Laser Pointer Safe to use with fish?

[Ann R]

Is it safe to use a red laser pointer for the tank? I'm getting tired of
saying to hubby "See the shrimp? Ok - see the knob next to him.. Now go
straight over to the little hole in the rock and down about an inch..." It
would be much easier to use the pointer but I don't want to disturb the
critters.

--
Ann R

[CheezWiz]

The glass and salt water of the tank should render a laser pointer harmless.
It would take quite a bit of staring into the beam to cause any damage to
the rods and cones of any creature.
At the low power put out by publicly available laser pointers, most are very
safe in that respect..
Modified output models are a different story.. (green + Ebay)

I love using mine to play with my female clown, she is very diligent to
chase the red dot off of her anemone and around the tank..!

CW

"Ann R" > wrote in message
news:Ymdee.18264$KP.13938@trndny02...
> Is it safe to use a red laser pointer for the tank? I'm getting tired of
> saying to hubby "See the shrimp? Ok - see the knob next to him.. Now go
> straight over to the little hole in the rock and down about an inch..."
> It would be much easier to use the pointer but I don't want to disturb the
> critters.
>
> --
> Ann R
>

[Ann R]

Guess what hubby's getting for mother's day!

--
Ann R
"CheezWiz" > wrote in message
...
> The glass and salt water of the tank should render a laser pointer
> harmless.
> It would take quite a bit of staring into the beam to cause any damage to
> the rods and cones of any creature.
> At the low power put out by publicly available laser pointers, most are
> very safe in that respect..
> Modified output models are a different story.. (green + Ebay)
>
> I love using mine to play with my female clown, she is very diligent to
> chase the red dot off of her anemone and around the tank..!
>
> CW
>
> "Ann R" > wrote in message
> news:Ymdee.18264$KP.13938@trndny02...
>> Is it safe to use a red laser pointer for the tank? I'm getting tired of
>> saying to hubby "See the shrimp? Ok - see the knob next to him.. Now go
>> straight over to the little hole in the rock and down about an inch..."
>> It would be much easier to use the pointer but I don't want to disturb
>> the critters.
>>
>> --
>> Ann R
>>
>
>

[George]

"CheezWiz" > wrote in message
...
> The glass and salt water of the tank should render a laser pointer harmless.
> It would take quite a bit of staring into the beam to cause any damage to the
> rods and cones of any creature.
> At the low power put out by publicly available laser pointers, most are very
> safe in that respect..
> Modified output models are a different story.. (green + Ebay)
>
> I love using mine to play with my female clown, she is very diligent to chase
> the red dot off of her anemone and around the tank..!
>
> CW

Most oceanic fish cannot see red light very well, if at all, anyway. Red light
doesn't penetrate the ocean very far down, which is why it always looks deep
blue in diving photos (actinic blue light is needed for sal****er aquariums
because that wavelength penetrates the deepest in water, and so most creatures
in the sea that need sunlight need this wavelength). Think about it. A maroon
clown fish is red because red makes for great camoflage. And the vertical white
stripes confuses predators because the fish is usually found in an anemone.

> "Ann R" > wrote in message
> news:Ymdee.18264$KP.13938@trndny02...
>> Is it safe to use a red laser pointer for the tank? I'm getting tired of
>> saying to hubby "See the shrimp? Ok - see the knob next to him.. Now go
>> straight over to the little hole in the rock and down about an inch..." It
>> would be much easier to use the pointer but I don't want to disturb the
>> critters.
>>
>> --
>> Ann R
>>
>
>

[George]

"Ann R" > wrote in message
news:%veee.15442$yd1.4490@trndny01...
> Guess what hubby's getting for mother's day!
>
> --
> Ann R
> "CheezWiz" > wrote in message
> ...
>> The glass and salt water of the tank should render a laser pointer harmless.
>> It would take quite a bit of staring into the beam to cause any damage to the
>> rods and cones of any creature.
>> At the low power put out by publicly available laser pointers, most are very
>> safe in that respect..
>> Modified output models are a different story.. (green + Ebay)
>>
>> I love using mine to play with my female clown, she is very diligent to chase
>> the red dot off of her anemone and around the tank..!
>>
>> CW

Most likely, she sees the dot as a black spot.

>> "Ann R" > wrote in message
>> news:Ymdee.18264$KP.13938@trndny02...
>>> Is it safe to use a red laser pointer for the tank? I'm getting tired of
>>> saying to hubby "See the shrimp? Ok - see the knob next to him.. Now go
>>> straight over to the little hole in the rock and down about an inch..." It
>>> would be much easier to use the pointer but I don't want to disturb the
>>> critters.
>>>
>>> --
>>> Ann R
>>>
>>
>>
>
>

[Mislav]

> Most oceanic fish cannot see red light very well, if at all, anyway. Red
> light
> doesn't penetrate the ocean very far down, which is why it always looks
> deep blue in diving photos (actinic blue light is needed for sal****er
> aquariums because that wavelength penetrates the deepest in water, and so
> most creatures in the sea that need sunlight need this wavelength). Think
> about it. A maroon clown fish is red because red makes for great
> camoflage. And the vertical white stripes confuses predators because the
> fish is usually found in an anemone.
>
If this was true why are there black fish? Why aren't they all red? Why my
sailfin tang chases the red dot produced by laser pointer?

