Night-time surveillance and contactless biometrics share the same optical problem: the scene must be illuminated with light the human eye does not see, at enough irradiance for a silicon sensor to produce a usable image, and with an angular distribution that matches the lens field of view. Get the wavelength wrong and the subject’s face glows red on camera while a visible red dot betrays the camera’s position. Get the distance budget wrong and the far edge of the field is a dark smear. This white paper is written for security system integrators and biometric device designers, and it sets out the three variables that govern every IR illumination design — wavelength, distance and angular distribution — with the arithmetic that connects them. QUEENDOM’s J-04 5 mm DIP infrared (850/880/940 nm), J-05 2835 infrared and J-06 3535 infrared (730/850/940 nm) emitters are used throughout as worked examples.
1. Why wavelength choice precedes every other decision
Three near-infrared wavelengths dominate security and biometric illumination, and each carries a specific trade-off. The choice is not cosmetic: it determines camera sensitivity, covertness, and — for biometrics, critically — how much of the illumination the subject’s skin absorbs.
| Longueur d'Onde | Relative silicon CMOS response | Covertness to the human eye | Typical use |
|---|---|---|---|
| 850 nm | High (~0.85 of peak) | Low — faint red glow visible | CCTV with visible floodlighting accepted |
| 880 nm | Moderate (~0.60) | Moderate — glow very faint | Discreet CCTV |
| 940 nm | Low (~0.25) | High — effectively invisible | Covert surveillance, iris and face biometrics |
| 730 nm | High (~0.95) | None — clearly visible deep red | Horticulture, special sensing, not covert |
The trade-off is arithmetic. Moving from 850 nm to 940 nm reduces available signal per unit of radiant power by roughly a factor of three. To maintain the same image brightness the designer must either triple the radiant power, triple the exposure time, or accept a shorter working distance. There is no fourth option, and any product claim that promises “940 nm invisible illumination with the same range as 850 nm” is describing a system with approximately three times the emitter count.
| Metric | 850 nm | 880 nm | 940 nm |
|---|---|---|---|
| Eye-safety margin (IEC 62471, same radiant power) | Reference | Slightly better | Best |
| Solar/ambient interference rejection | Weak | Moderate | Strong |
| Atmospheric transmission at 100 m | Reference | Similar | Slightly better |
| Lens coating compatibility | Garantie standard | Garantie standard | May need IR-optimised coating |
| Typical radiant flux per part at 1 A | 700–1,000 mW | 500–750 mW | 350–550 mW |
| Power penalty versus 850 nm for equal signal | 1.0× | 1.4× | 3.0× |
2. The inverse-square law and why range is expensive
Irradiance from a point-like emitter falls with the square of distance. Doubling the working distance quarters the irradiance; tripling it reduces irradiance to one ninth. This relationship is the single most important constraint in IR illumination design, and it is why long-range covert illumination requires large emitter arrays or a beam-shaping optic rather than a simple increase in drive current.
The governing equations for a single emitter are:
“ E = I / d² (inverse square, no optic) I = Φ / Ω (intensity from flux and solid angle) Ω = 2π (1 - cos(θ½)) (solid angle for half-angle θ½) “
where E is irradiance in W/m², I is radiant intensity in W/sr, d is distance in metres, Φ is radiant flux in watts, and θ½ is the half-angle of the emission cone. For a Lambertian emitter, I = I0 · cos(θ), so the on-axis intensity is set entirely by the total flux divided by π steradians.
2.1 Irradiance versus distance
The curve below shows delivered irradiance against working distance for a single J-05 2835 IR emitter at 850 nm and at 940 nm, driven at 350 mA with no secondary optics. The steepness of the fall is the reason security camera specifications should quote illumination range together with the irradiance at that range, not merely a maximum distance.
2.2 The array shortcut
Because irradiance from independent emitters adds, an array of n identical emitters raises irradiance by a factor of n at the same distance. The design equation for an array is therefore:
“ E(d) = n · I0 / d² → d_max = sqrt(n · I0 / E_min) “
Reaching 10 m with a minimum irradiance of 0.5 W/m² and an on-axis intensity of 0.27 W/sr per emitter requires n = 0.5 × 100 / 0.27 ≈ 185 emitters at 850 nm, or roughly three times that number at 940 nm. This arithmetic, not product positioning, is what separates a 10 m covert camera from a 20 m visible-illumination camera.
