2.1 · The display and the two viewing tasks
Chapter 2: The display and the two viewing tasks
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PDF deck A-P17 · 14 slides · 19 October 2026 · Development edition. This PDF matches the chapter video. Future PDF updates may be newer than the video.
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Chapter 2 · Page 1 of 4
What we are doing in this chapter
A display in an NVIS installation has to support two tasks: reading display information and seeing the outside scene. Establish how the operator will read the display: below or around the goggles, through the goggles, or using a combination of arrangements. In a conventional look-under arrangement, the operator looks below the goggles to read the display with unaided vision, then looks through the goggles to view the outside scene. This is the arrangement used to introduce the course. Other systems use different viewing geometry or projected imagery. The look-under example is a starting configuration, not a rule for every NVIS display.
The engineering task is to provide readable display information while controlling the light that could interfere with the view through the goggles. Both tasks serve the same operator. The observer is the person. The NVIS receiver is the light-sensitive part of the night vision equipment. The eye and receiver have different spectral responses, so visible brightness alone cannot establish NVIS compatibility.
Your role may cover only part of the system. You may supply filter material or backlight rails, build modules, or enhance a display with AR glass, EMI shielding and optical bonding. You may not have every installation detail. Use Case Alpha for missing context, label assumptions and unknowns, and identify the requirements and evidence that apply to your scope. Understanding the interactions still helps your process and product development.
Visible opacity is not an infrared measurement. A material that looks completely opaque to the eye can transmit substantial near-infrared light. A black-looking cover or mask is therefore not automatically an NVIS barrier. Check its transmission spectrum over the receiver-relevant wavelengths. The spectral reasoning is developed in Chapter 8 and the material examples in Real glass, LED and measurement examples.
By the end of this preview chapter, you should be able to:
- Describe the display-reading task and the outside-scene task for an installation.
- Sketch the wanted display image, display light reaching the goggles, and direct and reflected ambient-light paths from nearby and distant sources.
- Separate daylight legibility, night legibility, NVIS compatibility and reliable operation.
- List the requirements and evidence still needed before choosing a filter or declaring compatibility.
Your working output: one labeled light-path sketch and an initial requirements-and-evidence list. Use your own installation or Case Alpha, the hypothetical color LCD introduced in Chapter 01. You do not need to calculate weighted radiance or choose a filter yet. Later chapters develop those methods.
Displays viewed through goggles
Some displays are intended to remain readable through the night vision system. Head-up displays are an important example. MIL-STD-3009 Appendix C.7.6 describes HUD imagery viewed through Type I NVIS and explains both a lower radiance limit for visibility and an upper limit to control interference. Section 3.1.5 describes the Class C green transmission window used to support certain green HUD imagery. See S2.
For that arrangement, some display light reaching the receiver is the wanted image. The design must preserve its readability while controlling other light that could impair the outside scene. Evaluate the display spectrum, receiver response, focus and viewing geometry together. NVIS compatibility alone does not establish that a conventional panel can be read through goggles.
The term Type I direct-view NVIS describes the night vision architecture; it does not mean that every instrument-panel display is intended to be read through the goggles. Chapters 4 and 6 develop these distinctions.
The observer, receiver and light paths
Simple line drawings make the light paths easy to follow. The realistic cockpit illustration provides context; it is AI-generated and does not identify qualified equipment.
Four views of the installation
Follow scene 02.3 in the video: the rays draw as each route is explained. These schematic views also appear in the follow-along PDF. Expand a view to inspect it.
Light paths: the installation
Schematic routes, not a scaled optical ray trace.
Light paths 1 and 2: display light
Through-goggle displays: distinguish intended useful imagery from unwanted light and leakage.
Light path 3: reflected ambient light
Examples of possible routes. Check the actual surface geometry and spectrum.
Light path 4: direct ambient light
Direct light may carry useful information or cause interference; evaluate the task.
The display must convey the required information at the specified distance, angle and ambient illumination. At the same time, the installed lighting must support the outside-scene task through the intended goggles. Light that appears faint to the eye may still affect the receiver. Display-originated light may reach the goggles directly, through gaps, or after reflection from a canopy or window.
