Relationship between OD value and protection range of laser safety glasses

Let's first look at the relationship between OD value of laser safety glasses and protection range from the definition

OD value is optical density, which is the logarithm of the reciprocal of transmittance with base 10. The calculation formula is OD=log10(P₀/P), where P₀ is the incident light power and P is the transmitted light power. The OD value indicates the attenuation ability of laser glasses to laser radiation. The higher the OD value, the stronger the attenuation ability to laser, which means the stronger the protection ability. For example, the transmittance corresponding to OD2 is 1%, the transmittance corresponding to OD3 is 0.1%, and the transmittance corresponding to OD4 is 0.01%. By analogy, for every increase of 1 in OD value, the transmittance decreases by one order of magnitude.

Protection range refers to the laser wavelength range that laser safety glasses can effectively protect, usually expressed in nanometers (nm), such as 190-540nm, which means that the glasses can protect lasers in the band from 190nm to 540nm.

The size of the OD value limits the protection ability: within the wavelength covered by the protection range, the OD value determines the degree of protection for each specific wavelength of laser. For example, LaserPair laser safety glasses LP-ATD, 740 - 850nm OD 5+, 780-830nm OD6+, protection range 180-540nm, OD value 5, that is, the intensity of the incident laser within this range can be attenuated by one hundred thousandth, protection range 780-830nm, OD value 6, that is, the intensity of the incident laser within the range of 780-830nm can be attenuated to one millionth, that is, the larger the OD value, the better the protection effect against laser within the protection range.

The protection range limits the range in which the OD value works: that is, a pair of laser protective glasses has a high OD value, but if the wavelength of the laser is not within its protection range, then the glasses cannot provide effective protection. For example, LaserPair laser safety glasses LP-GHP, 180 - 540nm OD 5+, have a protection range of 180-540nm and an OD value of 5, but they cannot protect against lasers with a wavelength of 600nm because 600nm is not within their protection range.

Different wavelengths have different OD values: The same pair of laser safety glasses may have different OD values at different wavelengths within their protection range, because the lenses have different absorption and reflection characteristics for lasers of different wavelengths. Generally speaking, manufacturers will clearly list the OD values at different wavelengths or wavelength ranges in the product specifications so that users can choose the right protective glasses according to the actual laser wavelength used. For example, our LP-YHP-2 laser protective glasses have an OD value of 6 in the 800-900nm wavelength range and an OD value of 7 in the 900-1100nm wavelength range.

In addition, at the boundaries of the protection range, the OD value will gradually decrease. This is because the protection mechanism of the lens for lasers close to the boundary wavelength may change.