Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

# what is OD?

#### TwistedLight

##### New member
Does more OD=Protection against more Watts? If so, what is the ratio? (Realtionship between OD and number of watts it protects against)
Is higher OD super important?

#### Fiddy

##### Well-known member
OD = Optical density or simple terms absorbance.

Its pretty much a number for the ratio between how much light of a certain wavelength is upon your safety glasses to how much will transmit through your safety glasses.

A higher OD is better, especially with lasers that are 1W+ as it absorbs more of the light instead of letting it transmit through your glasses, into your eyes.

Small percentages of transmittance of such high output lasers such as the 9mm 445nm diodes can add up to quiet a few extra mW's that could transmit your glasses if i direct hit was upon your glasses.

This is my understanding, im sure the people who work in the industry will have something to add

Last edited:

#### TwistedLight

##### New member
OK, so for 1W-2W lasers, what OD should I have?

#### Fiddy

##### Well-known member
at least OD3.

OD 3 will give a transmissions of 2mW if 2,000mW is put upon the safety glasses.

Last edited:

#### pschlosser

##### New member
OK, so for 1W-2W lasers, what OD should I have?

Bear in mind, Optical Density (Absorbance) is also logarithmic. An OD of zero (0) absorbs nothing, no light, and transmits (or passes through the goggles) 100% of the light.

OD = 0, transmits 100% of the light
OD = 1, transmits 10% of the light
OD = 2, transmits 1% of the light
OD = 3, transmits 0.1% of the light.

Our eyes are supposed to be safe exposed to 5mW, so in an ideal situation, you want safety goggles with enough OD to reduce your laser beam brightness to 5mW.

With a 2W laser, as an example, that is 2000mW.

OD = 0, transmits 2000mW
OD = 1, transmits 200mW
OD = 2, transmits 20mW
OD = 3, transmits 2mW

So, if you want to make sure your goggles will be safe enough with a 2W laser, you will need at least goggles with an OD of 3 at the wavelength of the laser light. This is important to make sure the goggles absorb at the target wavelength of light. Because red goggles will NOT filter out red, but may do a great job of blocking blue.

An OD too high, is a problem, too. If you block out too much of the light, then you can't see it at all. And where is the fun in that?

Last edited:

#### Fiddy

##### Well-known member
edit herp derp on my part

Last edited:

#### TwistedLight

##### New member
Bear in mind, Optical Density (Absorbance) is also logarithmic. An OD of zero (0) absorbs nothing, no light, and transmits (or passes through the goggles) 100% of the light.

OD = 0, transmits 100% of the light
OD = 1, transmits 10% of the light
OD = 2, transmits 1% of the light
OD = 3, transmits 0.1% of the light.

Our eyes are supposed to be safe exposed to 5mW, so in an ideal situation, you want safety goggles with enough OD to reduce your laser beam brightness to 5mW.

With a 2W laser, as an example, that is 2000mW.

OD = 0, transmits 2000mW
OD = 1, transmits 200mW
OD = 2, transmits 20mW
OD = 3, transmits 2mW

So, if you want to make sure your goggles will be safe enough with a 2W laser, you will need at least goggles with an OD of 3 at the wavelength of the laser light. This is important to make sure the goggles absorb at the target wavelength of light. Because red goggles will NOT filter out red, but may do a great job of blocking blue.

An OD too high, is a problem, too. If you block out too much of the light, then you can't see it at all. And where is the fun in that?
Thank you for your answer, this is EXACTLY what I was looking for.

Last edited:

#### TwistedLight

##### New member
fiddy, thanks for your help too.

#### Shakenawake

##### Well-known member
this is a pretty helpful thread, I learned something. looks like both my pairs are OD4 for the wavelengths I use

#### TheDukeAnumber1

##### Well-known member
Outer Diameter, O wait different field