[Happy'Cam'per]

"Mislav" > wrote in message ...
>
> >
> If this was true why are there black fish? Why aren't they all red? Why my
> sailfin tang chases the red dot produced by laser pointer?

It is 100% true, no doubt about it. You have to remember that we see our
fish in less than 1 meter of water, while in the ocean depths the fish's
colouring will be drastically different from what we see in our tanks. Fish
also see colour different from what we see. There was a brilliant link
floating round here some months ago about this very topic, it was focusing
on the way Mantis Shrimp perceive colours. Very interesting, perhaps someone
still has the link.
--
Kind Regards
Cameron

[Charles Spitzer]

"Happy'Cam'per" > wrote in message
...
> "Mislav" > wrote in message ...
>>
>> >
>> If this was true why are there black fish? Why aren't they all red? Why
>> my
>> sailfin tang chases the red dot produced by laser pointer?
>
> It is 100% true, no doubt about it. You have to remember that we see our
> fish in less than 1 meter of water, while in the ocean depths the fish's
> colouring will be drastically different from what we see in our tanks.
> Fish
> also see colour different from what we see. There was a brilliant link
> floating round here some months ago about this very topic, it was focusing
> on the way Mantis Shrimp perceive colours. Very interesting, perhaps
> someone
> still has the link.
> --
> Kind Regards
> Cameron

the most recent national geographic magazine has a good article on this.
they've discovered that fish can see different wavelengths than us (mostly
uv), and what looks dark or muted at low depths is different to fish eyes.
they also said that mantis shrimp have 18 different mechanisms to see colors
that humans can't, and that humans have only 4. the article showed pictures
of what brilliantly colored fish really look like to other fish.

http://magma.nationalgeographic.com/ngm/0505/feature5/index.html
http://magma.nationalgeographic.com/ngm/0505/sights_n_sounds/index.html

regards,
charlie
cave creek, az

[George]

"Mislav" > wrote in message ...
>
>> Most oceanic fish cannot see red light very well, if at all, anyway. Red
>> light
>> doesn't penetrate the ocean very far down, which is why it always looks deep
>> blue in diving photos (actinic blue light is needed for sal****er aquariums
>> because that wavelength penetrates the deepest in water, and so most
>> creatures in the sea that need sunlight need this wavelength). Think about
>> it. A maroon clown fish is red because red makes for great camoflage. And
>> the vertical white stripes confuses predators because the fish is usually
>> found in an anemone.
>>
> If this was true why are there black fish? Why aren't they all red? Why my
> sailfin tang chases the red dot produced by laser pointer?

Because black fish are even harder to see, especially at depth. Regardless, it
is a fact that red light barely penetrates the ocean's depths. It is also a
fact that many fish cannot see the color red. As for why your sailfin tang
chases the red dot, I cannot say anything about Sailfin Tang psychology, but it
is likely that the fish is seeing the red dot as a black dot. It is also likely
that since these fish are territorial, that it sees the erratically moving
red/black dot as some sort of threat.

[CheezWiz]

Only problem with this is that lasers by definition are monochromatic.
They only produce a single wavelength of light. In the case of red, about
632 nm.

So if the fish can see it to chase it, then it is detecting the wavelength
of that laser.
How the fish perceives the dot may be black for all we know, but if it
detects a monochromatic light source that is red, then it sees red..

"George" > wrote in message
news:lHAee.59023$WI3.3170@attbi_s71...
>
> "Mislav" > wrote in message ...
>>
>>> Most oceanic fish cannot see red light very well, if at all, anyway. Red
>>> light
>>> doesn't penetrate the ocean very far down, which is why it always looks
>>> deep blue in diving photos (actinic blue light is needed for sal****er
>>> aquariums because that wavelength penetrates the deepest in water, and
>>> so most creatures in the sea that need sunlight need this wavelength).
>>> Think about it. A maroon clown fish is red because red makes for great
>>> camoflage. And the vertical white stripes confuses predators because
>>> the fish is usually found in an anemone.
>>>
>> If this was true why are there black fish? Why aren't they all red? Why
>> my sailfin tang chases the red dot produced by laser pointer?
>
> Because black fish are even harder to see, especially at depth.
> Regardless, it is a fact that red light barely penetrates the ocean's
> depths. It is also a fact that many fish cannot see the color red. As
> for why your sailfin tang chases the red dot, I cannot say anything about
> Sailfin Tang psychology, but it is likely that the fish is seeing the red
> dot as a black dot. It is also likely that since these fish are
> territorial, that it sees the erratically moving red/black dot as some
> sort of threat.
>

[Happy'Cam'per]

"Charles Spitzer" > wrote in message

> they've discovered that fish can see different wavelengths than us (mostly
> uv), and what looks dark or muted at low depths is different to fish eyes.

