LED light experimentation

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
mklepper
Posts: 5
Joined: Thu Dec 25, 2008 9:39 am
Contact:

LED light experimentation

Post by mklepper » Thu Dec 25, 2008 2:52 pm

I am a physician with little knowledge in electronics or optoelectronics. I am trying to develope an experimental system that requires a very small profile and volume LED system with as much light intensity as I can get out of it. The requirements are: I want it to fit into the wall of a catheter clear plastic 3mm ID and 5mm OD with a wall thickness of 0.75mm. I need the light to diffuse 360 degree but there is 180 degree aspect that is more "important". I am fiddling with thru hole lights and SMDs too small to work with. I have melted a few trying to solder them looking thru a microscope. (it actually only took one). Any thoughts or suggestions as to where I can get help? Thank you

User avatar
MrAl
Posts: 3862
Joined: Fri Jan 11, 2002 1:01 am
Location: NewJersey
Contact:

Post by MrAl » Thu Dec 25, 2008 3:47 pm

Hello and welcome to the forum...


In order to get that small i think you are stuck with either surface
mount or perhaps a fibre optic solution.

I guess you need white light right? I dont know of any 3mm white
LEDs but i bet they are out there (non SM). The smallest LEDs
i work with are 5mm diameter made by Nichia.

Are these to be inserted into an artery or something like that?


I dont know if this will help but you can look here:
http://www.kingbrightusa.com/gapg1608.a ... GgodohebDg

I found some 3mm LEDs, but they have a narrow view angle:
http://www.jab-tech.com/3mm-White-LED-1 ... -3113.html
LEDs vs Bulbs, LEDs are winning.

User avatar
jwax
Posts: 2205
Joined: Mon Feb 09, 2004 1:01 am
Location: NY
Contact:

Post by jwax » Thu Dec 25, 2008 5:03 pm

Could you clarify the desired light output pattern you seek? I can't tell if you want the light emitting from the end of your tube forward, or to emit othogonal to the tube-out the sides.
Is fiber-optic tubing a possibility as MrAl mentioned?
I'd be glad to help with micro-soldering fabrication.
Also, does the tube have to remain open to fluids, or are there wires and fluids in the tube?
John

mklepper
Posts: 5
Joined: Thu Dec 25, 2008 9:39 am
Contact:

LED system

Post by mklepper » Thu Dec 25, 2008 5:31 pm

I need blue wavelength light. I have some LEDs from Fry's that are T-1 which are around 2mm. The beauty of LED is DC and low voltage and selectable wavelength. I need the light to bathe the space from the vocal cords to the cuff of an endotracheal tube. The space is D shaped 2-2.5 cm and 2-4cm in length. The center of this "space" is occupied by a 10mm clear plastic breathing tube (endotracheal tube). The most important area is the posterior or dependent aspect, the flat part of the D. The carrying device is my invention, the ETS (endotracheal tube sump). I hoped to have the LED series embedded into the wall of the catheter part (3mm ID 5mm OD and 0.75 wall thickness.) Psst... Blue light kills bacteria shhhhh. :-)

User avatar
MrAl
Posts: 3862
Joined: Fri Jan 11, 2002 1:01 am
Location: NewJersey
Contact:

Post by MrAl » Thu Dec 25, 2008 6:52 pm

Hi again,


What kind of intensity are you looking for?

Also, have you considered yet the antibacterial effects of ultraviolet light?
LEDs vs Bulbs, LEDs are winning.

mklepper
Posts: 5
Joined: Thu Dec 25, 2008 9:39 am
Contact:

LED light methods

Post by mklepper » Fri Dec 26, 2008 7:02 am

When I wrote the patent in 1998 I was planning on UV by way of fiber optics. Unfortunately UV causes cancer and there is no way I could ever get that past FDA. Blue light from 400 to 470 kills in a dose dependent fashion (time and intensity). The application allows for continuous exposure if need be. I am starting out by rigging up some various intensity light sources and seeing what various intensities do in the microbiology lab. I have lights from 78 mC to 10,000 millicandela. The 0402 don't make much light at all but I have some Kingbright 2.5X2mm smd rated at 2500 mC at 250 mA. Any experience with conductive epoxy? Does it work, and is it strong?

User avatar
MrAl
Posts: 3862
Joined: Fri Jan 11, 2002 1:01 am
Location: NewJersey
Contact:

Post by MrAl » Fri Dec 26, 2008 7:39 am

Hi again,

That's interesting about the UV and Blue types of light.

