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'[EE] LED color mixing: RGB...O?'
2006\11\27@120338 by Mike Hord

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I just bought some LEDs from Digikey/Mouser for a color mixing
project I'm thinking of playing around with (why paint when you
can light?), but I'm a little confused by the fact that the "matched"
LEDs I bought come in FOUR colors: RGB and orange.

This is new to me, and you-know-whoogle doesn't have anything
to offer.

I accidentally bought GBO in my first order, so I picked up some
red ones from Mouser (same manufacturer part number, but
Mouser doesn't have a minimum order)(I prefer Digikey due to
proximity).  I have all four- am I "supposed" to use them all?

Mike H.

2006\11\27@122541 by William Chops Westfield

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On Nov 27, 2006, at 9:03 AM, Mike Hord wrote:

> I'm a little confused by the fact that the "matched"
> LEDs I bought come in FOUR colors: RGB and orange.

Apparently RED leds are a big no-no on commercial equipment;
perhaps the OGB selection is for that sort of application?

BillW

2006\11\27@125232 by Marcel duchamp

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William Chops Westfield wrote:
> On Nov 27, 2006, at 9:03 AM, Mike Hord wrote:
>
> Apparently RED leds are a big no-no on commercial equipment;
>
> BillW

Bill, could you elaborate on that one?  Was that tongue-in-cheek or serious?

2006\11\27@131642 by William Chops Westfield

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On Nov 27, 2006, at 9:52 AM, Marcel duchamp wrote:

>> Apparently RED leds are a big no-no on commercial equipment;
>
> Bill, could you elaborate on that one?
>   Was that tongue-in-cheek or serious?
>
Serious, although I don't know the details.  At some point there
was a real fire-drill here to eliminate the use of red LEDs; I suspect
some telco or european standard that reserves red for truly "critical"
notifications.  I'll see if I can find out...

BillW

2006\11\27@134422 by Steve Baldwin
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That will probably be so that they can be used in a traffic or automotive
application. You can make orange from green and red, but a failure results
in a red or a green where an orange should be. ie. It doesn't fail safe (see
earlier thread).  Traffic lights are the obvious one. It's pretty tightly regulated
for roadage signs as well as the colour infers the importance.

Steve.


On 27 Nov 2006 at 11:03, Mike Hord wrote:

{Quote hidden}

> --

2006\11\27@135954 by Alden Hart

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Many of the higher-end LED assemblies used for stage and architectural
lighting use this mix - they call it RBGA (amber). Some even use white,
as well. I guess you get a better mix gamut that way and have more
control over the color and how natural you can make the white balance.
It's also worth noting that they tend to use 16 bit controls on the PWM
for dimming. It seems that fewer bits than this (i.e. less temporal
resolution in the pulses) gives you visible steps (quantization errors)
at low light levels.

Alden

Steve Baldwin wrote:
{Quote hidden}

>> --

2006\11\27@142157 by Andre Abelian

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Bill,

Combination of Red and Green gives Orange
what's wrong with red?

Andre



-----Original Message-----
From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]On Behalf
Of William "Chops" Westfield
Sent: Monday, November 27, 2006 9:26 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] LED color mixing: RGB...O?


On Nov 27, 2006, at 9:03 AM, Mike Hord wrote:

> I'm a little confused by the fact that the "matched"
> LEDs I bought come in FOUR colors: RGB and orange.

Apparently RED leds are a big no-no on commercial equipment;
perhaps the OGB selection is for that sort of application?

BillW

2006\11\27@180909 by alan smith

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be interested as well....since I'm using a blue/red LED combo

William Chops Westfield <westfwspamKILLspammac.com> wrote:  
On Nov 27, 2006, at 9:52 AM, Marcel duchamp wrote:

>> Apparently RED leds are a big no-no on commercial equipment;
>
> Bill, could you elaborate on that one?
> Was that tongue-in-cheek or serious?
>
Serious, although I don't know the details. At some point there
was a real fire-drill here to eliminate the use of red LEDs; I suspect
some telco or european standard that reserves red for truly "critical"
notifications. I'll see if I can find out...

BillW

2006\11\27@182358 by Richard Prosser

picon face
We've had to restrict the use of red leds so that they are only used
to indicate a fail or alarm condition. Using them for power-on
indication is a definate no-no. I'm not sure which market it came from
- possibly Europe.