This is slightly off topic but Moths and Butterflies also see colour in UV.
If you ever thought that Moths only came in greys and browns you would be
very wrong. If you take a small handheld uv lamp, the kind they use to make
uv ink visible, and shine it on a moth at night you will see all sorts of
freaky colours, truly amazing.
--
Kind Regards
Cameron

[George]

"CheezWiz" > wrote in message
...
> Only problem with this is that lasers by definition are monochromatic.
> They only produce a single wavelength of light. In the case of red, about 632
> nm.
>
> So if the fish can see it to chase it, then it is detecting the wavelength of
> that laser.
> How the fish perceives the dot may be black for all we know, but if it detects
> a monochromatic light source that is red, then it sees red..

http://ebiomedia.com/gall/eyes/underwater.html

"Water not only reduces the amount of light that penetrates a fish's world but
also the kind of light. The extinction of sunlight in the water column happens
very fast. On average, 90% of the light is gone by 10m depth, and 99% by 40m.
Varying wavelengths of light are absorbed at different depths. UV light is
eliminated in the first few millimeters of water; infrared in the first few
centimeters. Of the wavelengths of visible light, the red wavelengths disappear
in the first 5m or so, then the yellows. Eventually, at a depth of around 100m,
all that remains is a narrow band of blue-green wavelengths (510nm-540nm).
There is complete darkness below about 200 meters. It makes good sense that fish
eyes have maximum sensitivity for blue light (at about 520nm wavelength).
Fish visual pigments, called rhodopsins, are photosensitive protein pigments
found in the rod cells of the retina. When light passes into the eye and reaches
the retina, rhodopsin protein molecules become photo-excited. Biochemical
changes in the structure of the molecule cause electrical impulses to run down
the optic nerve sending information to the brain.

Rhodopsins, which are also found in all other vertebrate animals, are a dark
reddish color. Like deep growing red algae, the rhodopsin pigment absorb the
only wavelengths that penetrate the water column: greens and blues. Therefore,
the rhodopsin, like the algae, reflects the light it does not absorb - which is
generally the red wavelengths of light, causing its reddish color. Our own human
rhodopsins are still red, a heirloom of our aquatic ancestry."

With the fish in question, if it evolved in a shallow water environment (5m or
less), theoretically, it is possible that it could have a slight adaptation for
seeing red. Having said that, it is more likely to see it as a shade (probably
gray or black) other than red due to the tendency of rhodopsins not to absorb
red wavelengths. So what it is more likely responding to is not the color
itself, but the movement (of something that to it appears like a shadow) of the
lazer dot as it is moved around in the aquarium.

I hope this answers your question.

[George]

"George" > wrote in message
news:U6Fee.59609$c24.22151@attbi_s72...
>
> "CheezWiz" > wrote in message
> ...
>> Only problem with this is that lasers by definition are monochromatic.
>> They only produce a single wavelength of light. In the case of red, about 632
>> nm.
>>
>> So if the fish can see it to chase it, then it is detecting the wavelength of
>> that laser.
>> How the fish perceives the dot may be black for all we know, but if it
>> detects a monochromatic light source that is red, then it sees red..
>
> http://ebiomedia.com/gall/eyes/underwater.html
>
> "Water not only reduces the amount of light that penetrates a fish's world but
> also the kind of light. The extinction of sunlight in the water column happens
> very fast. On average, 90% of the light is gone by 10m depth, and 99% by 40m.
> Varying wavelengths of light are absorbed at different depths. UV light is
> eliminated in the first few millimeters of water; infrared in the first few
> centimeters. Of the wavelengths of visible light, the red wavelengths
> disappear in the first 5m or so, then the yellows. Eventually, at a depth of
> around 100m, all that remains is a narrow band of blue-green wavelengths
> (510nm-540nm). There is complete darkness below about 200 meters. It makes
> good sense that fish eyes have maximum sensitivity for blue light (at about
> 520nm wavelength).
> Fish visual pigments, called rhodopsins, are photosensitive protein pigments
> found in the rod cells of the retina. When light passes into the eye and
> reaches the retina, rhodopsin protein molecules become photo-excited.
> Biochemical changes in the structure of the molecule cause electrical impulses
> to run down the optic nerve sending information to the brain.
>
> Rhodopsins, which are also found in all other vertebrate animals, are a dark
> reddish color. Like deep growing red algae, the rhodopsin pigment absorb the
> only wavelengths that penetrate the water column: greens and blues. Therefore,
> the rhodopsin, like the algae, reflects the light it does not absorb - which
> is generally the red wavelengths of light, causing its reddish color. Our own
> human rhodopsins are still red, a heirloom of our aquatic ancestry."
>
> With the fish in question, if it evolved in a shallow water environment (5m or
> less), theoretically, it is possible that it could have a slight adaptation
> for seeing red. Having said that, it is more likely to see it as a shade
> (probably gray or black) other than red due to the tendency of rhodopsins not
> to absorb red wavelengths. So what it is more likely responding to is not the
> color itself, but the movement (of something that to it appears like a shadow)
> of the lazer dot as it is moved around in the aquarium.
>
> I hope this answers your question.
>

I might also note that the 632 nm for your laser that you refer to is at the low
end for red, and actually verges on orange, which starts at about 625 nm. We
might see it as red since our eyes are more sensitive to red. It is not to
likely that the fish sees it as red, since their eyes are not sensitive to it.

