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#45318 - 07/31/05 02:10 PM Re: soft red glow light, Re: Seeing at night 2 of
AyersTG Offline
Veteran

Registered: 12/10/01
Posts: 1272
Loc: Upper Mississippi River Valley...
Ironsraven,

Cool idea, making a low intensity red - thanks. There's an unused Solitaire in the log base here somewhere... anyway, your idea gives me another idea along those lines (low intensity red).

I can offer you a tip about the smoked yellow LED: You need a resistor in the circuit. Coin cell batteries like you got from the little 12v MN21 work OK without a limiting resistor because as soon as the LED tries to draw enough current to fry itself, the internal resistance of the battery shoots up - they cannot deliver much current. But AA batteries have the capability to deliver far more current than it takes to fry a 5mm LED. Check the specs on that yellow LED and you'll see it probably has a rated Vf of 2.xxx volts. Two AA in series give you ~3 volts. And the LED has a max rated current - probably about 20ma or maybe 30ma if it's a super bright.

Really really simple math to figure out what size resistor to stick in there and if you do it using an insulating disk to hold the resistor between the batteries (or between the battery stack and either end), it's trivial to pull the resistor and LED and then drop the bulb back in. A resistor automatically means that your circuit efficiency is reduced because you're bleeding some power into heat, but over-all it's a tiny amount of power anyway, so run-time should be really generous - I'm guessing well over 100 hours on two AA - maybe far more than that. Rather than re-hash all the how-to, there's plenty of help on this on the 'net (or surf CPF). Even on and off-line calculators for this.

You might get away with a green in the 2 x AA because IIRC, they want something in the neighborhood of 3.6 volts - anyway, over 3 volts. So it might light up VERY faintly, with extremely low current draw, direct-connecting it to two AA in series - have not tried it myself, but it may work. A 5mm would give a little more light, but you would have to mod either the reflector or the LED package to fit it in a minimag.

Thanks for the low-intensity red idea!

Tom


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#45319 - 07/31/05 02:36 PM Re: soft red glow light, Re: Seeing at night 2 of
brian Offline
Veteran

Registered: 07/28/04
Posts: 1468
Loc: Texas
Those are both really cool ideas. I think I have a Mag Solitaire laying around here too somewhere.
_________________________
Learn to improvise everything.

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#45320 - 07/31/05 07:03 PM Re: Traveling at night
widget Offline
Addict

Registered: 07/06/03
Posts: 550
The desert is surely a place for night travel in the summer, if you must walk somewhere. Seeing is not always that hard, once your eyes adjust to the dark.
It was pretty common in the military to have to move at night, without night vision equipment. Tactically, it is safer although night vision, FLIR and thermal imaging make it less desireable. One thing to consider is that few soldiers have night vision equipment, often do not use it on the move because of depth perception problems and some sensors can be overcome by resoucefulness. We once hid successfully from an AC-130 gunship while on a training mission. It did not take much. However, as the AC-130 crew said later, if we had fired on you, even though we did not see you, you would likely gotten up and ran!
Anyway, night travel may not always be desired but in an emergency may be a necessity. Having a good light source and navigation aids, along with the ability to travel in darkness, is a good skill to aquire.
_________________________
No, I am not Bear Grylls, but I stayed at a Holiday Inn Express last night and Bear was there too!

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#45321 - 07/31/05 10:10 PM Re: soft red glow light, Re: Seeing at night 2 of
Anonymous
Unregistered


That's the problem with radioshak components- no data sheets. I didn't feel like trying to figure out a big enough digikey or jameco order to make it worth while. Still haven't, that's why I have tried this trick with a better LED. I'm sure I could go and snitch one from the supply closet, but why bother? I really wanted it for the red any way.

I was pretty sure that it was a question of amperage. I'm just not ambitious enough on this project to figure out what size of a resistor I need in the circuit *humming nursery rhymes* Twinkle, twinkle, little star, power equals eye-squared are. :P

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#45322 - 08/01/05 01:32 AM Re: Traveling at night
lazermonkey Offline
Enthusiast

Registered: 12/27/04
Posts: 318
Loc: Monterey CA
I have heard the same thing about night vision and eye color. I have read some on the subject in anatomy class. I look for my notes.
_________________________
Hmmm... I think it is time for a bigger hammer.

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#45323 - 08/01/05 03:16 AM Re: soft red glow light, Re: Seeing at night 2 of
AyersTG Offline
Veteran

Registered: 12/10/01
Posts: 1272
Loc: Upper Mississippi River Valley...
Just a shot in the dark, but typical data for a TRS 3mm Red looks like 2.25v - 2.6v at 28ma max. Feeding it 3v, try a 33 ohm 1/8 watt resistor. For a 5mm yellow run-of-the-mill, 2.15v to 2.6v Imax 36ma - try a 22 ohm 1/8 watt resistor. I figured them at 2.3v across the LED and 25 ma for red and 35 ma yellow, closest standard resistors, and 1/8 watt is the standard little TRS resistor power rating, which is more than large enough. You can fiddle with the numbers - here is a link to a calculator. I think I was wrong about the green LED Vf - looks like most of them are in the range of the red and yellow and the cheapies take VERY little amperage.

HTH,

Tom

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#45324 - 08/01/05 03:24 AM Re: Traveling at night
AyersTG Offline
Veteran

Registered: 12/10/01
Posts: 1272
Loc: Upper Mississippi River Valley...
Caleb,

Thanks - whatever you find, please let us know. It would be very cool if you had a source data cite, but some info beats none.

Regards,

Tom

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#45325 - 08/01/05 05:43 AM Re: Traveling at night
lazermonkey Offline
Enthusiast

Registered: 12/27/04
Posts: 318
Loc: Monterey CA
From what I can recall the color of the eye has little if any effect on you ability to see at night. The correlation is dark eyed people happen to have more rods (light sensitive part) than light eyed people. Light eye people have more cones (color sensitive part) than Dark eyed people. In a nut shell Dark eyes usually indicates better night vision. Light eye indicates better color distinction. None of this is absolute there are light eyes with great night vision and dark eyes with great color distinction. And there are the super freaks with great eyes altogether. <img src="/images/graemlins/shocked.gif" alt="" />

P.S. Let me know if you have any questions or conflicting information.
_________________________
Hmmm... I think it is time for a bigger hammer.

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#45326 - 08/01/05 05:54 AM Re: soft red glow light, Re: Seeing at night 2 of
JohnN Offline
Old Hand

Registered: 10/10/01
Posts: 966
Loc: Seattle, WA
Quote:
Tom, let me share a bit of technology for what I think might be the ultimate low-dazzle, low-power, home built, functional but kludge looking red light.


Or you could just buy a Gerber Infinity in red.

-john


Edited by JohnN (08/01/05 06:01 AM)

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#45327 - 08/02/05 02:04 AM Re: soft red glow light, Re: Seeing at night 2 of
Anonymous
Unregistered


Two reasons why I'll pass on the offer:

1) This can be converted to run a white incancent bulb in about 2 minutes if you have a spare AAA in your kit. By the same token, if you want to boost the output level, put in an extra battery over the three I mentioned. And you can change colors pretty easily. (ok, that is 1a, 1b, 1c)

2) Solitaire $5
enough batteies for 4 changes <@2
spring ~25 cents
small steel bolt free, easily scrounged
LED about 60 cents through RS
(ouch- you can find them as low a cent in bulk packs)

Less than half the cost. About the cost of the S&H. For Scouts, that is a big facotr. It is also a good project to show kids how to build and modify thier gear better suit thier needs.


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