Richard P

On 28/11/06, alan smith <.....micro_eng2KILLspamspam.....yahoo.com> wrote:
{Quote hidden}

> -

2006\11\27@194154 by William Chops Westfield

face picon face
> what's wrong with red?
>
Here's some of the "discussion" that ensued.  An interesting combination
of standards, "common sense", typical usage, and urban legend:

> [see] http://eetd.lbl.gov/Controls/publications/1621Note.pdf
>
=====

> I have also heard (but could not find a reference to substantiate)
> that in Germany for service providers the color RED denotes that
> the equipment is on fire ! This is fairly consistent with the
> "emergency condition" mentioned below.

=====

{Quote hidden}

=====


> The theory is to make it easy for craft to take the appropriate action:
> red == replace, yellow == test, green == good.  There is no doubt
> some Telcordia GR on this, but I don't know which one

=====

> We heard a rumor about some rule in the EU that banned a red LED unless
> bodily harm was imminent, but were never able to find the source.
>
> We spoke with a number of Cisco people in EMEA that thought this must
> be
> a joke, and also had one of our compliance engineers look into it - no
> one found anything.
[but this is not so different from the Mil-Spec listed above for
 flashing red]

=====

> I belive it was NEMA standards - red lights mean "ALARM" so a tech can
> quickly identify a device having problems.

Someone also mentioned that typical red/green dual-color LEDs are
particularly difficult to distinguish for the 7% of males who are
color-blind...

BillW

2006\11\27@215446 by Aaron

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alan smith wrote:

{Quote hidden}

I wonder if it has anything to do with red being associated with danger?

We are currently building a bunch of industrial machinery bound for
China.  The Italian engineering company that wrote the spec says that
all push buttons for the motor starters are supposed to be green for
stop and red for start.  Pilot lights are to be red for running and
green for stopped.  Just backwards from the way most of the equipment we
build for use in the USA...

Aaron

2006\11\28@001057 by Mike Hord

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Well, lots of speculation about limited allowance of red LEDs, and
that may be the deal.  I spoke to an optical engineer friend of mine
and while he admits that he has no specific expertise in it, he
couldn't think of a good reason, either.  Since these things are
marketed as being for outdoor signs where they would form discrete
pixels, I guess it's possible.  It's just odd that of all the "sets" of
LEDs, only this one had all four colors.

Ah well.  I have some extra orange LEDs now.  I have a project for
them, too.  ;-)

Mike H.

2006\11\28@012204 by Jake Anderson

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>
>
> I wonder if it has anything to do with red being associated with danger?
>
> We are currently building a bunch of industrial machinery bound for
> China.  The Italian engineering company that wrote the spec says that
> all push buttons for the motor starters are supposed to be green for
> stop and red for start.  Pilot lights are to be red for running and
> green for stopped.  Just backwards from the way most of the equipment we
> build for use in the USA...
>
> Aaron
>  

It does make sense though.
If red means danger and green means safe.
Pressing the red button makes the thing dangerous (ie running) press the
green button to make it safe.

Western way is red = stop, green = go danger doesn't come into it.


2006\11\28@022114 by Richard Prosser

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And when did Italy move East - Oh - maybe the spec requirement came
from China? But I'm in Shanghai right now and the engineers here say
that the emergency stop buttons are always red. It's a bit hard to
find out more about the led colours but the equipment here only has
green leds showing. On the ATE displays a green colour is used for a
pass and red is used for a fail FWIW.

RP

On 28/11/06, Jake Anderson <@spam@jakeKILLspamspamvapourforge.com> wrote:
{Quote hidden}

> -

2006\11\28@042926 by Alan B. Pearce

face picon face
>Apparently RED leds are a big no-no on commercial equipment;
>perhaps the OGB selection is for that sort of application?

This may be due to CE certification, and similar rules elsewhere. I did a
unit that used a red neon indicator as a power indicator, and had to change
it to a green LED to get by the certification fellow who was checking for
CE.

Red must only be used for an emergency alarm AIUI.

2006\11\28@045133 by Alan B. Pearce

face picon face
>We are currently building a bunch of industrial machinery bound for
>China.  The Italian engineering company that wrote the spec says that
>all push buttons for the motor starters are supposed to be green for
>stop and red for start.  Pilot lights are to be red for running and
>green for stopped.  Just backwards from the way most of the equipment we
>build for use in the USA...

This is actually the same way around as traffic lights.

Think of the colours in these terms -

green - safe for humans to get involved, safe to proceed (traffic light)

red - dangerous equipment in operation, danger ahead (traffic light)

So when you press the red button you are making the equipment an unsafe
environment.