Mark the operator, display, goggles and outside scene on your sketch. Add a nearby lamp or indicator and a distant source such as a streetlight or vehicle light. Show the useful outside-scene path through the goggles. For the look-under example, trace four additional path groups:
| Path | What to draw | What to ask |
|---|---|---|
| Wanted display image | Display to the operator’s unaided eye | Can the operator read the required symbols, grayscale and colors? |
| Display-originated light toward the goggles | Display face and leakage paths to the goggle objective | Which spectra, operating states and gaps contribute unwanted light? |
| Reflected ambient light | Nearby lamp or other source to the display/canopy, then toward the eye or goggles | Which reflections remain when the backlight is off? |
| Direct ambient light | Nearby lamp/indicator or distant streetlight/vehicle light directly to the eye or goggles | What useful information or unwanted light reaches the receiver without reflecting from the display? |
EXIT-sign example. An illuminated EXIT sign inside the cabin can reflect from the display surface toward the unaided eye and, where the geometry permits, into the goggles. The reflected sign can remain visible over the display image with the backlight off. Keep both the display and operator inside the window on the sketch, and distinguish this reflected path from sign light entering a receiver directly.
Direct ambient light from nearby and distant sources can reach the eye or goggles without first reflecting from the display. The same source can also contribute reflected light. Distance alone does not determine interference: identify the source spectrum, light reaching the receiver, direction and any shielding or obstructions. Label useful scene information, unwanted light and paths that still need evaluation. A distant light may itself be something the operator needs to identify. Include at least one nearby and one distant source in the sketch, with their direct and reflected paths.
If your installation requires reading a display through the goggles, add its intended display-to-receiver path and distinguish that wanted imagery from unwanted light. Do not treat every display-to-goggle path as interference.
Add neighboring indicators and other possible infrared emitters, including IR illuminators used with cameras, infrared remote controls, and infrared touch systems. Not every camera or touch system emits infrared light, so check the actual equipment in the installation. A treatment that controls one path may leave another unaffected. Keep this sketch for Chapter 7. Chapter 13 develops the paths inside the display.
Chapter 2 · Page 2 of 4
Four separate requirements
| Requirement | Quantity or evidence | Why it remains separate |
|---|---|---|
| Daylight legibility | Luminance, ambient contrast, glare, viewing geometry and task performance | More light output alone may not overcome reflected ambient light |
| Night legibility | Minimum useful luminance, black level, grayscale, color and stable steps | A low measured white level does not prove readable symbols |
| NVIS compatibility | Applicable weighted radiance, chromaticity and installation evaluation | Human-visible brightness does not measure receiver-sensitive emission |
| Reliable operation | Temperature, aging, faults, transitions and manufacturing control | A room-temperature prototype is one configuration at one condition |
Terms for this preview. Luminance is luminous intensity per unit projected area in a specified viewing direction; its unit is cd/m², also called nits. Contrast describes the distinction between a symbol and its background under specified conditions. NVIS weighted radiance combines measured spectral radiance with the standard’s specified receiver-response function. It is a different result from luminance or contrast. Chapter 8 develops the quantities and units; Chapter 9 develops the weighting and measurement.
Sources: S1, S2. The installation exercises below are teaching applications.
Exercise: a display looks dark through the goggles
A supplier reports that a display meets its daylight white-luminance target and supplies a photograph in which it looks dark through goggles. Does this establish compatibility? Before reading the discussion, list at least one missing item for each of the four requirements above.
Discussion: evidence still needed
The photograph illustrates the arrangement. Its appearance also depends on exposure, goggle gain and image processing; without their settings and suitable measurement evidence, darkness in the image is not a quantitative acceptance result. Request the receiver identity, display pattern and operating luminance, viewing geometry, ambient conditions, and calibrated spectral measurements tied to the applicable criteria.
First establish whether the display is meant to be read below the goggles or through them. If through-goggle reading is required, a dark image may indicate loss of useful display information. Then ask whether the operator can read the required information through the intended viewing path and identify the necessary outside-scene detail through the goggles. Check night readability, reflected paths, operating modes and environmental conditions as separate items. A brightness target and a dark photograph do not complete those checks.
Exercise: turn the viewing task into a test
Draft a requirement for reading a warning on the display and then identifying a required outside-scene feature through the goggles. Name the warning and outside feature, viewing distance, angles, ambient lighting, goggle arrangement and any required response time. State explicitly whether display information is read below the goggles or through them. Mark missing acceptance limits as unresolved.
