How to get Yellow?

I found the frequencies for both visible red light and visible green 
light, but when I added the phasors of each together I didn't get the 
phasor for the frequency of yellow light or anything even close.

I am wondering how red and green light combine to make yellow if their 
phasors don't add up.

Here were my phasors:


# red at ~ 483 THz
red = e^(j*483870967741935*t)

# green at ~606 THz
green = e^(j*606060606060606.0*t)

# How come yellow at ~526 THz is not even close?
red + green

On Wed, 17 Aug 2011 14:40:18 -0400, Billy Mays <noway@nohow.com> wrote:

>I found the frequencies for both visible red light and visible green 
>light, but when I added the phasors of each together I didn't get the 
>phasor for the frequency of yellow light or anything even close.
>
>I am wondering how red and green light combine to make yellow if their 
>phasors don't add up.
>
>Here were my phasors:
>
>
># red at ~ 483 THz
>red = e^(j*483870967741935*t)
>
># green at ~606 THz
>green = e^(j*606060606060606.0*t)
>
># How come yellow at ~526 THz is not even close?
>red + green

Because red light plus green light becomes yellow light is largely a
result of how that information gets processed in the visual cortex, not
simply the physics of the result. It's also variable by the individual;
some tend to see a "reddish-green" or "greenish-red" more than simply a
yellow hue. See
<http://www.sciencemag.org/content/221/4615/1078.abstract?sid=851edf3f-13ef-4d88-9b1f-3ea38fa02aec>

-- 
Rich Webb     Norfolk, VA

Billy Mays <noway@nohow.com> wrote:
> I found the frequencies for both visible red light and visible green 
> light, but when I added the phasors of each together I didn't get the 
> phasor for the frequency of yellow light or anything even close.

> I am wondering how red and green light combine to make yellow if their 
> phasors don't add up.

They don't, as those who park cars in parking lots lit with
sodium vapor lamps know.

They don't make yellow until they hit the receptors in your eye
that process them as yellow.

Sodium vapor lamps make yellow light, but not red or green.
You can't tell a red car from a green car, thought you would
for an incandescent lamp with a yellow filter.

-- glen

On Aug 17, 2:40&#4294967295;pm, Billy Mays <no...@nohow.com> wrote:
> I found the frequencies for both visible red light and visible green
> light, but when I added the phasors of each together I didn't get the
> phasor for the frequency of yellow light or anything even close.
>
> I am wondering how red and green light combine to make yellow if their
> phasors don't add up.
>
> Here were my phasors:
>
> # red at ~ 483 THz
> red = e^(j*483870967741935*t)
>
> # green at ~606 THz
> green = e^(j*606060606060606.0*t)
>
> # How come yellow at ~526 THz is not even close?
> red + green

You didn't give this much thought beforehand. I'm sure you know that
adding two signals of different frequencies gives you a signal with
two frequencies, not one with their average frequency. Think of a
chord (or two tones) on a piano.

A normal human eye has three color receptors. Each is more or less
sensitive to light across the visible spectrum, but their response
curves are different; each peaks at a different frequency. What we
perceive as color is determined by the relative excitations of the
three sensors.

Color photography, film or digital, uses three color receptors. Now
you know why.

Jerry
--
Engineering is the art of making what you want from things you can get.

On Wed, 17 Aug 2011 19:15:08 +0000, glen herrmannsfeldt wrote:

> Billy Mays <noway@nohow.com> wrote:
>> I found the frequencies for both visible red light and visible green
>> light, but when I added the phasors of each together I didn't get the
>> phasor for the frequency of yellow light or anything even close.
> 
>> I am wondering how red and green light combine to make yellow if their
>> phasors don't add up.
> 
> They don't, as those who park cars in parking lots lit with sodium vapor
> lamps know.
> 
> They don't make yellow until they hit the receptors in your eye that
> process them as yellow.
> 
> Sodium vapor lamps make yellow light, but not red or green. You can't
> tell a red car from a green car, thought you would for an incandescent
> lamp with a yellow filter.
> 
> -- glen

Hey!  I've been trying for years to think of a way to get non color-blind 
people to experience what it's like to be red-green colorblind -- maybe 
this is it!

-- 
www.wescottdesign.com

On Wed, 17 Aug 2011 14:40:18 -0400, Billy Mays wrote:

> I found the frequencies for both visible red light and visible green
> light, but when I added the phasors of each together I didn't get the
> phasor for the frequency of yellow light or anything even close.
> 
> I am wondering how red and green light combine to make yellow if their
> phasors don't add up.
> 
> Here were my phasors:
> 
> 
> # red at ~ 483 THz
> red = e^(j*483870967741935*t)
> 
> # green at ~606 THz
> green = e^(j*606060606060606.0*t)
> 
> # How come yellow at ~526 THz is not even close? red + green

Understand this:
http://en.wikipedia.org/wiki/Color_perception

Much will become clear.