I'll mention a few notes just in case you havent thought of these things yet...
if you have then this will be a bit boring to read :smile: but i have no way
of knowing without asking first.

1. Shouldnt you experiment with the quantitative light effect on the bacteria first,
before moving to the design phase, or are you already very confident that this will
work to some degree which will be beneficial?
2. Any LEDs that draw 250ma are going to dissipate a significant amount of
heat. If that heat is not dissipated somewhere the temperature builds up
almost endlessly. I would have to ask therefore what are the heat dissipation
qualities of the human throat, in the exact place you plan to insert this,
or alternately, have you a plan to get rid of this heat?
This aspect of the design depends highly on the outcome of #1 above
because #1 will set the designs target light output which will pretty
much dictate the total heat output that has to be dealt with.
250ma x 3.3v equals 825 milliwatts, a very significant source of heat when
in a confined area. If this were a regular LED design, i would say a 0.825
square inch surface area would dissipate the heat while raising the surface
temperature by about 60 degrees C (acceptable for many solid state devices).
This isnt something you would want to keep your finger on however.
The heat from one smaller LED isnt as bad of course, but for a more significant
amount of light you would need more of these LEDs, and more LEDs put out
more heat.
3. LED lumen maintenance is an issue when running the same LED
for hours on end. The only way to combat this is to perform periodic
tests or, better yet, build in some feedback to trigger an alarm when
the light output decreases to a level which is no longer considered
effective.

I have worked with something similar to conductive epoxy (i assume you mean
electrically conductive rather than thermally conductive). I have to say that
i was surprised by the results, in that the stuff was at least usable, and i was
able to get a rough idea of the resistivity and go from there. It wasnt great
but it was at least usable when soldering isnt going to work.
One note here however is that the resistivity varies *greatly* from product
to product, and so definitely have to check this before buying. Also a
surprise, the resistivity does not necessarily go down with cost, so
a review of the specs is a must. The application technique also varies
the conductivity somewhat too, so the application technique should be
practiced and applied exactly the same way each time, using the same
applied temperature.
Also, a little experimentation before use to make sure the specs are as
they say they are.
I can not comment on the strength however, because the stuff i used was a
very economy version and it didnt even have an epoxy base, but one thing
that helps any 'connection' made with any material like this is the
application of a second coat of some other material that acts as a
protection layer as well as to add strength to the finished joint.
For my needs, i could apply a thick coat of regulator ol' five minute
epoxy and that was all it needed. For your use, you might have to find
a more non toxic material, which im betting you looked into already.

I hope some of this helped, and i wouldnt mind hearing how the whole
thing worked out in the end.


I know this was a little long, so here's a recap of the main points:

1. Quantitative light vs bacteria study / equation
2. Heat dissipation qualities inside the throat; ways to combat
3. Pros and cons of electrically conductive epoxy; strengthening; toxicity; quality testing
4. LED lumen maintenance considerations.
LEDs vs Bulbs, LEDs are winning.

User avatar
dtief
Posts: 59
Joined: Wed Aug 20, 2008 4:13 pm
Contact:

Re: LED light methods

Post by dtief » Fri Dec 26, 2008 5:32 pm

mklepper wrote:The 0402 don't make much light at all but I have some Kingbright 2.5X2mm smd rated at 2500 mC at 250 mA.
That current rating is assuming the case temperature is held within the safe operating area. This will require a heatsink for any length of time over a few seconds, and / or to keep the temperature low enough to avoid burns.

These are not directly what you're looking for but these are some power LEDs I have been experimenting with:
http://home.comcast.net/~davidtief/proj ... /LEDs.html

They are Luxeon K2 emmitters. The blue is running at 4 Watts, about 1 Amp through the LED. I once had one of the LEDs fall off an early test heatsink - it died in seconds. Could you use an LED with fiber optics to get the light to where it is needed?

