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405nm Visibility






I would imagine it depends on how well you see 405, being so close to the bottom of the spectrum some people see it as violet and some as really dark purple or even gray.

My newly acquired eBay 405nm pens look dark purple to me, tested at 20mw and beam is not visible to me even in pitch black. My under 5mw 532nm looks much brighter.
 
i can see my 100mw beam very easy in the dark, at first it was kinda hard but i guess my eyes got used to the wavelength now.
 
405nm is not easy to see in the dark unless you have 400mW+ of it. For me atleast. I could see my 450mW 405nm laser fine but it had to be a very dark room and the beam had to be close to parallel with my eye.
 
I would have thought you need 500mW for a visible beam but I guess it depends on the person. Also once you get one that is 500mW or more be careful when first using it until you get a feel for how powerful it is, it can set stuff on fire. The one I have requires dim lighting for me to see a beam.

Alan
 
I thought too that even 100mw will not be much visible in dark but the beam is for sure visible if i shine in a dark room, looks dim a bit only.
 
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Rifter said:
I would imagine it depends on how well you see 405, being so close to the bottom of the spectrum some people see it as violet and some as really dark purple or even gray.

My newly acquired eBay 405nm pens look dark purple to me, tested at 20mw and beam is not visible to me even in pitch black. My under 5mw 532nm looks much brighter.
Click to expand...

Interesting, I was looking at the 405nm 100mw one just for the nice host:

HL 405,445,450nm
 
I'm just going to give you the data and let you work out the math yourself. At 650nm the sensitivity of the human eye is 0.107 of maximum. Peak sensitivity of 1.000 is at 555nm. At 532nm (common green laser pointer) it's 0.862. For 405nm there are conflicting figures. CIE 1931 says 0.00064 while CIE 1978 says 0.004656. I've heard that CIE 1978 works better for young adults in their early-to-mid twenties, while CIE 1931 works better for people in the 40-50 age range. There's also CIE 2006 which has figures for people age 20-80 in ten year increments, but their newer data is proprietary and costs money, so I haven't seen the numbers.

They say children can see 405nm ten times as well as adults, although I haven't seen that confirmed. Many middle-aged adults can't see color in a 405, just gray.

The way the eye works, apparent brightness is not directly proportional to intensity, but to the square root of intensity.

All this applies to the dot, but not necessarily to the beam. When the beam is seen "with smoke" that's the Tyndall effect. It follows the same brightness rules as the dot. "Without smoke" is Rayleigh scattering. The shorter the wavelength the more Rayleigh scattering you get. To calculate how much, divide 1 by the fourth exponent of the wavelength. The Rayleigh scattering with 405nm is 6.635 times as great as at 650nm.

Just off hand, I would agree with others here who say get a 500mW if you really want to see the beam. Just be careful with the dot, since at this wavelength you can't see how bright it really is. That means nothing indoors, and certainly no burning without eye protection. 405nm also presents a blue-light hazard, just basically bad for your eyes.

I know, you just want knock it out for the host, but in case you're wondering.
 
zyxwv99 said:
I'm just going to give you the data and let you work out the math yourself. At 650nm the sensitivity of the human eye is 0.107 of maximum. Peak sensitivity of 1.000 is at 555nm. At 532nm (common green laser pointer) it's 0.862. For 405nm there are conflicting figures. CIE 1931 says 0.00064 while CIE 1978 says 0.004656. I've heard that CIE 1978 works better for young adults in their early-to-mid twenties, while CIE 1931 works better for people in the 40-50 age range. There's also CIE 2006 which has figures for people age 20-80 in ten year increments, but their newer data is proprietary and costs money, so I haven't seen the numbers.

They say children can see 405nm ten times as well as adults, although I haven't seen that confirmed. Many middle-aged adults can't see color in a 405, just gray.

The way the eye works, apparent brightness is not directly proportional to intensity, but to the square root of intensity.

All this applies to the dot, but not necessarily to the beam. When the beam is seen "with smoke" that's the Tyndall effect. It follows the same brightness rules as the dot. "Without smoke" is Rayleigh scattering. The shorter the wavelength the more Rayleigh scattering you get. To calculate how much, divide 1 by the fourth exponent of the wavelength. The Rayleigh scattering with 405nm is 6.635 times as great as at 650nm.

Just off hand, I would agree with others here who say get a 500mW if you really want to see the beam. Just be careful with the dot, since at this wavelength you can't see how bright it really is. That means nothing indoors, and certainly no burning without eye protection. 405nm also presents a blue-light hazard, just basically bad for your eyes.

I know, you just want knock it out for the host, but in case you're wondering.
Click to expand...

Thanks for the lesson. I feel like I'm in school again LOL. Thankfully I still have two more months before I go back:)
 
If you have the 100mW 405nm focused on a match head and you have been drenched in kerosene then yes, it is dangerous to look at. Otherwise no.
 
My 405nm in a C11 is close to 700mW and is quite visible in the light of a room lit with incandescent or fluorescent light. The beam is a nice violet color and is quite powerful, being able to burn white paper at about a foot in distance.
 
As zyxwv99 mentioned Rayleigh scattering makes a laser beam visible.
It also seems that some people perceive UV better than others.
Dot shape & optics are no1 factors in beam forming.
In any case it seems that beam visibility is "subjective" and depends on many variables.

What i don't really comprehend is the eye's sensitivity to color, do colorblind people see the intensity of the light produced by the beam ? Maybe see white-silver beam like aging people's retina.

I will be doing some full spectrum photo tests, for personal use and info on color and light intensity. I will share of course, as sharing is in my nature.
 
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