Can violet lasers trick our eyes into seeing white?

[Daniel Petka]

Violet itself is weird, because it lays at the other side of the spectrum than red, yet it can be easily mimicked with red and blue. The more powerful the violet light, the more it resembles white.

My hypothesis: Violet tricks our eyes by activating not only blue, but also red and... with more power even green receptors.

(Please prove it wrong if its possible)

(Photo: middle white just like in reality (actually closer to cyan cause the wall is yellow, no idea why- pure observation- comment if you know y :p))

Observation: I've been playing with (not too powerful) lasers since I was a kid. One thing I noticed, was the unexpected color of the dot's center. It mostly seemed to be white- just like a camera picks it up. The red lasers couldn't achieve it, all I got from fairly powerful pointers (~100mW) was yellow in the middle. The green, however glowed clear white in the center of the dot.
There's more- the violet laser is not bright- even higher powers of 405nm can't outshine cheap green lasers. The dot though fairly change color with increasing power. That means violet laser dot looks kinda white; in a yellow environment almost cyan.

Thanks for reading this nonsense. ;)

I'll be happy if you prove my hypothesis wrong.

 

[A.T.]

My hypothesis: Violet tricks our eyes by activating not only blue, but also red and... with more power even green receptors.

Or the light converted to longer wave lengths by the wall.

 

[berkeman]

My hypothesis: Violet tricks our eyes by activating not only blue, but also red and... with more power even green receptors.

(Please prove it wrong if its possible)

Please remember that we do not allow personal speculation (although this is simple enough that it should be addressed fairly quickly). And it is not our job to prove you wrong -- that is not how the PF works.

 

[Daniel Petka]

Or the light converted to longer wave lengths by the wall.

Nope, the beam Looks violet too!

 

[A.T.]

Nope, the beam Looks violet too!

If the beam looks violet, while the diffuse reflection looks white, then eventually the spectrum changes on reflection.

 

[Daniel Petka]

If the beam looks violet, while the diffuse reflection looks white, then eventually the spectrum changes on reflection.

I guess I didn't express myself correctly.
The spectrum does NOT change through diffuse reflections. I checked it twice through a prism. It's still one single wavelength (405nm) that looks white when it's more powerful than usual.

 

[Daniel Petka]

Btw in your approach you forgot something: the beam is violet because it's simply less concentrated than the dot. That's the thing I've been talking about the whole time .

However you're not completely wrong. What you're talking about is fluorescence where high energy light (for example uv, or violet) gets converted to low energy light (green light)

 

[wukunlin]

It has to do with how our eyes work. The colours we see are signals from cone cells:
https://en.wikipedia.org/wiki/Cone_cell

Image sensors in cameras work similarly.
you can see that each absorption profile is a finite width, so your 405nm laser can actually trigger very small amounts of signal for your green and red (M and L) cone cells. If it is bright enough, all cells' signals are overloaded so you essential clip all the colour signals to the same strength, resulting in the perception of white colour.
Now for red lasers, you can also see that it really doesn't trigger much of any signal for the blue cone cell, probably the reason why you haven't been able to see a white centre.

 

[Daniel Petka]

Thanks wukunlin. I also had this picture in mind. Eventually it's maybe possible that the graph changes with increasing intensity.

 

[wukunlin]

Well, it's not really the absorption spectrum that is changing, but the output signal changed because they are hitting their respective maxima, and changing the frequency distribution