Dave

User avatar
jwax
Posts: 2205
Joined: Mon Feb 09, 2004 1:01 am
Location: NY
Contact:

Post by jwax » Fri Dec 26, 2008 6:45 pm

Conductive epoxies are a viable bonding method. Some are rated for military as well as space applications, and I'm sure one could be found to meet your requirements.
Are we to assume this LED package is to be bio-compatible with the throat environment of PH, humidity and temperature? That is, all the wiring and LEDs would have to be electrically isolated from the body, correct? Sealing the package from that working environment will be a challenge.
How much time exposure is required? Minutes, hours?
John

mklepper
Posts: 5
Joined: Thu Dec 25, 2008 9:39 am
Contact:

LED

Post by mklepper » Fri Dec 26, 2008 7:34 pm

John and Dave thanks for the ideas. Fiber optics are an option and may be the way I go. Fiber optics require the proper fiber (glass vs plastic) with the proper cladding (or lack of) to allow circumferential diffusion of light at the distal 4-6cm only and a safe and economical method of containing the fiber. I think getting the fiber into the wall of the tubing/catheter will be easy. Figuring out which material and if or how to make it shine the way I need will be trial and error.... Unless you know about this aspect. My other concern on fiber optics was the necessity for a powerful light source, which may be an error on my part. I take it I could "drive" the fiber from the external tip of the catheter with a low voltage (ie battery powered) LED source? The issue of time of illumination is unknown. Some investigators use an on-off cycling device where the light is on for example 1sec and off 2 sec and repeated. I suppose this cycling might get around the temperature buildup? My thought is to encapsulate the light and the wires in the wall of the catheter, which is 0.75mm thick. Not sure but I think this "system" could be extruded into the wall during production.. Again thanks for your time and effort. It helps alot having someone with knowledge and experience in the area give this sort of feedback

User avatar
MrAl
Posts: 3862
Joined: Fri Jan 11, 2002 1:01 am
Location: NewJersey
Contact:

Post by MrAl » Fri Dec 26, 2008 9:12 pm

Glad i could help!
MrAl wrote:Hi again,

That's interesting about the UV and Blue types of light.

I'll mention a few notes just in case you havent thought of these things yet...
if you have then this will be a bit boring to read :smile: but i have no way
of knowing without asking first.

1. Shouldnt you experiment with the quantitative light effect on the bacteria first,
before moving to the design phase, or are you already very confident that this will
work to some degree which will be beneficial?
2. Any LEDs that draw 250ma are going to dissipate a significant amount of
heat. If that heat is not dissipated somewhere the temperature builds up
almost endlessly. I would have to ask therefore what are the heat dissipation
qualities of the human throat, in the exact place you plan to insert this,
or alternately, have you a plan to get rid of this heat?
This aspect of the design depends highly on the outcome of #1 above
because #1 will set the designs target light output which will pretty
much dictate the total heat output that has to be dealt with.
250ma x 3.3v equals 825 milliwatts, a very significant source of heat when
in a confined area. If this were a regular LED design, i would say a 0.825
square inch surface area would dissipate the heat while raising the surface
temperature by about 60 degrees C (acceptable for many solid state devices).
This isnt something you would want to keep your finger on however.
The heat from one smaller LED isnt as bad of course, but for a more significant
amount of light you would need more of these LEDs, and more LEDs put out
more heat.
3. LED lumen maintenance is an issue when running the same LED
for hours on end. The only way to combat this is to perform periodic
tests or, better yet, build in some feedback to trigger an alarm when
the light output decreases to a level which is no longer considered
effective.

I have worked with something similar to conductive epoxy (i assume you mean
electrically conductive rather than thermally conductive). I have to say that
i was surprised by the results, in that the stuff was at least usable, and i was
able to get a rough idea of the resistivity and go from there. It wasnt great
but it was at least usable when soldering isnt going to work.
One note here however is that the resistivity varies *greatly* from product
to product, and so definitely have to check this before buying. Also a
surprise, the resistivity does not necessarily go down with cost, so
a review of the specs is a must. The application technique also varies
the conductivity somewhat too, so the application technique should be
practiced and applied exactly the same way each time, using the same
applied temperature.
Also, a little experimentation before use to make sure the specs are as
they say they are.
I can not comment on the strength however, because the stuff i used was a
very economy version and it didnt even have an epoxy base, but one thing
that helps any 'connection' made with any material like this is the
application of a second coat of some other material that acts as a
protection layer as well as to add strength to the finished joint.
For my needs, i could apply a thick coat of regulator ol' five minute
epoxy and that was all it needed. For your use, you might have to find
a more non toxic material, which im betting you looked into already.

I hope some of this helped, and i wouldnt mind hearing how the whole
thing worked out in the end.