[Mislav]

In most part I agree with you that red color doesn't penetrate deep into
water. But I don't agree that fish cannot see red color. As CheezWiz said
laser produces a single wavelength of light about 632 nm for red light.
Why do percula clowns have transition between red and white with black line?
Surely it isn't just esthetics, it must have some evolutionary reason. It
seams that other fish must see it, otherwise it wouldn't develop black
color.

>>So what it is more likely responding to is not the color itself, but the
>>movement (of something that to it appears like a shadow) of the lazer dot
>>as it is moved around in the aquarium.

My sailfin chases the dot trying to eat it. He perecieves it as a food. If
he sees that something is moving he must see the red color of laser pointer
'cose it is only single wavelength.

Mislav

[George]

"Mislav" > wrote in message ...
> In most part I agree with you that red color doesn't penetrate deep into
> water. But I don't agree that fish cannot see red color. As CheezWiz said
> laser produces a single wavelength of light about 632 nm for red light.
> Why do percula clowns have transition between red and white with black line?
> Surely it isn't just esthetics, it must have some evolutionary reason. It
> seams that other fish must see it, otherwise it wouldn't develop black color.

It is for camouflage. Like I said in a previous post, "Rhodopsins, which are
also found in all other vertebrate animals, are a dark reddish color. Like deep
growing red algae, the rhodopsin pigment absorb the only wavelengths that
penetrate the water column: greens and blues. Therefore,
the rhodopsin, like the algae, reflects the light it does not absorb - which is
generally the red wavelengths of light. 632nm is nearly orange (625nm). Our
eyes are more sensitive to red, so we see the lazer light as red, not as
orangish red. I know all of this is hard to understand, but one look at how
certain fish look in UV gives you a much better understanding of how fish
actually see each other and the world around them.

>>>So what it is more likely responding to is not the color itself, but the
>>>movement (of something that to it appears like a shadow) of the lazer dot as
>>>it is moved around in the aquarium.
>
> My sailfin chases the dot trying to eat it. He perecieves it as a food. If he
> sees that something is moving he must see the red color of laser pointer 'cose
> it is only single wavelength.
>
> Mislav
>

Fish are territorial. A bass will strike at a lure passing close by more often
out of defensive behavior than out of hunger. And they could really care less
what color it is. The color is more for the lure owner than the fish. Fish
have rods (for black and white) and cones (for color) like we do. Because the
rhodopsin generally do not absorb red light, what your fish is probably seeing
is grayscale, like a shadow flittering around in the tank. It sees this strange
gray/black "thing", this dot scurrying about in its territory and it chases it,
just like a bass will strike a lure that gets thrown into its territory.

[CheezWiz]

> I might also note that the 632 nm for your laser that you refer to is at
> the low end for red, and actually verges on orange, which starts at about
> 625 nm. We might see it as red since our eyes are more sensitive to red.
> It is not to likely that the fish sees it as red, since their eyes are not
> sensitive to it.

I think you are still trying to mix RECEPTION with PERCEPTION.

There is no biological mechanism to receive "Orange" wavelengths.
If a fish even detects that a 632 nm laser is there, then it must have red
cones in its eye.
Unless its green cones can see all the way up to the red spectrum of the
chart.

Orange would be a mix of Red and Green wavelengths, but a laser is
MONOCHROMATIC.
A fish without a cone that can detect that frequency will see no light and
no shadow from a red laser pointer.

http://www.cartage.org.lb/en/themes/Sciences/Zoology/AnimalPhysiology/SensoryReception/SensoryReception.htm
"How do fish see?
The optical system in fish is very similar to that of the land vertebrates,
however, there are some important differences. The fish has a more spherical
shaped lens than the land dwellers. Fish focus by changing the relative
distance between the lens and the retina, where as other vertebrates change
the curvature of their more flexible lens. Fish have choroids which contain
a special structure, the tapetum lucidum, and this contains very reflective
guanine crystals to aid in dim light vision. This is very important because
of the lowered amount of light that penetrates the fish's watery
environment. Additionally, many deep-sea fish have only these and rods, for
increased low light sensitivity. They even have epithelial layers for the
specific purpose of protection from bright light.

