I haven't posted in a while, but this topic is relevant to a purchase decision I was trying to make. I was on the
Sanwu Lasers Challenger II page and was trying to chose between getting 470nm@4W or 520nm@1W. I ended up getting the 470nm@4W laser, as I was going to use the laser mostly at night and I knew that our sensitivity shifted a bit to the shorter wavelengths in low light. I figured the blue one would appear brighter. However, according to the
calculator, it's still only 77% as bright compared to the green. You said it's "too harsh on blue power," does that mean the blue might have a higher percentage in comparison?
What Steve001 And Alaskan have said above +
yes, 1W 520nm is brighter, easier on the eyes, and safer( only 1W dangerous but still dangerous for eyes)
Dot is only 1/2 as bright and beam 77% according to the calculator
You are not going to notice the beam brightness difference very much in a side by side test and the blue is 4X as powerful if you need that output power for anything like burnng power.
Whatever you do be safe wear laser goggles and use safe laser operationand handiling procedures--- 4W can end you eyesight quicker than the blink refles of an eye of 0.25 seconds --there is no chance to correct once an accident is in progress--goggles are they only way.
How bright the beam is depends very much on atomspheric conditions .
It depends on the many factors of air where you are at any given point in time.
Laser beam visibility is highly dependent on ever changing atmospheric conditions and aerosols in the air.
You never actually see the laser beam --what you see is the reflections from particles in the air. No matter what output power 100 mW or 100W or wavelength/color there is no visible laser beam in a vacuum.
At sea-level, one cubic inch (1 inch x 1 inch x 1 inch) (16.39 cm3) of "air" contains approximately 400 billion billion (4*1020) air molecules, each moving at about 1600 km/hr (1000 miles/hr), and colliding with other molecules and anything else they come into contact with about 5 billion times per second. This is the reason for "air pressure". The amount of particles in that air that can reflect a portion of a laser beam's light back to your eye determines if you can see it or not.
It all depends upon atmospheric conditions--a beam you can see extremely well in fog or area with high concentration of particulate matter in the air can be almost invisible in clean clear air
"In a vacuum, the laser beam itself would be invisible - regardless of power or color. As a laser beam passes through Earth's Atmosphere some of the photons encounter large airborne particles which reflect some of the light back to an observer. This only creates intermittent tiny bright flashes of light or "knots" in the beam - it is not why we can see the beam itself.
It is extremely small airborne particles called aerosols having a diameter significantly less than the wavelength of the light that causes the beam to become visible.
The effect of minute particles scattering light is called Rayleigh scattering and it's most noticeable effect is to turn the daytime sky blue. Rayleigh scattering causes photons to be scattered in a roughly spherical manner around these particles. Some of the light is scattered forward (in the direction of the beam), a lesser amount is scattered to the sides and about the same amount that is scattered forward is scattered backwards towards the light source. This backwards scattering is why the beam is more visible to people standing near the astronomer using it, than people standing some distance to the side. The more of these minute particles there are in the atmosphere, the more Rayleigh scattering there is."
From :
RASC Calgary Centre - The Atmosphere, Astronomy and Green Lasers
Really you need to understand aerosols in air --is very interesting actually--you need to know what they are locally and density of same to be able to figure laser beam visibility possibilities of one place compared to another place on the earths surface. Example: the most aerosol-laden air in the United States today pales in comparison to Asia. So laser beams are more visible there, generally speaking. Depending on the season and weather conditions, surges of aerosols can make their way into the atmosphere almost anywhere on Earth
See NASA Earth Observatory page for an excellent explaination of aerosols in air with lots of pictures and charts of the planetary distribution of aerosols.
See:
https://earthobservatory.nasa.gov/Features/Aerosols/
Probably more answer than you wanted --hope it helps you understand the nature of laers beam visibility.