OD-Optical Density | How Much Light A Lens Can Block

      Optical Density (OD) in laser safety measures how much light a lens can block at a specific wavelength. It's an important concept because it helps determine how well laser safety glasses can protect your eyes from harmful laser light.

Here's a simple way to understand OD:
 

• High OD: Means the lens blocks a lot of light. For example, an OD of 5 means only 1 out of 100,000 parts of the light gets through.
• Low OD: Means the lens blocks less light.
   

• Comparison of OD and Light Transmittance

  OD	Transmission of light	Attenuation Factor	OD	Transmission of light	Attenuation Factor
  0	1	1	5	0.00001	100000
  1	0.1	10	6	0.000001	1000000
  2	0.01	100	7	0.0000001	10000000
  3	0.001	1000	8	0.00000001	100000000
  4	0.0001	10000	9	0.000000001	1000000000

      The required OD is determined by laser safety standards, such as those found in ANSI Z136.1 in the USA. These standards depend on several factors:
 

• Wavelength of the laser: Different wavelengths (or colors) of laser light can have different effects on your eyes.
• Power of the laser: Stronger lasers need lenses with higher OD to block enough light and keep your eyes safe.
   

      In summary, OD is a measure of how much light a lens can block at a specific wavelength. High OD means better protection, and the required OD depends on the laser's wavelength and power, as determined by safety standards.