Comparison of brightness of light spot and beam among lasers of different wavelengths

Some beginners often ask me how much the power of 532nm laser equivalent to the brightness of 445nm laser is

The question may not be so easy to answer, because the sensitive degree of each eye to light of different wavelengths is not the same.
And the feelings will be also different in the dark and light conditions .
Scientists have established light / dark vision functions respectively according to the mean value of human vision in the light / dark environments.
When the brightness is more than 3cd/㎡, it is a photopic vision, and pyramidal cells play a major role, peak value of V（λ）will be between 550nm~560nm; when the brightness is less than 0.03cd/㎡, it is a scotopic vision, rod cells play a major role, peak value of V（λ）shifts to short wavelength, equivalent to blue green parts between 500~510nm. Functions with brightness between 3~0.03 also appear in this position.

First let’s discuss the spot brightness. Spot brightness is basically decided by visual function when the power and density are the same.
The function value of 532nm is very high both in light and dark conditions, so it has relatively high brightness.
While the function value of 445nm is quite different in light and dark conditions, theoretically, the brightness is very low in daytime and has a good effect in night.
But, in fact, we also need to consider the factor of the main light.

For example, observe spots in the sunlight.

This is the power distribution of sun light.

Spot brightness also depends on the difference value of light source.
Just like 445nm, it is in a depressed position of solar spectrum, so it has a obvious contrast that the brightness of observation under sunlight has improved.
Next, let’s talk about the beam brightness.
Beam brightness is not only related with vision function but also has a great relationship with the scattering rate.

Even when they have the same power and beam diameter, because the air scattering rate is not the same, their power density will be different.
Atmospheric scattering is divided into various types, some have a stronger scattering to short wave, while some have basically the same scattering to full waves.
So this has enhanced beam brightness of short wave like 445nm once again, but it has also increased the loss of distant 445nm beam, therefore, 445nm beam often looks bright up close and dark at a distance.

Finally, I would like to remind of the safety of yourselves and others.

Ensure that there is no any personnel near light path or new light path that may be generated by reflection.
We are not recommending to observe laser spot up close with naked eyes without any protection.