Conventional Flashlight runtime and brightness

[Airmon]

Hi all,
I was surfing around at "how much is inside"
http://www.cockeyed.com/inside/batteries/batteries.html
and ( for odd reasons ) they do a runtime test of a two D cell chinese flashlight, once each with Duracells and el cheapos.
They run them down to no-longer-glowing dead, rather than to 50% brightness, but still get 33 hours out of the cheap batteries and an astounding 116 hours out of the Duracells, claiming that it was pretty evenly bright most of that time for the latter test.

This got me wondering... the only runtimes I've seen for "conventional" flashlights are for minimags and micras.
Anyone interested, for comparison's sake, in running a rumtime test ( or posting some, if you already have them ) on some conventional "classics" like 2,3,4 cell C and D cell Maglights, yellow and black "industrial" flashlight?

I did a search for maglight and runtime here on CPF, coming up with
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Number=390190&page=&view=&sb=5&o=&fpart=all&vc=1
showing a 4-D maglight runtime to 50% of just under 2 hours, which wouldn't seem to jive with the kind of results in the "how much is inside" example.
Thoughts?

/ubbthreads/images/graemlins/confused.gif
Airmon

 

[evan9162]

The light on the "how much inside" test was likely like the cheapo, old version of the everady 2D light. These have a PR2 bulb which starts out dim and sickly yellow, and doesn't draw much power, whereas the mag 4d has a krypton bulb which is likely driven harder, so the batteries are drained faster.

 

[Airmon]

So- What's the current draw of a pr2 bulb, and the krypton bulb in the Mag?

 

[evan9162]

Well, from what I can dig up, the PR2 draws 0.5A, whereas a Krypton bulb may draw more (0.7A?). The other thing to note is that they claim it maintained pretty even brightness. That's a very hard thing to quantify by just using your eyes, as they adjust to brightness levels so things appear even, whereas the mag runtime test you linked to used an actual light meter, so no guessing was involved.

The other thing to note is that there may be high resistance in the cheap light's contacts, reducing bulb voltage and reducing power use to the bulb.

 

[Airmon]

That's not a lot of difference in current draw.
So nobody has any "baseline flashlight runtime" values for these?
Sounds like a gap in our knowledge...

 

[evan9162]

The current draw is probably not the main factor. The main factor is likely using the human eye to say "output looks the same" vs. using a light meter to establish the 50% mark.

The other thing to note is that incandescents on alkalines typically drop brightness very quickly. Look at the AA minimag plot made by Roy (one of the sticky threads in this forum). The output drops from an initial value of 35 (which drops from the peak very rapidly) down to 17 in about 2 hours. However, after that, the output is relatively flat until 7 hours. Also note that after turning off the light for a while (and giving the batteries a chance to "rest", or recover some voltage), and turning on the light again, it's again about as bright as it was at the 2 hour mark.

I would expect D cells to exhibit the same behavior, although the leg after the 50% mark would extend out many hours longer

 

[Mathieas]

Thanks for the info.

 

[SilverFox]

Hello Airmon,

In my battery testing, I ran the D cells down to 0.5 volts. At the 0.5 Amp Rate that took close to 25 hours.

A 3 volt lamp running at 1 volt will still glow, but I am not sure how useful that glow is.

The D cells start at a little over 1.5 volts. I checked the voltage at 2 hours and it was a little over 1.3 volts.

I find extended run times interesting, but I don't think a dim glow will light up things that go bump in the night. I'll stick to the 50% value for that.

Tom

 

[Lynx_Arc]

Two D cell chinese flashlight means who knows what bulb they put in it. It could be a pr2 .5A 2.4v or a 2.4v .2A or less. They have all sorts of odd PR based bulbs out there I have some PR17s I think .33A 4.9v, these would last longer than regular 6v type bulbs by about 1/3.