I know this was a little long, so here's a recap of the main points:

1. Quantitative light vs bacteria study / equation
2. Heat dissipation qualities inside the throat; ways to combat
3. Pros and cons of electrically conductive epoxy; strengthening; toxicity; quality testing
4. LED lumen maintenance considerations.
LEDs vs Bulbs, LEDs are winning.

rshayes
Posts: 1286
Joined: Tue Mar 04, 2003 1:01 am
Contact:

Post by rshayes » Sat Dec 27, 2008 12:34 am

I assume that you are talking about the device shown in Pat. No. US 6,460,540. This appears to use an inflatable cuff to trap liquid moving down the trachea and providing a tube for sucking out the trapped liquid. The top of the cuff appears to be an area that would be difficult to drain entirely and thus might be the area that would most promote the growth of bacteria.

One of your illustrations, Fig. 5, shows a ring(12) with ports(14) for draining the area above the cuff. It mighr be possible to embed T1 LEDs in this ring between the ports. This would illuminate the volume between the ring and the cuff as well as the top of the cuff.

Another possibility would be to connect a string of small, surface mount LEDs in series and wrap them in a spiral around the endotracheal tube(30). This would direct the radiation radially outward toward the inside wall of the trachea. A layer of silicone rubber might serve to both hold the LEDs and wiring in place and also provide encapsulation.

The LEDs may be as much as 20 percent efficient. This means that for every watt of light, there must be provision for removing 4 watts of heat. It the power is low enough, and widely distributed, this can probably be transferred to the surrounding tissue. High power in a small area might cause tissue damage. Fractions of a watt of light in a small area might also cause damage.

Mounting the LEDs on the endotracheal tube might be advantageous, since this would allow heat to be carried away by the air flowing through the tube.

If the endotracheal tube walls were made thicker, it might be possible to form tubes within the endotracheal tube wall. Some of these tubes could be used for enclosing the LEDs with the remainder used to drain the sump area. The endotracheal tube diameter would insrease, but the outer surface would be smooth, and only one tube would be required.

User avatar
dtief
Posts: 59
Joined: Wed Aug 20, 2008 4:13 pm
Contact:

Re: LED

Post by dtief » Sat Dec 27, 2008 5:43 pm

mklepper wrote: My other concern on fiber optics was the necessity for a powerful light source

[snip]

on-off cycling device where the light is on for example 1sec and off 2 sec and repeated. I suppose this cycling might get around the temperature buildup?
The K2 Luxeons at 4-5 Watts are very bright. The highest power blue is typical 35 Lumens at 1 amp. 50,000 hour life. They have a whole family of power LEDs & colors. I am most familiar with the K2s.

The size of battery / power supply will be determined by the power level needed, and the time the device needs to operate between charges or replacing the batteries.

At both ends of the fiber optic cable, lenses would be required to direct the light as desired. I know these things exist, but I have not worked with them.

About the heat, the temperature rise is a function of the mass of the assembly, the amount of power and the time it is applied. Using your example, 1s on 2s off equates to 1/3rd of whatever power is delivered. So if you apply 1 Watt 1s on 2s off, it would cause the same temperature rise as .33 Watt continuously. I suppose air or liquid cooling for the internal LED (no fiber optic) version could work, if needed.


Dave

User avatar
Forrest Mims III
Posts: 12
Joined: Thu Dec 18, 2008 6:59 am
Location: Texas
Contact:

Blue Light Source

Post by Forrest Mims III » Sun Dec 28, 2008 7:08 pm

Seems to me that an optical fiber (as suggested above) is a viable solution. Consider that:

1. You can abrade the end of a plastic fiber to cause light to be scattered out the sides of the fiber over any length you chose. Ordinary sand paper or a small file will work.

2. A fiber will allow you to vary the wavelength externally simply by selecting a different LED or even a blue diode laser.

As for the efficacy of blue light in suppressing or killing bacteria, wavelengths approaching the UV will provide better results than blue light. A variety of UV-A LEDs (e.g. 360 nm) are now available that might be ideal for this purpose.

Forrest M. Mims III
www.forrestmims.org
www.twitter.com/fmims

mklepper
Posts: 5
Joined: Thu Dec 25, 2008 9:39 am
Contact:

light

Post by mklepper » Sun Dec 28, 2008 7:27 pm

Forest, UV causes cancer. I am also thinking in terms of volume production of whatever method I end up with. I have some fiber optic materials on the way. Can anyone suggest an economical method of accurately measuring the light intensity at a given distance and direction on my experimental model. It needs to go down to 50 mcd and up to ?

Post Reply

Who is online

Users browsing this forum: No registered users and 32 guests