3. Angular distribution and matching the lens field of view
An illuminator and a camera lens are one optical system. The illuminator’s intensity distribution must cover the lens field of view at the working distance, and it must do so without wasting the majority of its power outside the imaged region.
| Distribution type | Half-angle | Characteristic | Best fit |
|---|---|---|---|
| Narrow beam | 10°–20° | High on-axis intensity, small footprint | Long-range identification, 850 nm |
| Medium beam | 30°–45° | Balanced coverage | General CCTV, access control |
| Wide beam | 60°–90° | Uniform near-field coverage | Indoor rooms, kiosk biometrics |
| Lambertian | 60° (half-angle at 50 %) | No optic, emitter-native | Very short range, dense arrays |
| Batwing / shaped | Optiques spéciales développées sur demande. | Flattened centre, raised edges | Correcting inverse-square falloff on a plane |
The batwing distribution deserves emphasis because it solves the central uniformity problem of IR illumination. A Lambertian emitter produces an on-axis hot spot and dark corners on a flat scene. A shaped optic that redistributes energy towards the edges compensates for both the inverse-square distance variation and the cosine foreshortening at the field edges, producing a uniform irradiance plane.
4. Biometrics: the additional constraints
Face recognition, iris recognition and liveness detection impose requirements beyond simple illumination.
Face recognition performs best in the 850 nm band for indoor access control because silicon sensitivity is high and skin reflectance is relatively flat. In direct sunlight, ambient near-infrared floods the sensor and the 850 nm band offers poor contrast; moving to 940 nm gains solar rejection because the solar spectrum’s near-infrared continuum is attenuated by atmospheric water absorption relative to the LED band, and the camera’s narrow bandpass filter can then isolate the emitter’s contribution.
Iris recognition requires the iris texture to be visible through the cornea, and 850 nm provides good contrast between the iris stroma and the pupil. Because the iris is highly structured, uniform illumination across the iris disc matters more than raw power; non-uniform illumination produces specular highlights that corrupt the code.
Liveness and anti-spoofing increasingly uses multi-wavelength illumination. A 940 nm channel combined with an 850 nm channel produces differential reflectance information that distinguishes skin from printed photographs and screens.
| Biometric modality | Preferred wavelength | Illumination requirement | Typical working distance |
|---|---|---|---|
| Face recognition, access control | 850 nm | Uniform over face, 0.3–1.0 W/m² | 0.4–1.5 m |
| Face recognition, covert/outdoor | 940 nm | High uniformity, ambient rejection | 0.5–2.0 m |
| Iris recognition | 850 nm | Very uniform over iris disc | 0.2–0.5 m |
| Palm vein / finger vein | 850 nm (transmissive) | High irradiance through tissue | Contact–0.1 m |
| Eye tracking | 850 or 940 nm | Low retinal hazard, high uniformity | 0.3–1.0 m |
| Multi-spectral liveness | 850 + 940 nm | Two synchronised channels | 0.4–1.0 m |
5. Product mapping
The three families cover the whole range of security and biometric illumination requirements, with the choice driven by package size, flux and mounting method.
| Requirement | Recommended part | Package | Peak | Typical radiant flux | Notes |
|---|---|---|---|---|---|
| Discrete through-hole illuminator | J-04 5 mm DIP IR | 5 mm DIP | 850 / 880 / 940 nm | 40–80 mW @ 100 mA | Legacy boards, easy hand assembly |
| Dense SMD panel for CCTV | J-05 2835 IR | 2835 SMD | 850 / 940 nm | 500–900 mW @ 350 mA | Compact, high density per area |
| High-power narrow beam | J-06 3535 IR | 3535 ceramic | 730 / 850 / 940 nm | 700–1,000 mW @ 1 A | Ceramic body, MCPCB required |
| Long-range covert surveillance | J-06 3535 IR × array | 3535 ceramic | 940 nm | Array of 100–400 parts | Paired with narrow beam optic |
| Kiosk face biometrics | J-05 2835 IR | 2835 SMD | 850 nm | 500–900 mW @ 350 mA | Ring or bar layout for uniformity |
| Dedicated sensing / horticulture | J-06 3535 IR | 3535 ceramic | 730 nm | 600–850 mW @ 1 A | Not for covert use — visible deep red |
5.1 Junction temperature and output stability
IR emitters used in continuous CCTV operation run hot, and output falls as junction temperature rises. The drift is approximately -0.3 to -0.5 %/K for 850 nm AlGaAs devices and slightly steeper for 940 nm. A camera head sealed to IP66 with no active cooling can see 40 K of self-heating, which costs 12–20 % of the illuminator output. This is the second reason that thermal design, not nominal flux, determines the real range figure.
