Laser pointer discussion. Read/write reviews of laser pointers and laser pointer companies. Learn about all types of laser pointers and lasers

 Welcome to Laser Pointer Forums! If you are looking for a laser pointer or want to compare different laser pointer companies, you may want to check out the LPF Laser Pointer Company Database. The link will open in a new window for your convenience.

One laser store meets all your needs

 Laser Pointer Forums - Discuss Laser Pointers What OD for what mw?

LPF List of Laser Pointer Companies (link opens new window)

11-13-2008, 01:07 AM #1
 Class 1 Laser Join Date: Nov 2008 Posts: 89 Rep Power: 9
BeavRat
Class 1 Laser

Join Date: Nov 2008
Posts: 89
Rep Power: 9
What OD for what mw?

Is there some sort of chart showing what OD rating you need in goggles to protect from the mw of a laser? So if you have N amount of mw, what Od do you need?

Thanks

LPF List of Laser Pointer Companies (link opens new window)

11-19-2008, 04:23 AM #2
 Class 1 Laser Join Date: Nov 2008 Posts: 89 Rep Power: 9
BeavRat
Class 1 Laser

Join Date: Nov 2008
Posts: 89
Rep Power: 9
Re: What OD for what mw?

Come on guys!!

11-19-2008, 04:45 AM #3
 Class 2M Laser Join Date: Sep 2007 Posts: 977 Rep Power: 80
FrothyChimp
Class 2M Laser

Join Date: Sep 2007
Posts: 977
Rep Power: 80
Re: What OD for what mw?

Since you don't want to research it (as it's all over the safety section), the actual calculation is:

OD = log[sub]10[/sub](E[sub]i[/sub]/E[sub]t[/sub])

Where E[sub]i[/sub] is the incident beam energy (generally in W/cm[sup]2[/sup]) and
where E[sub]t[/sub] is the transmitted beam energy (generally in W/cm[sup]2[/sup])

Because you are dividing E[sub]i[/sub] by E[sub]t[/sub] you have a ratio and thus can use any power rating as long as the incident and the transmitted power are the same units.

Here is an example:

Laser Maximum Output: 200mW
Maximum Transmitted Power: 5mW (keep the exposure at or below Class IIIa levels)

OD = log[sub]10[/sub](200mW/5mW)

OD = log[sub]10[/sub](40)

OD = 1.602059991

Thus if I have a 200mW laser and I want to allow no more than 5mW to pass through the lens I will need protective eyewear rated at least OD 1.60205991 at the laser wavelength.
__________________
The Frothy Chimp
Cynic Extraordinaire
Why yes, I am a rocket scientist

Good whiskey, fine cigars, long legged women and blues guitar.
That's what I like.

The strong shall stand, the weak shall fall by the wayside.

12-11-2008, 11:43 PM #4
 Class 3R Laser Join Date: Sep 2008 Location: Williamsport, MD Posts: 1,808 Rep Power: 111
randomlugia
Class 3R Laser

Join Date: Sep 2008
Location: Williamsport, MD
Posts: 1,808
Rep Power: 111
Re: What OD for what mw?

I alway heard divide by 10. Example: 100mW through OD2 would be 1mW. 300mW throughe OD3 would be 0.3mW
__________________

12-17-2008, 03:36 AM #5
 Class 1 Laser Join Date: Dec 2008 Posts: 50 Rep Power: 9
Ironbar
Class 1 Laser

Join Date: Dec 2008
Posts: 50
Rep Power: 9
Re: What OD for what mw?

Quote:
 Originally Posted by FrothyChimp Since you don't want to research it (as it's all over the safety section)
Heh, you enabler Frothy!

Seriously though, why don't people research more before asking questions?

I take pride in being able to find my own answers, without having to pose public questions. Posing a public question is kinda like admitting defeat - I lost my personal battle of finding the answers for myself.

12-22-2008, 07:57 PM #6
 Banned Join Date: Apr 2007 Location: Cupertino CA Posts: 1,076 Rep Power: 0
Laser_Ben
Banned

Join Date: Apr 2007
Location: Cupertino CA
Posts: 1,076
Rep Power: 0
Re: What OD for what mw?

Quote:
 Originally Posted by randomlugia I alway heard divide by 10. Example: 100mW through OD2 would be 1mW. 300mW throughe OD3 would be 0.3mW
Not exactly, at some OD, that does work. But for other values it would not work. Use the equation listed above.

12-22-2008, 08:54 PM #7
 Class 4 Laser Join Date: Oct 2007 Location: Oregon, USA Posts: 5,477 Rep Power: 1792
Class 4 Laser

Join Date: Oct 2007
Location: Oregon, USA
Posts: 5,477
Rep Power: 1792
Re: What OD for what mw?

You can also calculate how much power will be transmitted through the filter using:

P[sub]transmitted[/sub] = *P[sub]incident[/sub] * 10[sup]-OD[/sup]

Ex:

Your laser outputs 100mW, and you have a filter with OD = 2.5 for that wavelength. *The power of the filter's transmitted light will be:

0.100W * 10[sup]-2.5[/sup] = 0.00032W = 0.32mW

So it isn't quite just divide-by-10.
__________________
You must spread some Reputation around before giving it to <person> again.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

All times are GMT. The time now is 07:27 PM.

 -- DarkShadows V5 -- Responsive LPF -2562016 -- Default Style Contact Us - Laser Pointer Forums - Archive - Top