-- 
www.wescottdesign.com

On Wed, 17 Aug 2011 15:57:03 -0500, Tim Wescott <tim@seemywebsite.com>
wrote:

>On Wed, 17 Aug 2011 19:15:08 +0000, glen herrmannsfeldt wrote:
>
>> Billy Mays <noway@nohow.com> wrote:
>>> I found the frequencies for both visible red light and visible green
>>> light, but when I added the phasors of each together I didn't get the
>>> phasor for the frequency of yellow light or anything even close.
>> 
>>> I am wondering how red and green light combine to make yellow if their
>>> phasors don't add up.
>> 
>> They don't, as those who park cars in parking lots lit with sodium vapor
>> lamps know.
>> 
>> They don't make yellow until they hit the receptors in your eye that
>> process them as yellow.
>> 
>> Sodium vapor lamps make yellow light, but not red or green. You can't
>> tell a red car from a green car, thought you would for an incandescent
>> lamp with a yellow filter.
>> 
>> -- glen
>
>Hey!  I've been trying for years to think of a way to get non color-blind 
>people to experience what it's like to be red-green colorblind -- maybe 
>this is it!
>
>-- 
>www.wescottdesign.com

Well, bummer.   So this show would be totally lost on you:

http://redgreen.com/

Despite being Canadian, it's pretty funny stuff.     ;)


Eric Jacobsen
http://www.ericjacobsen.org
http://www.dsprelated.com/blogs-1//Eric_Jacobsen.php

On 8/17/2011 3:15 PM, glen herrmannsfeldt wrote:
> Billy Mays<noway@nohow.com>  wrote:
>> I found the frequencies for both visible red light and visible green
>> light, but when I added the phasors of each together I didn't get the
>> phasor for the frequency of yellow light or anything even close.
>
>> I am wondering how red and green light combine to make yellow if their
>> phasors don't add up.
>
> They don't, as those who park cars in parking lots lit with
> sodium vapor lamps know.
>
> They don't make yellow until they hit the receptors in your eye
> that process them as yellow.
>
> Sodium vapor lamps make yellow light, but not red or green.
> You can't tell a red car from a green car, thought you would
> for an incandescent lamp with a yellow filter.
>
> -- glen


Would it then be possible to make a car from a combination of yellow and 
blue paint to make it cyan colored?  Then, make a lamp that emits cyan 
light (somewhere around ~610 Thz).  Since neither of the two paints are 
exactly cyan, no light should reflect off the car, even though the car 
paint and the light would appear to be the same color?

On Aug 17, 6:05&#4294967295;pm, Billy Mays <no...@nohow.com> wrote:
> On 8/17/2011 3:15 PM, glen herrmannsfeldt wrote:
>
>
>
>
>
>
>
>
>
> > Billy Mays<no...@nohow.com> &#4294967295;wrote:
> >> I found the frequencies for both visible red light and visible green
> >> light, but when I added the phasors of each together I didn't get the
> >> phasor for the frequency of yellow light or anything even close.
>
> >> I am wondering how red and green light combine to make yellow if their
> >> phasors don't add up.
>
> > They don't, as those who park cars in parking lots lit with
> > sodium vapor lamps know.
>
> > They don't make yellow until they hit the receptors in your eye
> > that process them as yellow.
>
> > Sodium vapor lamps make yellow light, but not red or green.
> > You can't tell a red car from a green car, thought you would
> > for an incandescent lamp with a yellow filter.
>
> > -- glen
>
> Would it then be possible to make a car from a combination of yellow and
> blue paint to make it cyan colored? &#4294967295;Then, make a lamp that emits cyan
> light (somewhere around ~610 Thz). &#4294967295;Since neither of the two paints are
> exactly cyan, no light should reflect off the car, even though the car
> paint and the light would appear to be the same color?

There's still a lot of misconception in your question. Mix yellow and
blue paint and you get green. Why? because the yellow paint absorbs
the blue end of the spectrum, and the blue paint absorbs the red end,
leaving a band in the middle that we see as green. The result of
adding bands of light, as a color monitor does, are entirely
different. Your color monitor has three phosphors, red, green, and
blue. (The long end, the middle, and the short end of the visible
spectrum.) They are mixed in different proportions to create the color
palette that is displayed. Although every color that can be displayed
can be matched by light of a single frequency, only those (relatively
narrow) bands are generated by a color screen.

Tim and Rich gave you links to read. Read then. It will probably save
me some typing.

Jerry
--
Engineering is the art of making what you want from things you can get.

Tim Wescott <tim@seemywebsite.com> wrote:

(snip, I wrote)
>> Sodium vapor lamps make yellow light, but not red or green. You can't
>> tell a red car from a green car, thought you would for an incandescent
>> lamp with a yellow filter.

> Hey!  I've been trying for years to think of a way to get non color-blind 
> people to experience what it's like to be red-green colorblind -- maybe 
> this is it!

Just to be sure, that is low pressure sodium lamps.

Some years ago the place my father worked one day replaced all the
lights in the parking lot with low pressure sodium lamps.  People
had a very hard time finding their cars.

Also, the city of San Jose CA uses them for street lights.
There is an nearby observatory that was worried when the city was
planning a change to high pressure sodium.  As a test, the city
put in low pressure lamps on one street.  After no complaints, they
switched all the lamps over.

Mercury and LPS are easy for astronomers to filter, but HPS has
a broad spectrum and can't be filtered out.

-- glen