Fish with cones generally have four types, red, green, blue, and
ultraviolet. Some only have two or three of these possibilities; fish with
all four usually live close to the water's surface, and may have further
special adaptations. Some fish have upwardly directed eyes, especially those
who are preyed upon by birds. Some deep sea fishes have tubular eyes, which
help to concentrate the limited light that penetrates to great depths. The
South American "four-eyed fish " swims along the surface, with it's eyes
protruding partly out of the water. Each of its two eyes is split into an
upper half for vision in the air and a lower half for underwater vision."

Since rods only detect luminosity in the blue and green wavelengths of the
Electro Magnetic Spectrum, I find it hard to believe that a fish with no red
sensing cones could detect a red laser pointer. Also, most red diode lasers
are 635nm and up in wavelength. 632nm is for a helium-neon laser
specifically.
http://www.lexellaser.com/techinfo_wavelengths.htm

I would guess that most reef fish have red cones in their eyes....

CW
"George" > wrote in message
news:phFee.59534$WI3.14130@attbi_s71...
>
> "George" > wrote in message
> news:U6Fee.59609$c24.22151@attbi_s72...
>>
>> "CheezWiz" > wrote in message
>> ...
>>> Only problem with this is that lasers by definition are monochromatic.
>>> They only produce a single wavelength of light. In the case of red,
>>> about 632 nm.
>>>
>>> So if the fish can see it to chase it, then it is detecting the
>>> wavelength of that laser.
>>> How the fish perceives the dot may be black for all we know, but if it
>>> detects a monochromatic light source that is red, then it sees red..
>>
>> http://ebiomedia.com/gall/eyes/underwater.html
>>
>> "Water not only reduces the amount of light that penetrates a fish's
>> world but also the kind of light. The extinction of sunlight in the water
>> column happens very fast. On average, 90% of the light is gone by 10m
>> depth, and 99% by 40m. Varying wavelengths of light are absorbed at
>> different depths. UV light is eliminated in the first few millimeters of
>> water; infrared in the first few centimeters. Of the wavelengths of
>> visible light, the red wavelengths disappear in the first 5m or so, then
>> the yellows. Eventually, at a depth of around 100m, all that remains is a
>> narrow band of blue-green wavelengths (510nm-540nm). There is complete
>> darkness below about 200 meters. It makes good sense that fish eyes have
>> maximum sensitivity for blue light (at about 520nm wavelength).
>> Fish visual pigments, called rhodopsins, are photosensitive protein
>> pigments found in the rod cells of the retina. When light passes into the
>> eye and reaches the retina, rhodopsin protein molecules become
>> photo-excited. Biochemical changes in the structure of the molecule cause
>> electrical impulses to run down the optic nerve sending information to
>> the brain.
>>
>> Rhodopsins, which are also found in all other vertebrate animals, are a
>> dark reddish color. Like deep growing red algae, the rhodopsin pigment
>> absorb the only wavelengths that penetrate the water column: greens and
>> blues. Therefore, the rhodopsin, like the algae, reflects the light it
>> does not absorb - which is generally the red wavelengths of light,
>> causing its reddish color. Our own human rhodopsins are still red, a
>> heirloom of our aquatic ancestry."
>>
>> With the fish in question, if it evolved in a shallow water environment
>> (5m or less), theoretically, it is possible that it could have a slight
>> adaptation for seeing red. Having said that, it is more likely to see it
>> as a shade (probably gray or black) other than red due to the tendency of
>> rhodopsins not to absorb red wavelengths. So what it is more likely
>> responding to is not the color itself, but the movement (of something
>> that to it appears like a shadow) of the lazer dot as it is moved around
>> in the aquarium.
>>
>> I hope this answers your question.
>>
>
> I might also note that the 632 nm for your laser that you refer to is at
> the low end for red, and actually verges on orange, which starts at about
> 625 nm. We might see it as red since our eyes are more sensitive to red.
> It is not to likely that the fish sees it as red, since their eyes are not
> sensitive to it.
>

[CheezWiz]

"
Safety.

Care should always be taken, especially with children, when using a laser
pointer. Exposure to a couple of seconds of the laser beam will cause only
temporary "spots" in front of the eyes. Even small children do not focus on
the sun because it is uncomfortable and the same is true of the laser
pointer beam. But the power is great enough to damage the eye if someone
stares directly at it long enough. Of the millions of pointers sold, the FDA
knows of only 2 cases which have caused serious eye injury and none have
resulted in permanent blindness. In these two cases, the victim stared
directly at the beam for 10 seconds or more. Insurance companies are perhaps
the best gauge of danger, since their financial well-being depends on
identifying dangerous products. The premium for laser pointer insurance is
no more than for office chairs.
"





"Ann R" > wrote in message
news:Ymdee.18264$KP.13938@trndny02...
> Is it safe to use a red laser pointer for the tank? I'm getting tired of
> saying to hubby "See the shrimp? Ok - see the knob next to him.. Now go
> straight over to the little hole in the rock and down about an inch..."
> It would be much easier to use the pointer but I don't want to disturb the
> critters.
>
> --
> Ann R
>

[Rocco Moretti]

CheezWiz wrote:
>
> I think you are still trying to mix RECEPTION with PERCEPTION.
>
> There is no biological mechanism to receive "Orange" wavelengths.
> If a fish even detects that a 632 nm laser is there, then it must have red
> cones in its eye.
> Unless its green cones can see all the way up to the red spectrum of the
> chart.
>
> Orange would be a mix of Red and Green wavelengths, but a laser is
> MONOCHROMATIC.
> A fish without a cone that can detect that frequency will see no light and
> no shadow from a red laser pointer.

