1. Laser classification and power limitation
Laser rangefinders must be classified according to the laser safety levels specified in IEC 60825-1 or GB 7247.1 standards. Eye-safe rangefinders
typically employ Class 1 or Class 1M lasers, with their emission power strictly limited to a range that poses no harm to the human eye. For common
wavelengths such as 905nm, both single pulse energy and average power must be controlled below the safety threshold.
If a laser rangefinder uses visible laser, such as a red laser rangefinder, it is the same. It belongs to weak laser and cannot exceed class 3R.
If it exceeds 3R, it becomes a dangerous laser. Therefore, visible laser rangefinders cannot exceed class 3R. If a laser rangefinder uses invisible laser,
such as 905 nanometers, the laser level cannot be classified as class two because it is invisible laser. If the invisible laser is classified as class 3R, it
must emit warnings. This requirement is set in stone. If a laser rangefinder uses invisible laser, it must meet class one, which is the laser level. This
is the same in any country and must meet class one
II. Wavelength selection
Wavebands that are relatively safe for human eyes are preferred. For example, 1550nm laser is largely absorbed at the cornea and hardly reaches
the retina, making it safer than 905nm or visible light wavebands at the same power level. This is also an important reason why military and high-end
civilian rangefinders tend to use 1550nm laser.
III. Pulse width and repetition rate control
By shortening the laser pulse width and controlling the pulse repetition rate, the cumulative effect of laser energy within the eye can be reduced while
ensuring ranging accuracy. The rangefinder needs to limit the maximum duty cycle at the circuit level to avoid continuous high-energy output.
IV. Optical Beam Expansion and Divergence Angle Design
Increase the divergence angle of the laser beam to rapidly disperse the laser energy during propagation and reduce the energy density per unit area.
The emission end of the rangefinder is usually equipped with a beam expander lens group to ensure that the power density of the laser reaching the
pupil has been attenuated to a safe level beyond the normal operating distance.
V. Physical protective structure
A physical barrier or automatic shutter is installed at the laser emission window, which is only opened at the moment of ranging trigger. Some products
are also equipped with an eye proximity sensor, which automatically cuts off laser emission when detecting a human body approaching the emission port,
preventing accidental exposure at close range.
VI. Warning Signs and User Instructions
Mark the laser level, wavelength, and warning messages in a prominent position on the equipment casing. The instruction manual must clearly state
safety guidelines such as prohibiting direct viewing of the laser emission port and avoiding aiming the laser at others' eyes, fulfilling the obligation
of product safety notification.
VII. Inspection, Certification, and Compliance Testing
Before being launched onto the market, products must undergo laser safety certification by a third-party testing agency. This includes testing for the
Maximum Permissible Exposure (MPE), verification of the Accessible Emission Limit (AEL), and safety assessment under abnormal operating conditions,
to ensure that the products meet eye safety requirements in all foreseeable usage scenarios.
