Pulsating / Flashing LS for self defense

[IsaacHayes]

I got to thinking. Certain frequencies of flashing bright light really mess with you. One time I put a green filter on a strobe light and I couldn't walk straight or anything. I felt dizzy. /ubbthreads/images/graemlins/icon15.gif The police also use such an instrument only using a green laser and optics to make the beam wider and flash it into suspect's eyes so it disrupts their actions. Not only does certain frequencies mess with your thought processes (anyone know which those are?) but imagine the pain of your pupils dialating in and out from brightness, to total darkness, back and forth. /ubbthreads/images/graemlins/eek.gif

So. I'm thinking about building this function into a pewter 2D mag runing on 3C's. Obviously a 5w would be most effective but my light will only be a 1w. So here are my inquires as to what everyone suggest for the best results.

1)<font color="blue">LS color:</font> RB is very hard on the eyes. But would Cyan appear brighter and thus more effective?

2)<font color="blue">Focus:</font> I'm assuming a narrow beam is most effective. Would 30mm optics be best? I'm assuming 1W cyan HD works good with 30mm. Woodbender would know. Don't want too narrow as then aiming it into the attackers face would prove difficult.

3)<font color="blue">Frequency: </font>What frequency should be used? Will a 555 timer and a suitible switching transistor work for a 1W? What about 5Watt?

4)<font color="blue">Switching device:</font> I want to have a swtich so I can go from pulsing to normal on. I'm thinking about using a magnet and a reed switch. Are there any SPDT reed switches out there? /ubbthreads/images/graemlins/icon3.gif (so that when it moves, it stops contact at one side, and starts on another). Or should I use it as a momentary and build some sort of digital flip flop? That would work and any draw from the batteries from it woulnd'nt matter as main power would be stopped from the mag switch anyways.

I look forward to input on this. This could also be used as a great signaling device/attention getter. I'm surprised no one on CPF has made a flashing device yet.

 

[OddOne]

I might can help with #1...

I have all of the available colors of Luxeon in 1-watt power. Of them, the cyan is BY FAR the brightest to the eye, due in large part to the fact that the human eye is most sensitive to roughly thatshade of green.

The syan one produces a strange effect when you get a faceful of it (as fed through a 30mm Fraen narrowbeam optic) - the light ovrewhelms your peripheral vision and makes everything within the field of view difficult to actually see.

oO

 

[IsaacHayes]

I figured Cyan would be the best. Thanks for testing out the colors on your eyes for us /ubbthreads/images/graemlins/smile.gif

 

[JSWrightOC]

As for pulsing circuits, a 555 and a good MOSFET would work great. /ubbthreads/images/graemlins/smile.gif

I am thinking something around 10-15 Hz or less, with a 25% or less duty cycle to give it a stroboscopic effect while maintaining reasonable brightness. Overdriving the LS would be acceptable, considering the lower duty cycle.

I've blinded myself and others with my relatively weak BB400, I would hate to see what one of these in Cyan would do! /ubbthreads/images/graemlins/ooo.gif /ubbthreads/images/graemlins/buttrock.gif

 

[OddOne]

I used a 555 run as a PWM with the duty cycle set to about 10% to push an IRF520 power MOSFET, and through it dropped 750mA into a 1-watt white. (It was bolted to a rather large chunk of aluminum bar stock to deal with the heat.) UNHOLY kind of bright. I oughtta try it with the cyan I have here... /ubbthreads/images/graemlins/grin.gif

oO

 

[IsaacHayes]

JSWrightOC yeah I was thinking low freq like that would cause the best effect. Much higher and you'll just treat it as constant on.

OddOne: PWM? = ? 750ma! wow! will the LS last even though it's being pulsed that still can't be good for it. What was your main power source?
Oh and what is duty cycle?

 

[paulr]

This is all interesting but really, unless the attacker has epilepsy I can't see him/her getting disoriented by an LED whether pulsating or not. Get yourself a Surefire M6 or 10X, both of which were designed for this purpose /ubbthreads/images/graemlins/wink.gif.

 

[IsaacHayes]

Well I want to build it not really for self defence. I had to have an excuse /ubbthreads/images/graemlins/smile.gif I just think flashing bright light would be iritatting/an attention getter/singnaler.

I bet if you used a 5W Cyan and over drived it like OddOne did to his 1W and flashed it, it would sure be evil!

 

[JSWrightOC]

PWM = Pulse Width Modulation. By varying the pulse width (or duty cycle) you can vary the brightness. However, this works best at higher frequencies.

Being able to adjust the duty cycle on a stroboscopic device like this, as well as the frequency, would let you "tweak" it so that it appears most annoying. This, however, will probably be different for different people.

Driving a 1W at 750mA might be relatively safe, considering that people have driven 1W units at this rate continuously before, with adequate heatsinking. A 1W unit driven at 750mA at 10% should not dissipate much more heat than if it were being driven continuously for 75mA, actually. The average light output may not be the same as a 1W driven at 75mA, but the total power dissipation must be the same, following the law of conservation of energy. I don't know if it would be safe to operate with no heatsinking whatsoever, though.

The biggest concern when pulsing any kind of LED like this is the absolute peak current through the bond wires, which are likely the first thing to go when the LED is driven too hard.

 

[arioch]

paulr:

If I recall correctly, a couple of years back, there was a Japanese anime show that showed a pulsing strobe at the end of an episode. A significant number of kids reportedly became nauseous, and some of them were sent into epileptic-like seizures. The episode was reportedly pulled. It seems that there might be something to the use of pulsing/strobing lights for self defense, although since it doesn't appear to affect people on a reliable basis, I'm not sure I would be trusting it with my safety. /ubbthreads/images/graemlins/poke2.gif /ubbthreads/images/graemlins/twak.gif /ubbthreads/images/graemlins/grin.gif

 

[IsaacHayes]

How does PWM tie in with freq? Would say 20hz be the freq, and PWM be the duration it is on in relation to how long it's off? like 10% pwm is 10% on longer than it's off??

 

[JSWrightOC]

PWM refers more to the actual modulation (changing of) the pulse width, whereas a fixed "10%" would be referred to as a duty cycle. That means that the output is on 10% of the time, off 90%, occuring at whatever frequency you operate it at.

At 20Hz 10% duty cycle, that means that each period lasts 50mS...of that 50mS, the output is on for 5mS (10% of 50mS) and off for 45mS (90% of 50mS).

I hope this doesn't sound too confusing. /ubbthreads/images/graemlins/smile.gif

 

[IsaacHayes]

ok got ya I belive. so with a 10% duty cycle at 1hz, the light would be on for .1 of second, while being off for the remaining .9. It would apear to just flash every secound where as a 100% duty cycle at 1hz would stay on for one second, and then off for one. How does one set the duty cycle with a 555? do you have to use a dual 555 setup like a 556?

No one has commented on optics. What do you suggest as being the most bright hotspot without being too small to aim at someone's face?