It took me the longest time to integrate the information I learned in
art, (The three primary colors are Red, Blue and Yellow)
computer/biology classes (The three primary colors are Red, Green and
Blue) and Physics. (There is a spectrum of light, a rainbow of Red,
Orange, Yellow, Green, Blue and Violet, each present and distinct).

Here's my current understanding:

Visible light ranges from about 400 nm to 700 nm.
(http://en.wikipedia.org/wiki/Visible_light)
If you look at monochromatic light at particular wavelengths, you see a
particular color
(http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html):

420 nm - Violet
475 nm - Blue
510 nm - Green
570 nm - Yellow
590 nm - Orange
650 nm - Red

This is monochromatic light, so it only has one identity. It is in no
way accurate to say that 420 nm light is a "mix" of Red and Blue light.
It isn't. So how do we reconcile this with our common perception that
Violet/Purple is a mix of Red and Blue, and with the observation that we
can make something look purple by mixing Red and Blue light, say on a
computer monitor?

Our (most people's) eyes have three sets of color sensitive cells
(cones) on our retina. These are normally refered to by the color we
percieve when they are excited: Red, Green, and Blue. But the cells
don't absorb monochromatic light - they absorb over a range of lights.
(http://en.wikipedia.org/wiki/Cone_cell) So monochromatic 450 nm light
excites the "Blue" cone most, but also exictes the "Red" and "Green"
cones to some degree (see chart on link). Since "Blue" is excited most,
we see 450 nm light as Blue. At 400 nm, the "Blue" cone is excited, but
the Red and Green cones also get significant excitation. Our brain
then combines the signals from all three cone cells, and comes up with
the perception of "Purple"

Now here's the key part - when the brain is combining the signals from
all of the cones, it has no idea which wavelenghts of light the eye
received - it only sees the strength of the excitation from each of the
cones. If you matched the level of excitation seen in each of the three
cones produced by a given intensity of 420 nm monochromatic light with a
mix of wavelenghts (say 450 nm for the "Blue" cone, 540 nm for the green
and 600 nm for the red) the brain can't tell the difference, so would
see the same color in both cases. So "Purple" isn't 420 nm, the exact
same color effect can also be made by mixing other wavelenghts. (The
trick is to match the levels of excitation seen by each cone)

So even if the laser pointer is monochromatic at 632 nm, and is "Red" to
us, it also excites the "Green" cone as well - if a fish doesn't have
the "Red" cone, a "Green" or "Yellow" or even a "Cyan" cone could pick
up the light signal, if it's absorption envelope was spread out enough.
Granted, it wouldn't likely seem as bright as for a creature with a
dedicated "Red" cone, but it still would be perceptable.

Also note that the diagrams on the link are also averages for normal
humans. It happens quite frequently that the absorption spectra of the
cone cells varies, depending on what genes you get. This is especially
true of the Red and Green cones, which are so similar. Often you can get
red and green cones which don't differ all that much in absorption
spectra - this leads to Red-Green color blindness. And how different the
spectra are determines how severe the color blindness is.

Now the genes for the Red and Green cones are on the X-chromosome in
humans. Males are stuck with one of each, but Females have two of each.
And since they can vary so much, sometimes you get a female who has
cones with three distinct spectra, versus the normal Red/Green pair.
This gives them an extra dimention to color perception. They're called
tetrachromats (http://en.wikipedia.org/wiki/Tetrachromat).

The key point for this post is that color itself is all in your mind.
There isn't a "Green" in nature, only varying intensities of different
wavelenghts of light. "Green" is something your brain makes up to help
you understand the world. Trying to apply it to someone with a different
color sensing cells, or especially a different species is likely to lead
to confusion.

P.S. Here's something that royally confused my elementary school class
when I was about 10 years old - Is the green that I see the same as the
green you see? How could you tell?

[CheezWiz]

Well that is exactly the information I have been unable to find.
What exactly are the wavelength ranges over which a particular R-G-B cone
can detect.
Then you have to take it one step farther and ask what luminosity it
perceives over that wavelength envelope.

To simply say that a fish or a human cannot "see" red is really too broad of
a statement to make since as you have stated, the other cones may detect
that wavelength of light, just at a lower luminosity than a cone dedicated
to the red spectrum.

If the green, blue, and possibly even rods can detect a 640 nm "red" laser
pointer, then it does in fact see "red" as far as the wavelength is
concerned..
However, it may perceive it as something totally different from what we or
possibly one of its own kind perceive...

