Discharge in white LED??

[I.N. Galidakis]

After looking carefully at the Nichia-type cheap bright white LED whose spectrum
was added to my web page lately, I projected the beam against a white wall and
can discern a mini purple/blue discharge at the center and yellow fluorescence
around it.

My question about these LEDs now is: Is there an actual "discharge" taking place
at the very center of this LED?

The reason I am asking is because in older LEDs I examined the core long time
ago and could see only a very thin wire connecting the diode electrodes.

On this LED, when I point it at the wall, I see a very faint discharge. Are my
eyes playing tricks or is there an actual discharge taking place there?

Thanks,
--
Ioannis

[Victor Roberts]

Is this the real Ioannis?

There are no discharges (as we know them) inside LEDs.

The LED chip projects a narrow blue beam. Some of this
comes right through the phosphor, while the rest of the
light is scattered, absorbed, and reemitted at various
longer wavelengths. This probably accounts for the spot of
bluish light that you see when the beam is projected on the
wall.

--
Vic Roberts
http://www.RobertsResearchInc.com
http://www.cflfacts.com
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[I.N. Galidakis]

Victor Roberts wrote:
> On Sun, 11 Oct 2009 01:40:30 +0300, "I.N. Galidakis"
> <morp...@olympus.mons> wrote:
>
>> After looking carefully at the Nichia-type cheap bright white LED whose
>> spectrum was added to my web page lately, I projected the beam against a
>> white wall and can discern a mini purple/blue discharge at the center and
>> yellow fluorescence around it.
>>
>> My question about these LEDs now is: Is there an actual "discharge" taking
>> place at the very center of this LED?
>>
>> The reason I am asking is because in older LEDs I examined the core long time
>> ago and could see only a very thin wire connecting the diode electrodes.
>>
>> On this LED, when I point it at the wall, I see a very faint discharge. Are
>> my eyes playing tricks or is there an actual discharge taking place there?
>>
>> Thanks,
>
>
> Is this the real Ioannis?

Of course. I don't know whatever gave you the idea that just because I happen to
know a couple of things about lamps, I also, automatically understand p-n-p
junctions or their operation. I am very far behind on LED basics. I need to do
more homework :-)

> There are no discharges (as we know them) inside LEDs.
>
> The LED chip projects a narrow blue beam. Some of this
> comes right through the phosphor, while the rest of the
> light is scattered, absorbed, and reemitted at various
> longer wavelengths. This probably accounts for the spot of
> bluish light that you see when the beam is projected on the
> wall.

So the difference seems to be that in classic discharges we have plasma emitting
photons, while on diode junctions we have solid matter emitting photons?

Is that why you say "no discharges (as we know them)?

Thanks,
--
Ioannis

[Victor Roberts]

On Sun, 11 Oct 2009 06:40:46 +0300, "I.N. Galidakis"
<morp...@olympus.mons> wrote:

In a light emitting diode, photons are emitted from the
junction between the P-type and N-type material. I didn't
want to get into a battle of words with some person who felt
that the free electrons and holes in this region constituted
a "discharge."

[I.N. Galidakis]

Victor Roberts wrote:
[snip]

> In a light emitting diode, photons are emitted from the
> junction between the P-type and N-type material. I didn't
> want to get into a battle of words with some person who felt
> that the free electrons and holes in this region constituted
> a "discharge."

Sorry for the confusion. The way I understand it, seems that the only difference
between a "classic" discharge and what happens in a LED, is the "medium" inside
which the electrons bounce around. In a classic discharge they bounce around in
plasma. In a LED they seem to be bouncing around in solid matter. In both cases,
photons are emitted. Hence my strange terminology in terms of "discharge".
--
Ioannis

[Don Klipstein]

There is no discharge. The blue is from the blue LED chip. The area of
glowing phosphor may be larger than the chip, with the central portion of
a mound of phosphor showing light that is more bluish than surrounding
areas. The phosphor may cover the chip unevenly in some cheaper LEDs,
leading to a small especially bluish spot or streak.

BTW, most blue LED chips have nondonductive substrates (artificial
sapphire), and have 2 wires going to the chip. Sometimes the connections
leave an odd-shaped area of the chip exposed.

- Don Klipstein (d...@misty.com)

[TKM]

"Don Klipstein" <d...@manx.misty.com> wrote in message
news:slrnhd730...@manx.misty.com...

Remember too that blue wavelengths of light are not handled well in the eye
from the optical standpoint. Blue light sources, for example, appear
optically larger than they are physically.

Terry McGowan