High power thru-hole LED

[alvin6688]

Hi,

I'm looking for ultra bright thru-hole LEDs for my research, but am new at this whole thing. For my application, I want to place one linear LED array on each side of the forearm and image through the skin layer. I need the light to be powerful enough to go through thick biological tissue while not being harmful. As far as I've learned, heat seems to be the only source of potential danger, so I'm guessing that a heatsink would solve this problem?

Since I have only rudimentary experience with LEDs, what kind of power and/or radiant intensity would you recommend? Currently I'm using an array of fifty 5mm thru-hole 80mW/sr LEDs and its not nearly enough, so I need brighter ones (assuming brightness is the determining factor here).

What are the advantages and disadvantages of thru-hole versus surface-mount? The device is size-sensitive (cost not so much), and I will be hand-soldering the arrays.

Finally, is there any advantage at all of using laser diodes over ultra-bright LEDs? As far as I'm aware, the main differences are collimation and coherence, and neither attribute is relevant here.

Again, I apologize for the beginner questions, and thank you for your time.

-Alvin

 

[LEDAdd1ct]

I would love to see beamshots of this once you get off the ground!

 

[AnAppleSnail]

Do you have any idea how much light you need? I can see large blood vessels with a decent flashlight on my skin. Your eyes glow if you put one in your mouth. There are some very bright LEDs out there, and wire-and-go constant-current drivers. Does color rendering matter?

 

[HarryN]

Hi, I have played with this kind of imaging and it is quite fun.

The absorbtion of most light wavelengths is quite high, so it is useful to concentrate on the 600- 650nm range. LEDs are quite bright around 615 - 620nm, so this is useful.

Surface mount LEDs are much more able to dissipate heat, so that is a good place to look.

To look through your hand, it takes about 5 - 10 K lux. To go through your arm, a bit more, probably something like 100 - 300K lux.

I am not sure that you can be certain that this kind of power level will have no effect without some testing, as it starts to approach power levels that could disrupt cell walls.

 

[fyrstormer]

LED-TECH.de sells 500mW thru-hole LEDs. You'll need to provide some means to connect the wire leads to a heatsink though, if you're going to run them that hard.

Surface-mount LEDs are more efficient, though. Is there a reason you can't use a bunch of them instead?

 

[electromage]

I see an inherent problem with using visible light for this type of imaging. Human tissue (obviously) absorbs quite bit of light, and while it's easy to illuminate soft tissue enough so see surface veins with a moderate light source, it sounds like you're going to need something very bright. The problem with this is that as you increase the amount of visible light on your arm, you also increase the amount of energy that is being absorbed and converted to heat. If you concentrated enough light on your arm to go all the way through, you may cause deep burns.

I also don't think that thru-hole LEDs will be able to produce this kind of light, though there are some very high power (and expensive) LEDs available in a TO-66 package that might be capable.

Then again, I don't think I fully understand what your goal is, and this may all be irrelevant. Something to think about, anyway.

 

[Apollo Cree]

I don't think using a laser gives you any advantages. Laser LEDs are usually less powerful and efficient than visible lasers.

Some of your heat concerns will be less if you design your system to be low duty cycle. i.e. Set things up, press a button, the lights come on for 1 second, you take a picture, then the lights shut off.

Depending on what you're doing, the color of the LEDs may make a big difference. Contrast and penetration will probably be much different for a red LED vs. a blue LED. There might be some "magic" wavelengths that work best. What are you trying to image? Blood vessels, bone, alien abductee tracking devices?

Your best bet may well be a commercial camera strobe light. Be careful the first few times you use it. Some of them might be powerful enough to cause a burn. It's easy enough to buy a strobe and make a quick test.

 

[alvin6688]

Thanks so much for your help! I probably should have been more clear about the application.

We're trying to image veins for a venipuncture-assist device. Many studies have shown that infrared light provides the best balance of light penetration depth and hemoglobin absorption, so I'm looking at the 850-950nm range. 600-650nm is best for the superficial smaller vascular structures, but the large deep veins used for venipuncture require longer wavelengths.

Surface-mount LEDs are more efficient, though. Is there a reason you can't use a bunch of them instead?

The only reason I was hesitant to use surface-mount LEDs was because I have no experience soldering them, whereas I've soldered thru-hole arrays before. But if it's possible to hand-solder SMDs, and if they have better heat dissipation, then they may very well be better than thru-hole.

To look through your hand, it takes about 5 - 10 K lux. To go through your arm, a bit more, probably something like 100 - 300K lux.

Thanks for these numbers, they'll be very helpful. Only thing is, in the IR I can't use lux since it's invisible (and conversion to irradiance is difficult because luminous efficiency of the human eye for IR is zero). Do you have an idea of the irradiance equivalent of 100-300K lux?

Some of your heat concerns will be less if you design your system to be low duty cycle. i.e. Set things up, press a button, the lights come on for 1 second, you take a picture, then the lights shut off.

Yeah we're most likely going to strobe the lights to match the exposure time per frame of the video camera. For 10 frames-per-second acquisition, I can probably get away with a duty cycle under 10%.

Thanks again everyone for helping a newbie out.

 

[-Gast-]

camera strobe light. Be careful the first few times you use it. Some of them might be powerful enough to cause a burn.

Be REALLY careful with strobes...


If you like to take pictures of Blood vessels, infrared would work well, i guess. But you need a camera that captures the ir-spectrum. normal ones have an ir-filter.

 

[alvin6688]

These seem interesting:

http://www.magnalight.com/p-47292-i...-8-3-watt-leds--1440-lumen--850-or-940nm.aspx

They also come in arrays of 12, 16, or more LEDs.