I should have said that "orange would be a mix of reception of the red and
green cones" to get closer to what I was trying to say. I work an IT job
with a guy who just graduated with a degree in Elementary Education with a
focus on natural science. That sounds just like something he would have
said..

Very good post Rocco.

ps, do identical twins see the same green?

CW

"Rocco Moretti" > wrote in message
...
> CheezWiz wrote:
>>
>> I think you are still trying to mix RECEPTION with PERCEPTION.
>>
>> There is no biological mechanism to receive "Orange" wavelengths.
>> If a fish even detects that a 632 nm laser is there, then it must have
>> red cones in its eye.
>> Unless its green cones can see all the way up to the red spectrum of the
>> chart.
>>
>> Orange would be a mix of Red and Green wavelengths, but a laser is
>> MONOCHROMATIC.
>> A fish without a cone that can detect that frequency will see no light
>> and no shadow from a red laser pointer.
>
> It took me the longest time to integrate the information I learned in art,
> (The three primary colors are Red, Blue and Yellow) computer/biology
> classes (The three primary colors are Red, Green and Blue) and Physics.
> (There is a spectrum of light, a rainbow of Red, Orange, Yellow, Green,
> Blue and Violet, each present and distinct).
>
> Here's my current understanding:
>
> Visible light ranges from about 400 nm to 700 nm.
> (http://en.wikipedia.org/wiki/Visible_light)
> If you look at monochromatic light at particular wavelengths, you see a
> particular color
> (http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html):
>
> 420 nm - Violet
> 475 nm - Blue
> 510 nm - Green
> 570 nm - Yellow
> 590 nm - Orange
> 650 nm - Red
>
> This is monochromatic light, so it only has one identity. It is in no way
> accurate to say that 420 nm light is a "mix" of Red and Blue light. It
> isn't. So how do we reconcile this with our common perception that
> Violet/Purple is a mix of Red and Blue, and with the observation that we
> can make something look purple by mixing Red and Blue light, say on a
> computer monitor?
>
> Our (most people's) eyes have three sets of color sensitive cells (cones)
> on our retina. These are normally refered to by the color we percieve when
> they are excited: Red, Green, and Blue. But the cells don't absorb
> monochromatic light - they absorb over a range of lights.
> (http://en.wikipedia.org/wiki/Cone_cell) So monochromatic 450 nm light
> excites the "Blue" cone most, but also exictes the "Red" and "Green" cones
> to some degree (see chart on link). Since "Blue" is excited most, we see
> 450 nm light as Blue. At 400 nm, the "Blue" cone is excited, but the Red
> and Green cones also get significant excitation. Our brain then combines
> the signals from all three cone cells, and comes up with the perception of
> "Purple"
>
> Now here's the key part - when the brain is combining the signals from all
> of the cones, it has no idea which wavelenghts of light the eye received -
> it only sees the strength of the excitation from each of the cones. If you
> matched the level of excitation seen in each of the three cones produced
> by a given intensity of 420 nm monochromatic light with a mix of
> wavelenghts (say 450 nm for the "Blue" cone, 540 nm for the green and 600
> nm for the red) the brain can't tell the difference, so would see the same
> color in both cases. So "Purple" isn't 420 nm, the exact same color effect
> can also be made by mixing other wavelenghts. (The trick is to match the
> levels of excitation seen by each cone)
>
> So even if the laser pointer is monochromatic at 632 nm, and is "Red" to
> us, it also excites the "Green" cone as well - if a fish doesn't have the
> "Red" cone, a "Green" or "Yellow" or even a "Cyan" cone could pick up the
> light signal, if it's absorption envelope was spread out enough. Granted,
> it wouldn't likely seem as bright as for a creature with a dedicated "Red"
> cone, but it still would be perceptable.
>
> Also note that the diagrams on the link are also averages for normal
> humans. It happens quite frequently that the absorption spectra of the
> cone cells varies, depending on what genes you get. This is especially
> true of the Red and Green cones, which are so similar. Often you can get
> red and green cones which don't differ all that much in absorption
> spectra - this leads to Red-Green color blindness. And how different the
> spectra are determines how severe the color blindness is.
>
> Now the genes for the Red and Green cones are on the X-chromosome in
> humans. Males are stuck with one of each, but Females have two of each.
> And since they can vary so much, sometimes you get a female who has cones
> with three distinct spectra, versus the normal Red/Green pair. This gives
> them an extra dimention to color perception. They're called tetrachromats
> (http://en.wikipedia.org/wiki/Tetrachromat).
>
> The key point for this post is that color itself is all in your mind.
> There isn't a "Green" in nature, only varying intensities of different
> wavelenghts of light. "Green" is something your brain makes up to help you
> understand the world. Trying to apply it to someone with a different color
> sensing cells, or especially a different species is likely to lead to
> confusion.
>
> P.S. Here's something that royally confused my elementary school class
> when I was about 10 years old - Is the green that I see the same as the
> green you see? How could you tell?

