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Is this laser safe? Help!


New member
Jun 1, 2018
So I'm trying to build a prototype product in my spare time, part of which uses a laser torch (a bit like a laser genetics ND5). It needs to be as bright as possible but still safe (class 2m).

Does anyone know the maximum power density (mw/cm2) allowed for a laser to still be in class 2m?

Also, I guess this has to be the power density at the narrowest point of the beam (i.e. directly when it exits the torch lens) - right? I which case, I figure to make it brighter without going over the power density limit for 2m, I can just increase the size of the exit lens. Right?

Is there anything else I can do to increase brightness while keeping the thing in class 2m?

Thanks, and sorry for my naivety!


Well-known member
May 14, 2011
Short answer-- in a word--no. You are mixing apple and oranges.
There isn't any way to make a Class 2M laser of any given wavelength brighter than a Class 2M laser of that wavelength and have it still be a Class 2M laser---common sense should tell you that.
Is like asking is there a way to make 50MPH faster than 50MPH or an inch a little longer or shorter than an inch and still be an inch.
Laser Class is based on physical reality/a reality as defined within and by Physics, independent of any individual/person/observer, not some variable make believe in some daydream or imagining. lol

Class 2 lasers are limited to 1mW. It is what it is -- the maximum limit of amount of light that can enter the eye.
There is no way to make a 1mW laser higher output and and visually brighter and still be a 1mW laser .

Output power is mW of a wavelength in nm---a physical description of energy and wavelength, completely independent of/from any human observers eyes/brain visual system.
Brightness is a characteristic of the human visual system and is depends upon several afctors the most commonly considered is relative brightness of different wavelengths. See Relative Brightness Calculator here: https://slickscreen.github.io/laser-tools/brightness/
Maximum visual brightness can only be acheived by using the brightest wavelength to the human visual system -- commonly available laser pointers is 532nm green which is about 10X brighter than same mW output of 450nm blue which is about 10X brighter than same output of 405 nm blue/violet Anything other than 532nm green will be less bright visually.
A 520nm direct diode is close, 0.82 as birght as 532nm. and peobably would be easier for you easier to use in making an apparatus of whatever kind than a DPSS 532nm which is 1.22X brighter than 520nm.

"Example Calculation of Maximum Permissible Exposure (MPE)
This example will show you how MPEs are calculated using the tables in standard 60825-1:2014.
A normal laser user will not typically be required to make such calculations but it is useful for your understanding to see how these calculations are made and how they relate to laser CLASS.
What is the MPE for a continuous wave visible laser? i.e. What is the safe level of power for a visible laser if incident on an unprotected, fully dilated pupil?
1. For MPE calculations a fully dilated pupil is assumed to be 7mm in diameter
2. Look up the formula for the MPE from the tables in the EN 60825-1:2014 standard andwe find it is MPE = 18t0.75 J/m squared
3. Use the value 0.25s for t as this is the time it takes for the eye to react to an uncomfortable stimulus (blink reflex).
4. putting in t = 0.25s we find the MPE = 6.36 J/m squared
5. Remember that power = energy/time so to convert this value to irradiance (Wm-2), we divide 6.36 J/m squared by the time 0.25s, which gives us a value of 25.4 W/m squared. The safe irradiance is 25.4W/m squared for a visible laser. MPE is 25.4 W/m squared.
6. How does this equate to the power level which can enter the eye and not cause damage?
The area for the pupil of diameter 7mm using 𝜋𝑟 squared is 3.85 x 10-5m squared,.
Calculate how much power enters the eye. 25.4 W/m squared X 3.85 x 10-5m squared ≈ 1 mW
Hence all CLASS 2 lasers must be 1mW or less so that the blink reflex can help to protect the eye from accidental intra-beam viewing.

AEL is the maximum Accessible Emission Limit of laser radiation permitted within a particular laser CLASS.
1. In a specified wavelength range
2. In a specified exposure time
3. through a specified aperture stop
4. at a specified distance
Once the AEL for a particular CLASS is exceeded then the next higher CLASS must be considered.

CLASS 2 means --Safe within normal use. Low power, only applies to visible lasers 400-700nm.
A CLASS 2 laser is considered safe because the blink reflex (0.25s) will limit the exposure.
Can be dangerous for intentional prolonged exposure.
CLASS 2 lasers typically have an AEL of 1mW for Continuous Wave.
Can be pulsed or Continuous Wave.

CLASS 2M Lasers that are safe during normal use, including unintentional short-term direct intrabeam viewing with the unaided naked eye.
As with CLASS1M this CLASS will have a relatively low irradiance but the MPE could be exceeded with the use of focusing optics such as binoculars or telescopes.
As with CLASS2 lasers they are restricted to the visible region of the spectrum "
~ from simple to read and understand "Short Course for Laser Users" see: https://www.tcd.ie/Physics/research/facilities/oal/laser-safety/Laser_Safety_TCD_short_course2.pdf

Hope that helps---beyond the above you should use goggle read, and gain some education on what you do not understand/comprehend about lasers is a good idea and come to LPF if you can not find any answer.
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Well-known member
Feb 23, 2020
You can increase the perceived brightness by picking colors more strongly seen by the human eye:

But if you already chose a green-like color, that's about as far as you can get


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Well-known member
Apr 2, 2009
what they ^^^said.
kinda feel like I got trolled..IF NOT--mybad.