Changing the color of a LED is it possiable?

grasshopper

I was thinking that the propeller could change the color of a white led by modulating it at the desired color. Do you think it is possible? For example the wavelength of blue is 450–495 nm and this can be calculated as a frequency of 2.2 - 2.02 Mhz. So the idea is to run a PWM or a type of freqout on a white led making it changes its color.

Comments please...

Bruce Bates

grasshopper -

It's the composition of the strata on which the LED is manufactured which gives it the specific color that it emits, not the frequency of the current passing through it.

In other words (say) red and green LED's are made of different base materials. Additionally, they operate at different voltages.

Regards,

Bruce Bates

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When all else fails, try inserting a new battery.

Beau Schwabe

grasshopper,

Your off by a couple of units.

2.2mHz has a wavelength of 447.08 feet ... you need it to be in meters...

For 450nm you would need a frequency of 6.6621e+8 mHz or 666,210 gigaHz or 666.21 teraHz

likewise for 495 nm, you would need a frequency of 6.0564e+8 mHz .... ... or 605.64 teraHz

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Lab Rat

i wish it was possible that would be cool

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Parallax posesses power beyond belief.

Believe in it.

Bruce Bates

Folks -

It can certainly be done with a multi-color LED such as this one:
http://www.sunledusa.com/SearchResult.asp?Series=XSxxxxxx99W&SubCategoryDescription=Multi-Color LED Lamps

It's essentially 3 LED's in one package. You drive each of them differently, to achieve the color mix you want. I don't have a link for it handy, but someone makes a driver chip for these multi-color LED's so that you don't need to worry about the single threaded nature of the PBASIC Stamp. A seach of this forum should reveal it however.

Regards,

Bruce Bates

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When all else fails, try inserting a new battery.

Bruce Bates

Folks -

Here is a DUAL tri-color LED driver which does everything but make soup, from National Semiconductor:
http://www.national.com/pf/LP/LP3931.html

Regards,

Bruce Bates

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When all else fails, try inserting a new battery.

grasshopper

Yea I miss calculated forgot the formula f * λ = c instead i just used the inverse of the F. I still think it can be done but some real high speeds are needed.

Beau Schwabe

Bruce,

True, a tri-color led is the way to go ... however the original question was asking about modulating a white led to produce various colors.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

GICU812

Here is a DUAL tri-color LED driver which does everything but make soup, from National Semiconductor:
http://www.national.com/pf/LP/LP3931.html

If you want soup, you have to get the LP3931-S
·

heater

On the other hand many years ago, in the time when colour TV was only just spreading in the UK, the BBC science program "Tomorrows World" demonstrated a technique of produce the perception of colours on black and white TVs. Apparently this involved rapidly flashing and moving monochrome images.

I did not see that show but some of my friends who did said they had indeed seen colours. Trouble is everyone saw different colours.

Since then I have noticed colours for fleeting moments during rapidly moving scenes on a monochrome TV which led me to spend some minutes staring at the "snow" of a black and white TV that is not tuned to any channel. Sure enough from those bright random flashing white speckles colours emerged eventually.

It's best not to do these kinds of experiment to often else your friends start to thing you've lost your mind !

Check this story www.writer2001.com/captkang.htm

and this en.wikipedia.org/wiki/Benham_disk

So now let's see what we can do with a bunch of flashing white LEDs

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For me, the past is not over yet.

hippy

Interesting. Following a Wikipedia link and I got to this -

www.michaelbach.de/ot/col_benham/index.html

I can definitely see a dark grass green / dark blue there and clicking 'reverse' does swap the colours.

grasshopper

Well seriously thinking could one use the propeller - connecting it to a frequency multiplier then into the LED. It would work right? I figure that a frequency of 660Ghz would be needed. Wow the clock multiple would have to be in the range of impossible.

