Hi, I managed to run across several (bought one) Energizer 2-tube folding fluorescent lanterns today.
It has two 4W tubes and runs on 4 D cells. You can switch on one or both tubes (can't alternate which tube runs so if you're using it a lot on one tube, it might be worthwhile every battery change or two to swap tubes).
It CLAIMS (I just got it) to run for 40 hours with one tube and 20 hours with two tubes.
One tube (at one foot) gave me about 8 cd and two tubes peaked at about 13 cd.
Since this is pretty even illumination over a broad range, I would estimate perhaps 0.7 * pi * 11 or about 24 lumens output. Not bad for alleged 20 hours burn time.
Let's do the calcs for burn time.
18AH to 0.8V (or so) and 8W at 6V is about 1.33A so I don't believe the burn time. As the voltage drops the light will, too OR the current will go up.
Perhaps they're starving the tubes?
Yup...both tubes about 0.68A or 4W for both tubes and 0.37A or 2.2W for one tube (assuming no significant voltage drop from 6V).
Those current drains do match the run times one would expect--and it's not even asking it to go to 0.8V.
Two tubes work at 0.5A and 4.5V which is a fair indication of how far you can easily go down in voltage and they were still quite bright. Two tubes were very dim but would still work at 3.0V. At 3.0V the two tubes also draw 0.5A.
I have one but have managed to loose it in the house. Great for scout camps and stuff, poor mans alternative to those Coleman propane lanterns I dare say. Wouldn't take it on say a hiking trip though, those D-Cell batteries are heavy!
Using D cells is an advantage. Flashlight batteries are priced about the same regardless of size: Ds go for about as much as AAAs. But the physically larger cells store more energy, so you get more for your money in batteries if the lantern uses Ds.
C and D cells cost considerably more than AA/AAA cells around here... perhaps twice as much for alkaline in quantity.
Personally I like the idea of CCFL flourescent and LED together because CCFL tubes last a long time, are smaller and put out the same amount of light as standard tubes. With LEDs in a lantern you can run it at a lower setting increasing runtime tremendously... possibly even allowing the use of smaller batteries/weight.
Brilliant, what I wanted to say, but was too lazy to look it up. I'm not sure why going from the tiny cells of a 9 volt to the D cell the resistance would be lowest with AA cells, but the rest of it makes perfect sense.
It could be a lot of internal resistance has to do with the electrode and the optimal size for the type of electrode technology used in alkalines in AA, with AAA and less being too small in volume or surface area along the electrode and larger cells having electrolyte too far from the electrode to take advantage of it directly needing to sort of handshake electrons too much through the electrolyte in order to pass current. This is all speculation on my part though.
I was a bit suprised too when I saw that AA had less resistance than D's, but after thinking bout what Lynx said about the area ratio, it makes sense...I *think* the ratio of the electrode area to the depth or thickness of the electolyte would drive the cell resistance.
There are probably other factors at work there too.
It the differences are mainly in their high load behaviour. D cells drop their capacity much, much more at higher loads (which has nothing to do with internal resistance), look at Silverfox' data therefore.
You do not need much load and AA cells are even more cost effective (but that, of course, depends highly on the price difference from AA to D cells).
Slightly off topic but related, this light performs very well using D nimh cells. Loooong runtime between charges, and you never think twice about using both tubes all the time.
I think I posted this elsewhere sometime back, but here it is for fans of this light: Home Depot stocks Philips replacement tubes that are a wonderful 3000 degree color, not the iritating cold medical lamp washed out blue tint. The warm incan-ish color from this light makes it MUCH nicer to work with and have on near you for extended burns. FWIW.
Get two 4 watt black light bulbs and a mirror ball and have a power outage block party during the storm season. The reason D cells work well is both tubes together draw about 600-700ma which is sort of a sweet spot so to speak. Seems manufacturers of lamp know this as when they go to dual or single tube lights of over about 9watts they go from 4 to 8 D cells in the lights. This probably drops the current down close to 500-700ma again.