1535 nm vs 905 nm: Eye Safety and Range Compared
905 nm and 1535 nm are both near-infrared and both invisible. What separates them is where the light stops in the eye, and that changes the whole safety case.
Why 1535 nm is eye-safe
At 905 nm, the eye focuses the beam onto the retina, and the damage threshold is low. At 1535 nm, water in the cornea and lens absorbs the light before it reaches the retina, so the permissible exposure is far higher for the same hazard class.
That's the entire reason 1535 nm sources exist in rangefinding: more energy within the same class.
The cost of the safer band
Silicon detectors work well at 905 nm and are cheap. At 1535 nm you need InGaAs, which is more expensive and noisier. Atmospheric transmission is a little lower, and the gain medium — Er:Yb glass — stores less energy per unit volume than Nd:YAG at 1064.
So 1535 nm buys safety and pays in detector cost and energy density. Whether that trade works depends on the platform.
When each one fits
905 nm suits short-range, high-rate, cost-sensitive sensing: obstacle detection, industrial distance measurement, consumer instruments. The ER10 family sits at the rate end of the 1535 range, not in that market.
1535 nm suits long range and anything where a person might be in the beam path: handheld optics, UAV payloads, anything sold into a market with strict laser safety enforcement. The ER300 and up are aimed there.
One caution
Class 1 is a property of the finished product, not the source. Changing the optics, the enclosure or the duty cycle changes the product that has to be assessed.
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