[Laser] Light Communications Questions

Dave wa4qal at ix.netcom.com
Tue Mar 3 13:14:21 EST 2009


laser-request at mailman.qth.net wrote:

> Message: 1
> Date: Tue, 03 Mar 2009 09:29:14 -0500
> From: Stan <stan at capecod.com>
> Subject: [Laser] Light Communications Questions.
> To: laser at mailman.qth.net
> Message-ID: <49AD3EBA.4090706 at capecod.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> Hello The Net:
> 
> I have accumulated some questions:
> 
> 1. Looks like power LEDs are advancing nicely, with respect to actual 
> light power output (lumens).

Yes.

> Any thoughts as to the applicability to light communications ?

Should work quite well.  Chris Long and team appear to have done quite a
bit of work with them:

http://www.bluehaze.com.au/modlight/Luxeon.htm

Including setting a 104 mile distance record with an LED:

http://www.bluehaze.com.au/modlight/index.html

> I just got in a 5W ( 3 x AAA batteries) flashlight and it looks like the 
> single LED is fed DC power directly from the battery bank. No driver module. 

Are you sure that it doesn't have an integrated driver?  Or, are they
counting on the internal resistance of the batteries to limit the
current?

> No idea how many lumens it puts out.

I see that some of the Philips Luxeon LEDs put out up to about 140
lumens.

http://www.philipslumileds.com/products/luxeon/luxeonK2

> Colored filters (band pass filters) are not commonly available for it yet.

Rather than filtering a white LED, it should be quite beneficial to
generate the colour you want directly.  Note that the Luxeon LEDs
are made to produce different colours.

http://www.philipslumileds.com/products/luxeon/luxeonK2

> Ebay also has listing for a 12W, single LED, flashlight, using 2 each 
> CR123A ( 3.7V @ 1000 mAh)  batteries.

Impressive.

> 2. Any idea what the band pass of the Kodak red wratten sheet filter 
> material is ?
>  Yes red, but 627 or 635 nM ?  or 600 or 7000 nM,  half power bandwidth ?

I remember seeing the band pass characteristics for Wratten filters in
an old edition of the Handbook of Chemistry and Physics.  I think that
table has been dropped from recent editions, though.  As best as I
remember, they were rather broad-banded.

> 3. Any know issues with modulating the higher power LED sources ?

I'm not sure if the temperature cycling would be a concern or not.

> Can they handle 10 MHz modulation or is there severely limited
> frequency response due to the actual (large) die construction ?

I don't know that I've heard anyone trying.  It should be easy enough
to test, though.

> I have seen current sourcing "dimmable"  drivers, but I expect the 
> frequency to be in the low audio range.

Probably more likely in the upper audio range (to minimize component
size, flicker, etc.).

> 4. I am looking for a source of larger acrylic fresnel lenses.
> At one time this reflector pointed me to a Asian source, but I have lost 
> the reference.

Have you checked Edmund Scientific?

http://scientificsonline.com/Default.asp?

I remember picking up some page sized (8.5"x11") fresnels
from a "dollar" store in western Canada a few years ago.

> I am still in the thinking stage.

Thinking is good.  :-)

> Thanks for the assistance,
> Stan, W1LE    FN41sr   Cape Cod

Dave
WA4QAL



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