and whether thermal protection dims or stops the screen. Evening use needs suitable dimming to avoid excessive glare. Testing and limits must match the installation.
EXAMPLE / FENSTER-A
Check price and promotion duration from three positions.
The completed example shows how to record price and promotion duration at three viewing positions. Compare A, B and C, then plan the next check. Use your own observations for your location.
EXAMPLE SHEET / A-v1
“Brightness: stated for normal mode.”
Measurement direction, glass and thermal conditions are missing in this example. A real offer needs actual model-specific original documentation.
BIPM / 2019 / §2.3
“… in a specified direction at a specified point …”
This short original fragment from the luminance definition specifies direction and point. The source’s following note requires reporting specific measurement conditions with the result. Measurement direction and documented setup therefore belong alongside a figure; example sheet A-v1 leaves them open.
Original source: printed page 4, definition 2.3 and note 1. Scope: photometric definition and measurement conditions; no model approval, glass test or readability threshold.
What the source explains—and what it does not
The BIPM document “Principles Governing Photometry” defines photometric quantities and units. A figure in cd/m² (nits) describes luminance; the source sets no acceptance limit for this storefront. Content readability needs assessment under documented project conditions. The DWD context supports site planning but confirms neither device brightness nor temperature approval.
DWD data, site questions and calculation limits ↗
- Display: same content and mode; datasheet conditions still open.
- Glass: part of the installed system; consider reflection separately from display figures.
- External light: incidence and reflection change; A, B and C mark the viewing positions in the example.
Front-on · 2 m · overcast
Price and promotion duration identified.
Applies only to this position and time.
Side-on · 2 m · clear sky
Price identified, promotion duration uncertain; building reflection across the small line.
Position and light changed together. Cause not isolated yet.
Queue · 3 m · low sun
Promotion duration not identified. External reflection and greater distance recorded.
No evidence that more brightness alone resolves it.
Completed example record
- Record / status
- FENSTER-A · open, not accepted
- Site / task
- Shop window with a glass frontage; identify price and promotion duration from the queue.
- Date / participants
- Example date: July 15, 2026; three observation times.
- Setup / content
- Demo device A behind uncoated example glass; price template v3, same type and content in all three observations.
- Documentation / settings
- Example sheet A-v1 specifies “normal mode.” Measurement direction, front glass, temperature and derating are undocumented. Same mode; numeric setting unverified.
- Observation / evidence
- Viewing positions A, B and C in the diagram. Add photos, device settings and measurement methods when checking your own location.
- Acceptance criterion
- Both price AND promotion duration must be readable at every intended position. Example project criterion, not a universal threshold.
- Decision / next review
- Example result: B and C are not yet complete. Request mode and glass conditions from the supplier, then repeat position B with the same content.
Explain the difference before adjusting
- Record what stayed the same: content v3 and mode. This does not establish constant luminance; derating is unresolved.
- Separate changes: B differs in viewing direction and light. First repeat the intended position with recorded content, mode, glass and time. Then change only one controllable condition.
- Do not claim a cause prematurely: without model conditions and a repeat check, glass, layout, viewing direction and device state remain open causes. Readable prices from the front do not establish that the same prices are readable from the queue.
- Take your own reading positions, documentation gaps and next check into the brief. Record acceptance only against the agreed criteria.
The project brief imports the brightness questions from the evidence check. Add your own site observations there. Acceptance requires the agreed criteria to be checked at the location.
Open the worked example
CHECK YOUR OWN LOCATION
Planning steps and acceptance checks
Use A, B and C as a starting point for checking your location. Mark the required viewing positions and times with difficult light. Display the planned layout with the longest product names. Record readable information, reflections and dimming. Request measurement conditions and operating limits from the supplier, then use these to define the requirement for your installation.
| Aspect | What to check |
|---|---|
| Read actual content from every marked position | Essential text and prices are recognizable |
| Document unfavorable light conditions | Photos, time and observations are traceable |
| Ask about dimming and thermal limits | Conditions and possible restrictions are documented |
What to bring to the project discussion
| Aspect | What to check |
|---|---|
| Direct sun | Real content at the worst time of day |
| Behind glass | Reflection, heat and ventilation |
| Night operation | Dimming and intrusive light |
| Continuous use | Thermal behavior and derating |
Three concrete next steps
- Document sun and reader positions.
- Evaluate a sample on site.
- Request measurement conditions and limits.
Limit of this recommendation
A generic indoor/outdoor table does not replace site acceptance. Agree on reading criteria for the content and viewing positions.
Sources & context
- BIPM — Principles governing photometry (2019)
Photometric terms and the SI unit of luminance. No recommended brightness figure for display installations.
Request documents for the exact model and assess the planned installation before acceptance. Prepare a correction