| Condition | Tj (typ.) | Relative output | Effect on usable range |
|---|---|---|---|
| 25 °C case, pulsed | 35 °C | 100 % | Reference |
| 25 °C case, continuous | 55 °C | 91 % | -5 % range |
| 55 °C case, continuous | 85 °C | 79 % | -11 % range |
| 70 °C case, continuous | 100 °C | 71 % | -16 % range |
6. Common mistakes and how to avoid them
| Mistake | Consequence | Correction |
|---|---|---|
| Specifying range without irradiance at that range | Unverifiable and usually optimistic claim | State distance, irradiance and lens aperture together |
| Using 940 nm and expecting 850 nm range | Image three times dimmer than expected | Triple emitter count or reduce working distance |
| Beam wider than the lens field of view | Most power illuminates outside the image | Match beam angle to the lens FOV at working distance |
| Ignoring skin reflectance differences | Biometric failure for darker skin tones | Budget irradiance for the lowest expected reflectance |
| No bandpass filter on the camera | Daylight and street lighting contaminate the image | Fit a narrow bandpass filter centred on the emitter |
| Neglecting thermal derating in a sealed housing | Range drops after minutes of operation | Derate 12–20 % for self-heating in sealed heads |
| Overlooking IEC 62471 classification | Non-compliant product, possible eye hazard | Classify the full illuminator, not just the emitter |
| Using 730 nm for covert applications | Visible deep red glow | Reserve 730 nm for sensing applications only |
7. Verification and test methods
- Spectral and radiant flux measurement — verify peak wavelength and radiant flux on a calibrated integrating sphere at the production drive current and at the production case temperature, since peak wavelength shifts with temperature at roughly 0.25–0.35 nm/K.
- Irradiance mapping — place a calibrated radiometer at the plane of interest and measure a grid covering the imaged area at the design working distance. Report minimum, maximum and uniformity ratio.
- Beam profile measurement — use a goniometric scan to confirm the angular intensity distribution matches the lens field of view, and to detect central hot spots that will saturate the sensor.
- End-to-end image-quality test — capture grey-scale test targets at the specified working distance under the specified illuminator with the production lens and sensor. Measure modulation transfer function and signal-to-noise ratio, which are the metrics the end user actually experiences.
- Thermal soak — operate the sealed camera head at rated ambient for at least two hours and re-measure irradiance to quantify self-heating drift.
8. Conclusion and selection guidance
For most indoor access control and kiosk biometrics, J-05 2835 IR at 850 nm offers the best combination of high silicon response, compact footprint and dense array capability at short working distances. Move to J-06 3535 IR when a narrow beam and high per-emitter flux are needed for long-range identification, and select the 940 nm variant when covertness or ambient rejection matter more than radiant efficiency — accepting the roughly three-times power penalty that comes with it. Reserve J-04 5 mm DIP IR for through-hole boards and low-density legacy designs. Design the array from the inverse-square equation rather than from a product range table, match the beam angle to the lens field of view, and derate for thermal drift in sealed housings.
9. Referenced standards
- IEC 62471 — Photobiological safety of lamps and lamp systems
- IEC 60825-1 — Safety of laser products (applies where collimated IR sources are used)
- IEC 60529 — Degrees of protection provided by enclosures (IP code)
- IES LM-80 — Approved method: measuring luminous flux maintenance of LED light sources
- IES TM-21 — Projecting long-term lumen maintenance of LED light sources
- ISO/IEC 19794 — Biometric data interchange formats (context for biometric system requirements)
- ONVIF Profile S / Profile T — Network video interface specifications (device integration context)
10. Contact us
QUEENDOM supplies the J-04 5 mm DIP infrared, J-05 2835 infrared and J-06 3535 infrared families from stock in 850 nm, 880 nm and 940 nm variants, together with reference illuminator layouts and irradiance mapping templates. Our component engineering group can provide angular distribution data and thermal derating curves on request. Contact us for samples, driver recommendations and application support.
Related products and applications
The infrared emitters and the luminaires that house them are listed below.
- Infrared emitter LED (J-04)
- Infrared emitter LED (J-05)
- Infrared emitter LED (J-06)
- Application overview: LED components application solutions
- More technical papers: LED knowledge resources