More Purple Than Blue

^^^^^I'm with oic0 on this one ^^^^^

LaserRX said:

As for why 405nm seems fuzzy, it's because the human eye can't focus on it properly. In fact our lens focuses the light slightly infront of our retina and not on it.

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The human eye possesses many more red and green cones per unit of area than blue cones (and probably more green than red). Because different wavelengths have slightly different focal lengths for the same simple lens (chromatic aberration), the eye is naturally calibrated to focus for detail in the wavelengths to which it is most sensitive and has the highest resolution, likely centered on 555nm.

This, of course, is at the expense of focussing blue. Moreover, since most of us tend towards myopia with age, blue focus (rather than deep red) is the first to go.

If you know someone with moderate to severe myopia (near-sightedness) worse than yours (but no astigmatism), borrow their glasses and watch things reverse: red will be fuzzier than green or blue.

Regarding perceived hue: I saw a comment somewhere that the difference between A130 and A140 diodes was wavelength -- that A130's were deeper blue at 445nm, while A140's were longer, more towards 450-455nm. Since longer means a brighter and purer blue, the A140's were binned for the more expensive model.

I don't recall who said that, but has anyone tried looking at these diodes with a spectrometer?

I see my A130 diode just as Tech Junkie does: pure blue dot, violet-ish bounce light (from non-fluorescing white surfaces). Fortunately, I just got a note from Jayrob that my order from him has been shipped, so with luck I'll be able to compare the output from my A130 and my new A140 build this weekend.

Would 5nm be that big difference ?

Canuke said:

Regarding perceived hue: I saw a comment somewhere that the difference between A130 and A140 diodes was wavelength -- that A130's were deeper blue at 445nm, while A140's were longer, more towards 450-455nm. Since longer means a brighter and purer blue, the A140's were binned for the more expensive model.

I don't recall who said that, but has anyone tried looking at these diodes with a spectrometer?

I see my A130 diode just as Tech Junkie does: pure blue dot, violet-ish bounce light (from non-fluorescing white surfaces). Fortunately, I just got a note from Jayrob that my order from him has been shipped, so with luck I'll be able to compare the output from my A130 and my new A140 build this weekend.

Click to expand...

I think what it really comes down to is how the individual classifies and defines "blue" and "purple" (I prefer the term "violet").

For clarity, when describing the 445nm light to others I use the term "indigo."

Pictures are not the most reliable way of determining the color, since by the time the picture makes it from the camera, to the monitor, the color will have changed.

Also, +/- 5nm is not that much of a difference. The human eye (and cameras for that matter) will have a tough time discerning a difference.

My sister has terrible eyes, when I had my arctic she said it looked like my blu ray. I then grabbed my blu ray and shined them side by side and she thinks the artic is the same color as my 6x. I see it as blue, but not quite as blue as 473nm. It's odd that the dot is bluer than the beam, could 445nm actually flouresce the air (or somehing similar)?

mikeeey said:

My sister has terrible eyes, when I had my arctic she said it looked like my blu ray. I then grabbed my blu ray and shined them side by side and she thinks the artic is the same color as my 6x. I see it as blue, but not quite as blue as 473nm. It's odd that the dot is bluer than the beam, could 445nm actually flouresce the air (or somehing similar)?

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Fluorescence will (almost) always excite the atoms to emit a photon of a longer wavelength, so it is not likely.

I can confirm that what others are saying and what you are saying here...
Low intensity 445nm light (the beam and diffuse reflection) is much closer to violet than the high intensity "spot."

I have here a 150mW 445 and at lower power, the color is definitely blue-violet (again, I call it indigo).

The difference is clear between 170mW 405nm, 150mW 445nm, and 160mW 473nm.

RA_pierce said:

I think what it really comes down to is how the individual classifies and defines "blue" and "purple" (I prefer the term "violet").

For clarity, when describing the 445nm light to others I use the term "indigo."

Pictures are not the most reliable way of determining the color, since by the time the picture makes it from the camera, to the monitor, the color will have changed.

Also, +/- 5nm is not that much of a difference. The human eye (and cameras for that matter) will have a tough time discerning a difference.

Click to expand...

I think that how an individual classifies color is just one of several variables. The fact that you make the distinction of the "indigo" hue, to me reflects that you are a photographer or you otherwise deal with color more than most. This is the case with me, as I am very visually-oriented and can discern hue variations with considerable precision. I work in the visual effects business, and so I'm dealing with light and color on a daily basis.

However, human eyes are known to vary in their sensitivity to different wavelengths, and the center wavelength for each of the three cones can also vary (to the point where two of them start to overlap and the person becomes a color-blind dichromat).

For me, 5nm can make a huge difference in certain areas -- when we are speaking about the 480nm area, where blue just begins to edge into turquoise. The color change from 505nm to 488nm to my eye is quite large. When the batteries die in my A130 build and the laser peters out, I can see its hue shift from 445nm to 470nm or so as it stops lasing. To me, 505nm is just flat-out green -- but in discussions on CPF, I have found that there is an unusually significant variation among what hue people see in that range.

Also, given the logarithmic response of the human eye, which gives us greater sensitivity to variations at low levels, I would expect us to be better at detecting subtle hue variations in dim lighting more so than bright -- hence the dot appearing blue while the bounce light drifts to violet-ish. This is consistent with my experience with bright violet sources as appearing more bluish, but their light becoming deep purple as it falls off.

There is a subtle "hump" in sensitivity for the long-wavelength (red) cones around 450nm and shorter, which gives the perceived violet hue in that area for most of us. I wouldn't be surprised to discover that some folks lack this hump, and as a result see only blue all the way out to 405nm and beyond.

I've found with the 445 the apparent color of the beam seems to depend a bit on the color of the ambient light.

The dot appears deep blue to me on non-fluorescent surfaces. On white paper and other somewhat fluorescent surfaces it looks blue too, but less saturated, a bit like what some overly-pimped-to-blue HID headlights produce.

Dot = very blue
Beam = very blue
Diffuse light = very blue with a slight hint of violet.

Canuke said:

The human eye possesses many more red and green cones per unit of area than blue cones (and probably more green than red). Because different wavelengths have slightly different focal lengths for the same simple lens (chromatic aberration), the eye is naturally calibrated to focus for detail in the wavelengths to which it is most sensitive and has the highest resolution, likely centered on 555nm.

This, of course, is at the expense of focussing blue. Moreover, since most of us tend towards myopia with age, blue focus (rather than deep red) is the first to go.

If you know someone with moderate to severe myopia (near-sightedness) worse than yours (but no astigmatism), borrow their glasses and watch things reverse: red will be fuzzier than green or blue.

Click to expand...

Thanks for taking the time to add the extra. This is also the reason people can only look at the "dot"s of these lasers for a short time before they feel dizzy or get a headache, in effect you are looking at something that is in a constant state of non-focus (due to the reasons you have nicely explained).

What I love about 405nm and in some cases 445nm is that these wavelengths cause many things to flouresce brightly. Great fun for pictures.

It's pure blue to my eyes. 405nm is very much violet though.

• 
• 50mW 420nm Purple Beam laser Pointer

I wonder if this laser is actually 420nm's

phoenix77 said:

• 
• 50mW 420nm Purple Beam laser Pointer

I wonder if this laser is actually 420nm's

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What does this have to do with anything that we are talking about? We are talking about 445nm lasers, not 420nm. But I can see why you like the 420. Its just not the place to talk about it. Drugs and lasers dont mix.

Why do you care anyway ? My question was not directed toward you:na:

'Cause you are, and continuing to throw the thread off topic. WTF you have been here over 2 years. You'd think you'd know better.