SPECIFICATIONS:
Length: 6.35 inches
Height: 3.25 inches; 5 inches w/ Trunnion Mount
Depth: 3.5 inches
Weight: 3.2lbs
LEDs: 8
Each LED Watts: 3 Watts
Total Watts: 24 Watts
Volts: Operates on 9-42 Volts DC; including 12 and 24 Volts
Amps: 2 amps on 12 volts, 1 amps on 24 volts
Lumens: 1440
IR Wavelength: 850nm or 940nm
Housing Color: black or white available
Ambient operating temperature range: -40 degrees C to 85 degrees C


LUX Measurements (FLOOD):
At The Lens: 185,800
At 1 Meter: 2,672
Lens Temperature: 78 Degrees F


LUX Measurements (SPOT):
At The Lens: 190,400
At 1 Meter: 8,440
Lens Temperature: 77 Degrees F


Only thing is that they don't strobe so it goes to 77 degrees at the lens.

 

[MikeAusC]

For better heat-sinking without needing to surface-mount solder, you could buy 3 watt IR LEDs mounted on aluminium stars.

Just screw them onto your heatsink.

The Dealextreme sku.14061 ones only cost $7. They draw 1.5 amps at 2 volts, but you could under-run them to reduce the heat at each LED.

 

[HarryN]

The key to easy surface mount soldering of LEDs is to use a quality solder paste and a hot plate / heating from underneath.

Modern LEDs usually can take lead free solder temperatures, but I prefer to use lead based solder, especially for proto work. This gives you a much wider margin of error, which is common in hand assy. work.

The nature of solder paste lifetime is that you usually have to buy direct from the mfg or a close knit distributor.

 

[haserman]

Do you have any idea how much light you need? I can see large blood vessels with a decent flashlight on my skin. Your eyes glow if you put one in your mouth. There are some very bright LEDs out there, and wire-and-go constant-current drivers. Does color rendering matter?

i saw the area under my eye _sockets_ glow when i put a bright flashlight in my mouth. how do you get the eye to glow when the whole purpose of the sclera et al is to retain a black environment?

 

[fyrstormer]

i saw the area under my eye _sockets_ glow when i put a bright flashlight in my mouth. how do you get the eye to glow when the whole purpose of the sclera et al is to retain a black environment?

Nothing is perfect. Eyes have never had to deal with bright light coming from *inside* the skull in the middle of the night before. The sclera is good enough to block enough light to keep your vision perceptually glare-free when the light outside the skull is brighter than the light inside, which is all *normal* people ever need.

 

[haserman]

oh, man. this i gotta see. i tried, but i'm not able to get my eyes glowing from the inside. what power light and where did you point it? it would be awesome for halloween.

Nothing is perfect. Eyes have never had to deal with bright light coming from *inside* the skull in the middle of the night before. The sclera is good enough to block enough light to keep your vision perceptually glare-free when the light outside the skull is brighter than the light inside, which is all *normal* people ever need.

 

[bstrickler]

oh, man. this i gotta see. i tried, but i'm not able to get my eyes glowing from the inside. what power light and where did you point it? it would be awesome for halloween.

I've found it works best on leaner people. My eyes glow like bright embers when I did that with my Oveready triple. It also works best with lights that are almost pure flood, rather than a light with a reflector.

https://sphotos.xx.fbcdn.net/hphotos-ash4/206068_10150321868031942_2981520_n.jpg

You could even see most of the veins in my face (this was taken with a camera phone, so you can't see it all that well)! If you're looking at it on an LCD monitor, look at my left eye (the one on the right in the pic), and you'll see several veins.

I need to get another really bright light like that again.

 

[Up All Night]

I've found it works best on leaner people. My eyes glow like bright embers when I did that with my Oveready triple. It also works best with lights that are almost pure flood, rather than a light with a reflector.

https://sphotos.xx.fbcdn.net/hphotos-ash4/206068_10150321868031942_2981520_n.jpg

You could even see most of the veins in my face (this was taken with a camera phone, so you can't see it all that well)! If you're looking at it on an LCD monitor, look at my left eye (the one on the right in the pic), and you'll see several veins.

I need to get another really bright light like that again.

That's an incredible shot from a camera phone, looks like thermal imaging!
How long till the soft palate & tongue become medium rare with that Oveready triple?

 

[haserman]

i got the same result you did with my very bright flashlight. that's just the underside of the eye socket, not the eyeball itself. though i was able to see "light" in my eyes in a dark room when i put the flashlight in my mouth and aimed at its roof. just didn't see light coming out of my eyeballs, pupils or anything else.

I've found it works best on leaner people. My eyes glow like bright embers when I did that with my Oveready triple. It also works best with lights that are almost pure flood, rather than a light with a reflector.

https://sphotos.xx.fbcdn.net/hphotos-ash4/206068_10150321868031942_2981520_n.jpg

You could even see most of the veins in my face (this was taken with a camera phone, so you can't see it all that well)! If you're looking at it on an LCD monitor, look at my left eye (the one on the right in the pic), and you'll see several veins.

I need to get another really bright light like that again.

 

[bstrickler]

i got the same result you did with my very bright flashlight. that's just the underside of the eye socket, not the eyeball itself. though i was able to see "light" in my eyes in a dark room when i put the flashlight in my mouth and aimed at its roof. just didn't see light coming out of my eyeballs, pupils or anything else.

I saw a REALLY bright red light when I did that, and it actually hurt due to how red it was.

That's an incredible shot from a camera phone, looks like thermal imaging!
How long till the soft palate & tongue become medium rare with that Oveready triple?

I only got it to a nice rare before my mouth filled with saliva :laughing: