Why are 905 nm, 1064 nm, and 1550 nm the dominant wavelengths for LiDAR and LRF?
LiDAR and laser range finders (LRFs) almost always use lasers at 905 nm, 1064 nm, or 1550 nm. Why did these wavelengths become the industry standard? The answer comes down to a mix of physics, regulations, technology maturity, and detector economics.
Why 905 nm, 1064 nm, and 1550 nm 'won'
1. Eye Safety and Regulations
International safety rules (IEC 60825, ANSI Z136) are strict about what light the human eye can safely handle. Light under 1400 nm (including 905 nm and 1064 nm) can pass through the eye's lens and focus on the retina, amplifying the real power reaching sensitive tissue. This means a low maximum permissible exposure (MPE), limiting how much energy you can safely emit (Class 1). 1550 nm and longer wavelengths are absorbed in the cornea/lens—never making it to the retina—so rules allow far more emitted power for Class 1 safety. This gives 1550 nm LiDAR systems a huge advantage in eye-safe long-range sensing.
2. Mature, High-Power Light Sources
- 905 nm: Inexpensive, tiny pulsed GaAs/AlGaAs diodes (10–100 W pulses), highly efficient and available everywhere. Used in consumer, industrial, and automotive LiDAR.
- 1064 nm: Nd:YAG lasers offer extremely high pulse energy (mJ–J), robust and long-proven. Standard in legacy military LRFs and rangefinders.
- 1550 nm: Benefit from telecom-grade Er glass/fiber lasers and EDFAs, letting you scale power safely with mature, stable technology.
3. Detector Economics and Performance
- 905 nm: Works with silicon APDs, which are highly efficient and inexpensive—perfect for mass production.
- 1064 nm: On the edge for silicon detectors, but possible. Some systems leverage specialty Si APDs or move to InGaAs at added cost.
- 1550 nm: Needs InGaAs APDs or coherent receivers; these are higher cost and can have higher dark noise, but prices are falling fast.
4. Atmospheric Transmission and Solar Background
These three wavelengths are all in near-IR 'windows' where atmospheric transmission is high and scattering is manageable. Longer wavelengths (1550 nm) do scatter less via Rayleigh effects, but in real-world weather (fog, rain) Mie scattering and water absorption dominate—both 905 and 1550 nm can struggle, so no wavelength is a perfect solution in tough weather. Narrowband filters and gating remain essential for suppressing sunlight at any wavelength.
| Wavelength | Why Pick It? | Common Uses | Main Limitations |
|---|---|---|---|
| 905 nm | Lowest cost, compact diodes + Si APDs; big supply chain | Consumer/industrial LiDAR, budget auto, handheld LRF | Lower Class 1 power → shorter range than 1550 nm |
| 1064 nm | Very high pulse energy, Nd:YAG legacy systems | Military LRF, designators, some coherent LiDAR | Retinal hazard; not eye-safe for high energy; bulkier optics |
| 1550 nm | Much higher eye-safe Class 1 power, telecom lasers/fiber/EDFAs, long range | Premium auto LiDAR, UAV/airborne mapping, coherent wind sensing | InGaAs receivers (cost/power); system complexity |
Technical clarifications
- '1550 nm always has better range': Only true for eye-safe designs, since legal output is much higher; range depends on all system parameters—not just wavelength.
- 'Longer wavelength means better weather robustness': Only in some cases. In fog/rain, both 905 and 1550 nm degrade for different physical reasons.
- Diffraction gets worse (beams spread more) at longer wavelength, but 1550 nm systems typically use larger optics and can push more power out, so they go farther safely.
- These three bands deliver the best blend of eye safety, mature/emitter technologies, detector compatibility, and atmospheric performance—905 nm for low cost and size, 1064 nm for legacy pulsed energy, and 1550 nm for eye-safe long range and telecom integration.
- No single wavelength is universally superior—system design must balance safety, range, cost, and optical performance for your application.
