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Christmas Tree Lights

Mojo

Mostly harmless
Mojo
Joined
Jul 22, 2004
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A couple of weeks ago I was in a pub where they had some purple christmas tree lights. When looked at through the edges of my spectacles, where chromatic aberration comes into play a little, the purple colour of the bulbs was split into red and blue components.

For some reason, rapid eye movements, in conjunction with the flickering of the lights, also split the purple into red and blue components.

How does this happen? Are the two colours from a single bulb somehow being produced at different points on the AC cycle, perhaps?
 
Bikewer said:
More likely the prismatic effect caused by both the narrow bulb's glass and your specs, I'd think.
Click to expand...
This explains the colours being separated when looked at through the edges of my specs, but not the separation when the eyes were moving. I'll elaborate:

Because the lights flicker, if you move your eyes rapidly, the individual bulbs appear as a series of individual flashes, rather than as a continuous line. They also appeared as an alternating series of red and blue flashes, rather than (as I would have expected) a series of purple flashes. This suggests that the red and blue lights, which were being produced by a single bulb, were not occuring together, but (perhaps) at different parts of the AC cycle, although I don't see how this could happen.

This happened whether I was wearing my specs or not, and the phenomenon was also observed by everyone else in the room, whether or not they wore glasses.
 
My guess is that they are bicolor blue/red LEDs that have a common cathode and a red and a blue anode. Rapidly switching the power back and forth between the anodes fuses the red and blue to additively produce purple. If the switching rate is near the critical fusion frequency, under certain viewing conditions you'll see the two different colors.
The same thing is done with bicolor red/green LEDs. They can produce red, green, or a orange-yellow fusion of the two.
 
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I've seen light strips where they have blue, red, and green lights... the strip had sequences where it would create patterns of various lights... the effect was kinda neat, where you had an image of purple, but you could still distinguish the blue and red individually if you looked at the individual lights.
 
I have a juggling ball that has LED lights in it. When you turn it on, it cycles through like 7 diffferent colors, including white. I was very excited to discover, when I opened it up that there were only 3 LEDs making those 7 colors.

Can you guess the colors?


Edited to add: When I worked for Mad Science, teaching kids about science, I would use my juggling ball to teach about light.
 
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Magent, cyan, and yellow. Same as the colors of ink in your ink jet printer, and ther pixels on your monitor. Millions of color possible, but 7 was the limit of the chip inside of your ball.
 
Magenta, cyan and yellow are used in subtractive color mixing, as in printing.
We are talking about additive color mixing in this case.
 
And when you're printing, you also need a separate black cartridge. With a monitor, the pixels are red, green, and blue.
 
Jeff Corey said:
My guess is that they are bicolor blue/red LEDs that have a common cathode and a red and a blue anode. Rapidly switching the power back and forth between the anodes fuses the red and blue to additively produce purple. If the switching rate is near the critical fusion frequency, under certain viewing conditions you'll see the two different colors.
The same thing is done with bicolor red/green LEDs. They can produce red, green, or a orange-yellow fusion of the two.
Click to expand...

Wouldn't that be kind of pricey for a string of Christmas lights?
 
Not sure, but I don't think so. When I was playing around with the bicolor r/g ones a few years ago, they were about $1.29 at Radio shack.
 
Jeff Corey said:
Not sure, but I don't think so. When I was playing around with the bicolor r/g ones a few years ago, they were about $1.29 at Radio shack.
Click to expand...


And replacement bulbs for plain Italian lights are 6 for a quarter. I don't think people will pay premium prices for lights they will use for three weeks a year.
 
Jeff Corey said:
Magenta, cyan and yellow are used in subtractive color mixing, as in printing.
We are talking about additive color mixing in this case.
Click to expand...

Printing and monitors are both examples of additive, filters on cameras are subtractive. The magenta and cyan are simply more technical names for redish and blueish. Using green instead of yellow is more a matter of choice of pallate.
 
No. The primary colors are red, green and blue. There is no yellow on a TV set or monitor. The perception of yellow is produced by the pointillistic additive combination of red and green.
 
Jeff Corey said:
No. The primary colors are red, green and blue. There is no yellow on a TV set or monitor. The perception of yellow is produced by the pointillistic additive combination of red and green.
Click to expand...

OK, but...

Classical subtractive colors are red, blue, and yellow.

So it follows that one could make an additive set from magenta, cyan, and orange.

When I was a kid, I tried it, and it worked.
 
My juggling ball had a red, blue, and green light in it.

These were the combinations it lit up:

r made red
b made blue
g made green
rb made purple
rg made yellow
bg made cyan
rbg made white
 
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