When you press the green button you are making the equipment a safe
environment.

The Italians have had things this way around for a long time, and when you
think about it being like traffic lights it makes sense.

2006\11\28@053045 by Tony Smith

picon face
> >Apparently RED leds are a big no-no on commercial equipment; perhaps
> >the OGB selection is for that sort of application?
>
> This may be due to CE certification, and similar rules
> elsewhere. I did a unit that used a red neon indicator as a
> power indicator, and had to change it to a green LED to get
> by the certification fellow who was checking for CE.
>
> Red must only be used for an emergency alarm AIUI.


Maybe that explains the popularity of blue LEDs.  Still, it's pretty cool
that you can get green neons (& other colours) these days.  Is that what you
used?

Tony

2006\11\28@070027 by Gerhard Fiedler

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Alden Hart wrote:

> It's also worth noting that they tend to use 16 bit controls on the PWM
> for dimming. It seems that fewer bits than this (i.e. less temporal
> resolution in the pulses) gives you visible steps (quantization errors)
> at low light levels.

If you had a log scaled PWM generator, fewer bits would be fine -- most are
not, but it's not impossible, depending on the technology used.

Gerhard

2006\11\28@073924 by Alan B. Pearce

face picon face
>Maybe that explains the popularity of blue LEDs.

I was told by my Keithley rep that the 2400 sourcemeter originally had a red
LED for "output on", but they had to change it, and ended up with a blue
one.

>Still, it's pretty cool that you can get green neons
>(& other colours) these days.  Is that what you used?

No, I couldn't bet a suitable neon, so ended up using an LED. I wasn't going
to go to a lot of trouble, as we were making only 2 units. I just wanted an
indicator that showed the mains was on if the switchmode supply went belly
up, or a lack of it if a fuse blew. Result was some distributed resistors to
drop mains to LED voltage.

2006\11\28@074640 by Mike Harrison

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On Tue, 28 Nov 2006 09:59:37 -0200, you wrote:

>Alden Hart wrote:
>
>> It's also worth noting that they tend to use 16 bit controls on the PWM
>> for dimming. It seems that fewer bits than this (i.e. less temporal
>> resolution in the pulses) gives you visible steps (quantization errors)
>> at low light levels.
>
>If you had a log scaled PWM generator, fewer bits would be fine -- most are
>not, but it's not impossible, depending on the technology used.
>
>Gerhard

You generally need a minimum of 12 bits, mostly to cope with nonlinearity at low levels - you can
take a 256 level value and put it through a linearising table to give a 12 bit PWM value to get a
nice smooth fade.

2006\11\28@075419 by Alden Hart

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Gerhard Fiedler wrote:
> Alden Hart wrote:
>
>  
>> It's also worth noting that they tend to use 16 bit controls on the PWM
>> for dimming. It seems that fewer bits than this (i.e. less temporal
>> resolution in the pulses) gives you visible steps (quantization errors)
>> at low light levels.
>>    
>
> If you had a log scaled PWM generator, fewer bits would be fine -- most are
> not, but it's not impossible, depending on the technology used.
>
> Gerhard
>
>  
Agreed. It's a good idea. A log function would actually be preferable as
the lighting level is not evenly distributed across the entire dimming
range.

I have actually used a mapping table to create a non-linear transfer,
but the underlying problem is the resolution of the pulse widths
themselves, and what degree of granularity you can control. For example,
a 120 hz cycle clock gives 8.33... MS per cycle, which is about 32+ uSec
per width increment at 8 bits. Doable for multiple channels with a
medium sized PIC. Going to 16 bits takes the pulse resolution down to
the 100+ Nsec range - much harder if not impossible (<1 instruction
cycle at 20 Mhz). You could use the PWM generators on chip, but then you
are limited to 2 control channels - unless you can figure out some
clever way to multiplex them.

The good news is that this problem only shows up at very low levels
(first 6 - 10 steps), and is only visible at very slow fades (e.g.
fade-to-black over 10 seconds). You can see this effect in some of the
newer LED signs if you watch closely. Evidently the effect is
distracting enough that serious architectural and stage controllers use
higher resolution PWM.

Alden

2006\11\28@082435 by Alan B. Pearce

face picon face
>Agreed. It's a good idea. A log function would actually be
>preferable as the lighting level is not evenly distributed
>across the entire dimming range.

A u-law or A-law telephony converter comes to mind.

