905nm Laser Rangefinder: DToF for Short Range
905 nm is the wavelength of nearly every consumer laser rangefinder and most commercial LiDAR. It is not a lesser version of 1064 nm — it is the right choice for a different job.
Why 905 nm dominates short range
- Silicon detectors work. Silicon is sensitive at 905 nm, which means cheap, fast, room-temperature APDs and SPAD arrays. At 1064 nm silicon is nearly transparent; at 1535 nm you need InGaAs.
- Low energy is enough. Short range means strong returns. A few microjoules to a few millijoules suffices, which keeps the transmitter cheap and compact.
- Eye-safe at low energy. At low pulse energies 905 nm can be Class 1, making consumer products possible. The margin is smaller than at 1535 nm, but adequate at low energy.
- Array sensors exist. Direct-time-of-flight (DToF) sensor arrays give depth maps from a single chip, which is what powers consumer depth sensing and short-range LiDAR.
Where 905 nm stops
| Limitation | Consequence |
|---|---|
| Low pulse energy | Falls short beyond a few hundred metres to a few kilometres |
| Atmospheric scattering | Shorter wavelength scatters more in haze, rain and dust |
| Eye-safety limit | Energy cannot be scaled up without leaving Class 1 |
| Detector saturation | Strong close returns can blind the receiver briefly |
The practical ceiling for a 905 nm ranging module is a few hundred metres to a few kilometres, depending on target and optics. Beyond that, the energy cannot be increased without breaking eye-safety limits.
Where 1064 nm takes over
At 1064 nm you can put tens or hundreds of millijoules into a pulse from a diode-pumped solid-state laser, and use a silicon APD for the return. That combination delivers 10–30 km ranging — at the cost of eye safety and a much larger, heavier module.
| 905 nm | 1064 nm | 1535 nm | |
|---|---|---|---|
| Typical range | 0.1–3 km | 3–30 km | 1–10 km |
| Pulse energy | µJ to mJ | 20–120+ mJ | lower than 1064 nm |
| Detector | Silicon APD / SPAD | Silicon APD | InGaAs APD |
| Eye safety | good at low energy | poor at rangefinder energy | good at useful energy |
| Mass | grams to tens of grams | hundreds of grams to kg | hundreds of grams |
DToF vs pulsed ToF
Both time the return; the difference is scale and integration. Direct-time-of-flight sensor arrays integrate the timing electronics per pixel, producing a depth map. Discrete pulsed ToF uses one detector and one timing chain, producing a single range per pulse.
For a depth map at short range, DToF arrays win on size and cost. For a single long-range measurement, a discrete pulsed module wins on energy.
Frequently asked questions
Is 905 nm eye-safe?
At low pulse energies it can be Class 1. At higher energies it is not — the retinal hazard exists because 905 nm reaches the retina. Follow the stated class.
Can a 905 nm rangefinder reach 10 km?
Not practically. Energy is limited by eye safety and detector constraints. Use 1064 nm or 1535 nm for kilometre-class ranging.
Why is 905 nm used in LiDAR?
Silicon detectors, cheap high-speed electronics and eye-safe low-energy operation make dense arrays affordable. Those advantages fade as range increases.
Is 905 nm affected by sunlight?
Yes — the sun is bright at 905 nm. A narrowband optical filter and modulated detection are used to reject ambient light.
Compare wavelengths in 1064nm vs 1535nm, or read 1535nm explained.