Add evidence to your sketch using this starter:
| Requirement to complete | Evidence to plan | Decision still needed |
|---|---|---|
| Read the specified warning using the intended viewing path at the stated distance and angles | Task-based readability evaluation with the required symbols, viewing optics and lighting | Symbol details, response time and acceptance criterion |
| Identify the specified outside feature through the intended goggles | Installation evaluation with the defined scene and surrounding lights | Feature, scene conditions and acceptance criterion |
| Meet the applicable display-emission criteria at the prescribed test condition | Calibrated spectral measurements and a report identifying the standard criteria | Applicable Type/Class, category and test conditions |
| Maintain performance across required modes and environmental conditions | Defined tests for temperature, transitions, faults and other specified conditions | Operating envelope and pass/fail criteria |
Keep luminance, contrast, weighted radiance and task performance as separate results. This is a starter for a requirements record, not a completed acceptance specification. Chapter 21 turns the record into a measurement and verification program.
Chapter 2 · Page 3 of 4
Case Alpha: teaching inputs and assumptions
Case Alpha is a hypothetical transmissive color LCD used throughout the course. These inputs describe the training case; they are not an FPD.DEV product specification or universal NVIS limits.
| Input | Teaching value or assumption |
|---|---|
| Display / receiver | Color LCD / Type I, Class B |
| Day / night operating luminance | 1,200 / 0.05 cd/m², or nits |
| Daylight model | 100,000 lx incident illuminance and a Lambertian diffuse-reflection model |
| Temperature / viewing study | −20 to +60 °C / ±30° from the display normal |
The display normal is perpendicular to its face. The diffuse-reflection model describes a reflected background; it does not represent a sharp mirror-like solar reflection. A directional glare case needs its own geometry and evaluation.
Keep the display’s operating targets separate from the standard’s reference test luminance. Test settings and limits come from the applicable criteria, not automatically from the desired day or night brightness. Chapter 4 explains the Type/Class selection and requirement boundary.
The Case Alpha input pack defines additional teaching criteria, driver constraints, candidate architectures and model boundaries. Label each entry as a selected requirement, a teaching assumption or an unresolved acceptance condition. For a real project, the acquiring activity or responsible requirements owner must define missing acceptance criteria. Chapters 18–20 develop the control and daylight budgets.
Reflection control is part of the system
Turn the backlight off in your thought experiment. Ambient sources can still reflect toward the eye or goggles. Follow each boundary: the AR-coated front surface, cover/filter, filter/bond, bond/LCD, and the interfaces within the LCD. Arrows identify possible routes; they do not imply equal reflected power.
An air gap creates two material-to-air index mismatches. These can reflect much more than a well-matched optical bond. Bubbles or delamination can restore an unwanted gap. The impact may be reduced daylight contrast, a reflected image over symbols, or unwanted light reaching the goggles at night. Spectrum and viewing geometry determine the result.
AR coatings reduce the combined reflection from their thin-film interfaces over a designed wavelength and angle range. Optical bonding reduces index mismatch at buried interfaces. Neither makes the complete stack reflection-free. A filter can attenuate selected wavelengths on the incoming and returning passes when the reflection occurs behind it. A reflection in front of that filter does not receive the same two-pass attenuation.
Check refractive indices, coatings, wavelength, angle and polarization. Visible performance alone does not establish the behavior over the wavelengths detected by the goggles. Mark each interface on your sketch and identify the sources and receivers of its returned light.
Inspect the optical interfaces
Chapters 7, 13, 14, 15 and 19 develop the paths, materials and verification.
Check your chapter output
Your sketch should identify both viewing tasks, the intended display-viewing arrangement, the wanted outside-scene path, and the relevant display-related paths. If display imagery must be read through the goggles, identify that wanted path explicitly. Your requirements list should distinguish the four requirements, name evidence for each, and leave missing acceptance values clearly marked. Explain why dimming alone cannot remove a reflection from a neighboring lamp.
Continue your learning: Chapter 6 — How image-intensifier goggles work · Chapter 7 — The display in the shared lighting environment · Chapter 13 — Follow the light from backlight to viewer · Chapter 21 — A practical measurement and verification program.
Chapter 2 · Page 4 of 4
Which night-vision receiver?
Identify the actual receiver before extending Case Alpha to another system. Chapter 5 compares intensifiers, digital cameras, SWIR, thermal and fusion. A receiver map separates the sensing path from the display-output path. The specified NVIS result does not automatically cover every device marketed as night vision.
Next: Chapter 3 — From MIL-L-85762A to MIL-STD-3009
We’ll look at how the standard evolved and what that means for display requirements.
I’m Diggy Breiling. Thank you for joining me.
FPD.DEV, the Future of Display and Systems Development.
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