2006\11\28@082536 by Mike Harrison

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On Tue, 28 Nov 2006 07:54:16 -0500, you wrote:

{Quote hidden}

Yes, there is a really neat way to increase resolution without increasing clock.
for each PWM cycle ( say 120hz) :
 You first do all 8 channels in parallel with 32us/step
 You then do one pulse of 0..31.5us ( on 8MHz PIC) on each channel in turn.
This gives you another 5 bits of control at the same refresh rate.
The only caveat is that your drivers can switch sufficiently fast. No problem for smaller setups but
gets to be an issue whne you are driving big FETs for big LEDs.



2006\11\28@085506 by Alan B. Pearce

face picon face
>>Agreed. It's a good idea. A log function would actually be
>>preferable as the lighting level is not evenly distributed
>>across the entire dimming range.
>
>A u-law or A-law telephony converter comes to mind.

Having said that I went investigating, after realising that such a DAC or
ADC isn't going to give PWM results.

Via http://en.wikipedia.org/wiki/Mu-law_algorithm found this
http://hazelware.luggle.com/tutorials/mulawcompression.html which gives some
C source code for doing both A and u-law. Don't know that it really helps
the OP though.

2006\11\28@102041 by Robert Ammerman

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My eyes are assuredly not the best, but I once built a three phase dimming
control system (don't ask) which broke each 1/2 into 768 steps (3*256). This
seemed to be enough resolution to avoid discernable step-by-step changes in
light intensity across the entire range, including the low end.

Bob Ammerman
RAm Systems


{Original Message removed}

2006\11\28@115956 by Alden Hart

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Robert Ammerman wrote:
> My eyes are assuredly not the best, but I once built a three phase dimming
> control system (don't ask) which broke each 1/2 into 768 steps (3*256). This
> seemed to be enough resolution to avoid discernable step-by-step changes in
> light intensity across the entire range, including the low end.
>  
I have seen incandescent dimmer systems work well down to 100 steps -
some of the early digital dimming consoles worked like this. It's the
LEDs that create the challenges at the low levels because they have no
"fade" to smear the steps.

Alden
> Bob Ammerman
> RAm Systems
>
>
> {Original Message removed}

2006\11\28@123259 by Peter Krengel

picon face
RGB color mixing is simple using any µC. Simply use PWM (Pulse width
modulation). LEDs are then driven by 3 outputs giving the LEDs pulses with
variable width. Using delay loops you may vary the pulse width without any
visible steps from 0 to 100%. The smaller the pulse (i.e. 1µs) the darker
the LED(s).

Peter



{Original Message removed}

2006\11\28@151903 by Herbert Graf

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On Tue, 2006-11-28 at 09:51 +0000, Alan B. Pearce wrote:
{Quote hidden}

But using your traffic light analogy it can easily go the other way:

traffic light green means "go" -> make the machine go
traffic light red means "STOP" -> make the machine stop

Neither is more "right" then the other, it's all about the cultural
background of the person pushing the button.

It is kinda scary that what means "safe" to one person means something
the EXACT opposite to another.

TTYL

2006\11\28@155316 by Andre Abelian

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and yellow means you can ether go or stop.
just kidding.
as far as red color goes welcome to America every thing
is business. I made a few products that only red led is used
and when it is on "no blink" it means it is working as power led when it
starts blinking it gives error code and they know there is
a problem and they look at error code.
It will be nice to use green as power led but then the price will go up.

Andre


{Original Message removed}

2006\11\29@054407 by Gerhard Fiedler

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Mike Harrison wrote:

> On Tue, 28 Nov 2006 09:59:37 -0200, you wrote:
>
>>Alden Hart wrote:
>>
>>> It's also worth noting that they tend to use 16 bit controls on the PWM
>>> for dimming. It seems that fewer bits than this (i.e. less temporal
>>> resolution in the pulses) gives you visible steps (quantization
>>> errors) at low light levels.
>>
>> If you had a log scaled PWM generator, fewer bits would be fine -- most
>> are not, but it's not impossible, depending on the technology used.
>
> You generally need a minimum of 12 bits, mostly to cope with
> nonlinearity at low levels - you can take a 256 level value and put it
> through a linearising table to give a 12 bit PWM value to get a nice
> smooth fade.

That's why I said "a log scaled PWM generator". I meant a hardware circuit
that translates eg. 256 linear steps of voltage or time into 256 log scaled
steps of time. For example by using a capacitor (dis)charging function.

Gerhard

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