Lab Rat

grasshopper said...
·Wow the clock multiple would have to be in the range of impossible.

i like that what have you got to loose having fun i am sure if you screw things up it will be amusing. maybe the led will explode or maybe it will just die.
i have seen what happens to neon lamps when you put too high a voltage in them (my friends said to stop shooting shrapnal at them

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Parallax posesses power beyond belief.

Believe in it.

heater

Hippy: I've tried a couple of those Benhams Top demos on the net this evening, none of them worked for me. Could be me, could be the LCD on my laptop. Either way I would not trust it as a demo because, well if you're watching it on a colour screen how do you know that the effect isn't due to some moire fringe effect with different colour pixels? Like the crazy patterns we get on news readers ties from time to time. I have to try this for real. But my question is can we get the same effect with a handful of stobing white LEDs?

Grasshopper: Think about it. If you could multiply the Prop output frequency up to optical levels you would not need the LED, just look at the output of your multiplier !

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For me, the past is not over yet.

Post Edited (heater) : 10/16/2008 9:09:42 PM GMT

Timothy D. Swieter

Another point about modifying a white LED to produce other colors is that the white LED doesn't always contian all the other colors. What I mean is the physics of the semiconductor material in there. White LED can often be blue LEDs with another material that phosprizes (spelling?) to generate a white LED. If you look at the spectrum data of a white LED it doesn't contain healthy amounts of other wavelengths to try and seperate them out.

On the idea of tri-colored LED controll, I use RGB LEDs and have a product called the LED Painter that uses the Texas Instrument TLC5940 IC. The LED Painter has 16 channels of RGB LED control. I am working on a new product too for all the RGB LED tinkers, but that might be a few weeks away.

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Timothy D. Swieter, E.I.

www.brilldea.com·- Prop Blade, LED Painter, RGB LEDs, uOLED-IOC, eProto fo SunSPOT, BitScope
www.sxmicro.com - a blog·exploring the SX micro
www.tdswieter.com

Beau Schwabe

grasshopper,

"connecting it to a frequency multiplier then into the LED. It would work right?" - No, the propagation delay of the LED for it to turn OFF and ON would not be able to keep up... typical propagation delay of an LED is about 5ns. (100MHz)

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

LilDi

Good luck finding an LED with 666.21 teraHz bandwidth

pharseid

If you could actually produce an oscillator of that frequency, would you need an LED? Would an antenna directly produce light (or maybe an array of antennas since a full-wave antenna at those frequencies would be pretty small).

-phar

heater

Often antenna for optical frequencies are atom sized, think sodium vapour lamps en.wikipedia.org/wiki/Sodium_vapor_lamp
Certainly I would regard a solid state laser diode (basically LED technology) as an oscillator.
Perhaps a normal LED is not an oscillator as such as it's output is incoherent.

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For me, the past is not over yet.

grasshopper

Perhaps a type of biological or chemical or a protein antenna would work [noparse]:)[/noparse]
an Led would defiantly not work

Dam this was posted in a strange way. Oh well Its in the correct place now.

Tracy Allen

It's appropriate to bring up laser diodes. The output of some diodes is a very narrow peak at one frequency ("single mode") and often the frequency of that peak can be tuned by varying the current through the diode or some other parameter. The practical application of this is the detection of gasses like CO2 or NH3 at very sensitive levels without interference. Gasses absorb light at very specific frequencies. A laser single mode output frequency is chosen that sits right on top of one of those frequencies for the gas of interest and is swept up and down. Google, "Tuneable Diode Laser Spectrometry (TDLS)". This is much more sensitve than NDIR, which is based on fixed frequencies and interference filters. The tuning range of the lasers is not much, so an instrument that has to detect several gases will have to have several lasers. The frequency of the laser is based on the semiconductor and on the mirrors. The diagram shows the output of a particular single mode VCSEL (vertical cavity surface emitting laser) as current is varied. The tuning range (color variation) in only a few nm.



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Tracy Allen
www.emesystems.com