I'm a researcher at University Federal of Santa Catarina Brazil and I work with lasers.

I'm looking for information about how to calculate the Nominal Ocular Hazard Distance (NOHD) to a laser line and not to a laser point.

I have a laser line with 150 mW, thickness 1,14 mm with working distance 5m and fan angle 30°. Link

I would like to know the Nominal Ocular Hazard Distance (NOHD) with application to this laser line.

  • 1
    $\begingroup$ NOHD is not a physics concept. $\endgroup$
    – G. Smith
    Oct 16, 2020 at 2:51
  • $\begingroup$ @G.Smith thanks for the excellent contribution, helped a lot, keep the hard work! $\endgroup$
    – Pedro77
    Oct 19, 2020 at 18:12
  • $\begingroup$ @Pedro77 The Code of Conduct here says “Avoid sarcasm”. $\endgroup$
    – G. Smith
    Oct 19, 2020 at 18:56

1 Answer 1


Assuming this is a CW laser operating between 400nm-700nm:

$E$ (our irradiance) is taken to be the MPE (maximum permissible exposure) of a Class 2 laser: $1.8T^{-0.25} \times 10^{-3} \text{ watts/cm}^2$

Our NOHD will be:

$$D_{\text{NOHD}}=\frac{\phi}{w\times\theta\frac{\pi}{180}\times1.8T^{-0.25} \times 10^{-3} \text{ W/cm}^2}$$

where $w$ is our beam width (should be 7mm for lasers with a beam width less than 0.7mm), $\theta$ is our fan angle, and $\phi$ is our radiant power.

Plugging in our values and making $T$ a 'blink': $$D_{\text{NOHD}}=\frac{150\times10^{-3}\text{ W}}{0.7\text{ cm}\times 30^{\circ} \frac{\pi}{180}\times1.8\times0.25^{-0.25} \times 10^{-3} \text{ W/cm}^2}=160\text{ cm}$$

You have posted too little information really. What kind of laser is it? Wavelength? CW? Pulsed? Class?

  • $\begingroup$ The streamline that I have is a laser diode with 640 nm, CW and Class 3B. Could you send me any reference to study about this calculation? So glad for your help $\endgroup$ Oct 16, 2020 at 14:21
  • $\begingroup$ Thanks for your help. This information it's very important for me. If you have any document to help me learn more, I'll be very happy. $\endgroup$ Oct 19, 2020 at 19:40

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