[George]

"CheezWiz" > wrote in message
...
> Well that is exactly the information I have been unable to find.
> What exactly are the wavelength ranges over which a particular R-G-B cone can
> detect.
> Then you have to take it one step farther and ask what luminosity it perceives
> over that wavelength envelope.
>
> To simply say that a fish or a human cannot "see" red is really too broad of a
> statement to make since as you have stated, the other cones may detect that
> wavelength of light, just at a lower luminosity than a cone dedicated to the
> red spectrum.
>
> If the green, blue, and possibly even rods can detect a 640 nm "red" laser
> pointer, then it does in fact see "red" as far as the wavelength is
> concerned..
> However, it may perceive it as something totally different from what we or
> possibly one of its own kind perceive...
>
> I should have said that "orange would be a mix of reception of the red and
> green cones" to get closer to what I was trying to say. I work an IT job with
> a guy who just graduated with a degree in Elementary Education with a focus on
> natural science. That sounds just like something he would have said..
>
> Very good post Rocco.
>
> ps, do identical twins see the same green?
>
> CW

I happen to be an identical twin. Not only do we both have similarly bad
eyesight, each of us somehow managed to find the same optometrist without the
other knowing about it.

[CheezWiz]

In numerous tests, twins are able to communicate flashcards "psychically"
with greater than 60% accuracy..
Not all, but some.

Have you two ever participated in one of those tests?

"George" > wrote in message
news:IBPee.52427$r53.32134@attbi_s21...
>
> "CheezWiz" > wrote in message
> ...
>> Well that is exactly the information I have been unable to find.
>> What exactly are the wavelength ranges over which a particular R-G-B cone
>> can detect.
>> Then you have to take it one step farther and ask what luminosity it
>> perceives over that wavelength envelope.
>>
>> To simply say that a fish or a human cannot "see" red is really too broad
>> of a statement to make since as you have stated, the other cones may
>> detect that wavelength of light, just at a lower luminosity than a cone
>> dedicated to the red spectrum.
>>
>> If the green, blue, and possibly even rods can detect a 640 nm "red"
>> laser pointer, then it does in fact see "red" as far as the wavelength is
>> concerned..
>> However, it may perceive it as something totally different from what we
>> or possibly one of its own kind perceive...
>>
>> I should have said that "orange would be a mix of reception of the red
>> and green cones" to get closer to what I was trying to say. I work an IT
>> job with a guy who just graduated with a degree in Elementary Education
>> with a focus on natural science. That sounds just like something he would
>> have said..
>>
>> Very good post Rocco.
>>
>> ps, do identical twins see the same green?
>>
>> CW
>
> I happen to be an identical twin. Not only do we both have similarly bad
> eyesight, each of us somehow managed to find the same optometrist without
> the other knowing about it.
>

[George]

"CheezWiz" > wrote in message
...
> In numerous tests, twins are able to communicate flashcards "psychically" with
> greater than 60% accuracy..
> Not all, but some.
>
> Have you two ever participated in one of those tests?

No, but then, when I took psychology and anthropolgy in college, I read papers
that showed that a 50% success rate can be duplicated randomly, so I don't
really have any faith in anyone having "psychic" abilities. I've probably now
opened a can of worms, and expect to see a lot of argument over the issue.
Sorry about that.

[CheezWiz]

"George" > wrote in message
news:CJSee.61128$WI3.12917@attbi_s71...
>
> "CheezWiz" > wrote in message
> ...
>> In numerous tests, twins are able to communicate flashcards "psychically"
>> with greater than 60% accuracy..
>> Not all, but some.
>>
>> Have you two ever participated in one of those tests?
>
> No, but then, when I took psychology and anthropolgy in college, I read
> papers that showed that a 50% success rate can be duplicated randomly, so
> I don't really have any faith in anyone having "psychic" abilities. I've
> probably now opened a can of worms, and expect to see a lot of argument
> over the issue. Sorry about that.
>

Naah, wrong group, we would have to move the thread to another group... 8)

[George]

"CheezWiz" > wrote in message
...
>
> "George" > wrote in message
> news:CJSee.61128$WI3.12917@attbi_s71...
>>
>> "CheezWiz" > wrote in message
>> ...
>>> In numerous tests, twins are able to communicate flashcards "psychically"
>>> with greater than 60% accuracy..
>>> Not all, but some.
>>>
>>> Have you two ever participated in one of those tests?
>>
>> No, but then, when I took psychology and anthropolgy in college, I read
>> papers that showed that a 50% success rate can be duplicated randomly, so I
>> don't really have any faith in anyone having "psychic" abilities. I've
>> probably now opened a can of worms, and expect to see a lot of argument over
>> the issue. Sorry about that.
>>
>
> Naah, wrong group, we would have to move the thread to another group... 8)

That's good. I don't want to be responsible for starting a flame war. This
newsgroup is too useful to see it trashed.