Urgh...batteries suck

[KennyR]

@Karlos

They are white (although they look slightly bluish), and they are brighter than most ordinary flashlight bulbs. A Lightwave 4000 (with 10 white LEDs) which is advertised to run with 900+ hours on 3 D batteries, and a Lightwave 2000 (4 white LEDs), advertised for 340 hours on 3 AA. Actually they'll probably still be bright enough to read by long after that. So they ain't high current! ;-) (The LW4000 is probably the world's most efficient flashlight, and I had to ebay for it and get it stateside.) Oh, and my kinetic, with its purple LED that seems to be lit no matter how long the thing is left on. But isn't very bright.

LEDs rule, but they have one important failing: they don't throw a beam. Further than 10m, they're useless. Thats why some manufacturers are making hybrids with both xenon/halogen bulbs and LEDs. LEDs for ultimate battery economy, bulbs for long distance.

It seems even the world's most efficient flashlight still suffers from parasitic drain.

[Karlos]

@Kenny

Yeah I know that they aren't current hogs compared to conventional bulbs :-) However a superbright red LED (harder to see though) would probably give twice the battery length. A  green version would look far brighter to the human eye and still last maybe 60% longer than white LEDs.

Still, try selling a green torch :-D

[blobrana]

Hum,
i suppose that
If kennys ancestors had evolved on different planet orbiting a different coloured star then his eyes may more sensitive in other wavelengths,
But for humans i recon it's red, blue and yellow.



@Kenny
Ever considered keeping your batteries in a fridge? (In sealed bags of course)

[bloodline]

blobrana wrote:
Hum,
what is flat output?

A steady flow of electrons, er, as opposed to wave-like output?

BTW, has anyone actually made a battery here?

I built a fuel cell, a simple Hydrogen Oxygen Bacon cell. I used 8 molar Potassium Hydroxide at 60 degrees C as the electrolite and nickle as the catalyst/electrode.

My Supervisor was not happy about boiling Potassium Hydroxide... and was really not happy about 8 molar bubbling away.

I built the chasis of the fuel cell using perspex (acrilyic) and used Araldite to bond the pespex.

The potassium hydroxide disolved most things, including the araldite, the perspex and the skin on my hands.

My aim was to develop a practical Methanol Fuel cell, but I ran out of time, just trying to over come the problems with the Hydrogen Oxygen cell.

The electrolite was poisioned by water produced int he reaction which reduced the efficiency after about 15mins.

I got voltages as high as 1.1volt, but I nover got the current above 5miliamps... this was probably due to the relativly small surface area of my catalyst.

Thus ended my quest for a nobel prize :-)

[bloodline]

The Band gap required to produce Blue light is HUGE.

[Karlos]

bloodline wrote:

The potassium hydroxide disolved most things, including the araldite, the perspex and the skin on my hands.

What, boiling 8M KOH attacked the stuff? Now there's a surprise :-P

You should have used a pure petroleum wax coating inside the case, obviously choosing one with a melting point higher than your operating temperature. KOH wouldn't have eaten it...

-edit-

Assuming it was aqueous KOH and not alcoholic, of course ;-)

[T_Bone]

blobrana wrote:
Hum,
i suppose that
If kennys ancestors had evolved on different planet orbiting a different coloured star then his eyes may more sensitive in other wavelengths,
But for humans i recon it's red, blue and yellow.

Green mostly, we can detect greem better than any other wavelength, given that we're not colorblind :-)

[Karlos]

Colour blindness has nothing to do with green receptivity. It so happens the monochrome cells that make up the majority of the retina respond to light in the green/yellow region of the spectrum. Those cells aren't used to judge colour, only brightness, hence we see green as brighter than other shades regardless of wether or not we percieve the colour itself.

-edit-

Given the spectral class of our sun (G2/Yellow), this makes perfect sense - we'd be hopeless if we depended on eg far red for our overall brightness information :-)

-/edit-

Trust me, I'm extreme red-green colourblind ;-)

[KennyR]

Karlos wrote:
However a superbright red LED (harder to see though) would probably give twice the battery length. A green version would look far brighter to the human eye and still last maybe 60% longer than white LEDs.

There are green torches out there. You're quite right in that green LEDs are both more efficient and mostly useless, but wrong that they would look brighter. The human eye sees about 1/3 of reflected green light, while it sees 2/3 of white. Have a look at this Q&A on the flashlight review site.

[KennyR]

Blobrana wrote:
Ever considered keeping your batteries in a fridge? (In sealed bags of course)

I don't really have to go to those extremes: alkalines lose about 2% charge per year somewhere like a drawer. But fridge or drawer, they're not in the flashlight where I want and need them. I could go with X-ray's suggestion and fumble about with my kinetic to find them, but then I wouldn't be properly ready for armageddon. ;-)

[KennyR]

bloodline wrote:
The Band gap required to produce Blue light is HUGE.

It's no big deal. You just plug the band gap with a suitable dopant.

[Karlos]

@Kenny

I meant that green would appear brighter than red (thinking along the single wavelength LED approach) :-D

Naturally white would appear brighter still since it is the sum of all wavelegths...

[blobrana]

[color=33CC00]@Karlos
Hum,
Interesting,
Though i suspect that T bone is also correct in that it`s  a  yellow-green colour that we are most sensitive to (er, cos the yellow `band` is very narrow).
but, er, i`ve never bothered to look, in depth, into the mechanics of  the human eye.
[/color]

[bloodline]

but, er, i`ve never bothered to look, in depth, into the mechanics of the human eye.

It's more Chemistry than Mechanics...

[Karlos]

@blob

I'm sure I said yellow/green in that last post ;-)

@bloodline

Maybe she meant Quantum Mechanics, in which case she's spot on ;-)

[blobrana]

Hum,
yeah,






----------------------------
 Anyway , i noticed T bone said `greem`... :-)