905 nm vs 1535 nm laser rangefinder modules

Maintained by ERDI TECH LTD (ERDILRF). This note explains the engineering trade-off between the two wavelength families we supply. It is not a laser safety assessment for your product.

Why the wavelength changes the design

Property	905 nm	1535 nm
Detector	Silicon APD / PIN, widely available	InGaAs or similar, usually more expensive
Atmospheric transmission	Good in clear air, more scattering in fog/dust	Good, with different scattering behaviour
Eye considerations	905 nm reaches the retina; Class 1 operation usually depends on pulse energy, repetition rate and beam expansion	1535 nm is strongly absorbed by water in the cornea and vitreous, so the retinal hazard is much lower; corneal exposure limits still apply
Typical use	Short to medium range, cost-sensitive, high volume	Medium to long range where eye safety at the aperture matters
Source availability	Mature supply chain	Fewer suppliers, longer lead times

The practical consequence: at the same pulse energy, 1535 nm is usually easier to keep inside a lower laser class at the aperture. That does not make it "safe" in the regulatory sense - the finished product still needs a classification and, in most markets, a named safety responsible person.

Range is not a wavelength property

Range depends on:

• transmit pulse energy and receiver sensitivity;
• target reflectivity at the chosen wavelength;
• receiver aperture and beam divergence;
• ambient light and atmospheric conditions;
• the signal-processing threshold and the accepted false-alarm rate.

A 1535 nm module does not automatically out-range a 905 nm module. Compare measurement conditions, not the headline number. ERDI lists per-model conditions on the model pages; for example the LRF200H page separates 90% and 10% reflectivity ranges, and the LRF0306C page documents its 1535 nm conditions rather than promoting a single maximum.

When to choose 905 nm

• The target is cooperative and the working range is short to medium.
• Cost, size and supply continuity matter more than aperture eye safety.
• You already have a silicon detector supply chain and calibrated optics.
• You can keep the beam expanded or the pulse energy low enough for the required class, and you have the test house access to prove it.

When to choose 1535 nm

• The aperture must stay eye-safer without a large beam expander.
• The application is long range with a small receiver aperture.
• The platform is airborne or handheld and the safety case is the limiting factor.
• You accept a higher unit cost and a narrower supplier base.

What we do not claim

• We do not claim a laser class for a finished product.
• We do not claim that 1535 nm is "eye safe" without qualification.
• We do not publish a single range number without its target and visibility conditions.
• We do not treat a module datasheet as a system-level safety file.

Further reading: 905 nm vs 1535 nm comparison, beam divergence and spot size, model index https://erdilrf.com/models/.