LED flashlight for hunting

[JimmyM]

I looking into building a tracking light for a friend. There are a few flashlights out there that use a combination of blue and red LEDs. Hemoglobin absorbs strongly in the blue band (410-420nm) and transmits strongly in the red (680-690nm). So if 2 colors of light are used. The background will transmit and absorb both colors to varying degrees, but the blood will show up as bright red on a bluish purple background. Since there's no green light. chlorophyll won't have much to work on and its green color will be muted.
OK enough with the preamble.
I was thinking of modding an existing light (one of those cheap 40+ 5mm LED array flashlights) but thought I could use a triple LED reflector and diffuser lens.
Thoughts of where I might get the parts for a triple LED (Cree probably) LED light?

 

[OKWalker]

Have you considered one of these?

http://www.candlepowerforums.com/vb/showthread.php?t=258404

 

[ti-force]

Or modding two lights like these - Clicky

 

[wyager]

410-420nm is NOT blue-it is dark purple. 405nm is at the very end of human perception and is very dim. Around 470nm is the blue of this smiley face-:nana:-maybe this smiley is closer to 480nm. The quark RGB will probably be around the 450nm range at the lowest, but I would think it would still work well.

 

[ti-force]

I've heard mixed results about blood lights. I actually modified both of my Quarks to try it out, but mostly I wanted a red light for walking in and out of the swamp/woods during the dark. Red light won't disturb game animals as much as white light, plus it will help preserve my night vision. I'd like to buy some cow blood from my local butcher (could you imagine the looks they would give me when I asked for that oo:), and actually try out the red and blue together to see if it actually makes any difference, but I really don't have enough spare time at the moment to devote towards doing a proper test; the testing would need to be done on different types of fallen foliage, as well as grass or whatever type of ground cover exists in your area during the months the hunting takes place. Dry blood vs wet blood, etc., etc.

The emitter I used in my blue Quark is in the 450-465nm range according to the datasheet.

 

[JimmyM]

Good suggestions all.
I looked at Crees, their wave lengths are not as close to what I'd like to use. 5mm types have a far better selection of wavelengths. The 420nm LEDs are deep purple, not blue as stated above. They may be too purple to use.
Red Crees are also 620-630nm. I'd like to find Reds in the 660 range if I could. The absorption curve for Red is quite steep in that area, so 30-40nm may make a difference. I'm also comparing the absorption spectra if chlorophyll and carotenoids (both plant pigments). Still working on that. I'm trying to find LEDs that don't light up the red end of the chlorophyll or carotenoids.
As an experiment I may just try using a bunch of cheapie red and blue LEDs I have and see what happens.
Yeah. Getting come cow's or pig's blood is not really on my "really want to do" list. I may end up on someone's Watch List.

 

[wyager]

Do you want plants to appear dark, or light?

 

[JimmyM]

Thanks, wyager. I had found similar graphs elsewhere as well.
I've been looking up absorption spectra for hemoglobin, chlorophyll, and carotenoids.

All seem to absorb blue, but carotenoids transmit broadly but not too strongly in the red end. They're only visible when chlorophyll is dead (fall leaves). Oxygenated hemoglobin transmits very strongly in the 660-680nm range.
For a test, I'm using a cheapo 15 LED UV flashlight, but am replacing the center 3 LEDs with red ones. The cheapo UV LEDs emit in the 395-420nm range. That's why they look so purple. Good UV LEDs have shorter wavelengths. The Reds I have are in the 620-630 range but hemoglobin also transmits well there too. Just not as good as at 660-680nm. If my friend's tests go even remotely well, I'll get more closely selected LEDs to target the wavelengths better. Testing will be done in the dark/twilight times. For better lit times, a powerful 650nm LED would be good to boost the light from the hemoglobin. Can't do much about the other wavelengths since they're coming from daylight.

 

[HeyGuysWatchThis]

I'm definitely interested, because I have been given the same request by a coworker, also. I'll be following this thread avidly

 

[Pacecar]

Dried blood will be seen differently than wet blood.

 

[ti-force]

Dried blood will be seen differently than wet blood.

Yes, and in a perfect world we wouldn't have to worry about that, but we all know we're far from that. This is one reason why I think it would be best to get some blood, and test before taking the light out into the field where it matters.

 

[Incan]

red/blue blood tracking lights do not work

 

[JimmyM]

red/blue blood tracking lights do not work

Care to expand that statement?
Do you have personal experience? What was that experience?
Do you know of a type that does? Which one have you tried? Were they just red/blue or specific red/blue wave lengths.
You can't just simply make that statement and expect to have it carry weight.

 

[JimmyM]

Dried blood will be seen differently than wet blood.

Certainly. This project is to help increase the contrast of fresh blood in low light conditions. Do I expect it to show up as a bright fluorescent red trail on a black and white background? No. Just to help smaller fresh trails be more easily seen in low light.

 

[HeyGuysWatchThis]

So, any update on that project? Bow season is rapidly approaching...

 

[JimmyM]

I have a cheapie UV light that uses an array of 5mm LEDs. They're rather purple. So I replaced the center 3 with red LEDs and added a resistor so they run at ~22mA ea with 3 AAA batteries. The red LEDs are most likely in the 620-630 nm range (most common). So it's not perfect. I'm delivering it to my friend this week. It's just a proof of concept. If he thinks it improves contrast at close range, I'll get a bigger LED array type flashlight head and make one that uses the proper 430nm/660nm LEDs.

 

[cnjl3]

I bowhunt and for me the best light is a good bright incandescant. I use my Surefire M6 a lot. But one year I left my M6 in my camphouse and I used an Aleph A19 XR E Cree and was surprised how easily I was able to follow a blood trail about 25 yards. I went back later to compare "beams" and the M6 easily beat the A19 XR E Cree when doing a side by side comparison.

 

[JimmyM]

That's interesting. Especially since white LEDs typically have less red spectrum.
Thanks for the feedback.

 

[ti-force]

JimmyM,

I know this thread has aged some since I last checked it, but was your proof of concept light (that you delivered to your friend) successful enough for you to build one using led's that emit more application specific wavelengths of light?

Thanks!

 

[CarbonCop]

I too am interested to hear what you learned. I have had two instances in the past three years that a "properly tuned" tracking light would have been incredibly valuable and am trying to find one before the season starts this year (October 1st).

Thanks!
sds