textfiles/survival/litebulb.txt

OF BULBS AND BATTERIES

BY JERRY REIMER

A crash awakens you from sleep, you reach for the bedside
flashlight, snap the switch on, and command a brilliant beam
adequate to illuminate and identify any potential adversary.
Blinded by the light, the intruder freezes in his tracks--the
cat, again.  Third time this week.  Off goes the beam, and the
flashlight is returned to the recharger stand to await its next
nocturnal call to duty.  And you return to bed, trying to sleep,
dreaming of feline homicide.

Or...

It's the third day on the trail.  After fourteen miles, camp is
chosen, meals prepared, and then consumed as night falls.  Weary
hikers, heavy forest, and a new moon.  No campfire lounging
tonight, only sleep.  The familiar pain of a too full bladder
awakens you.

You grab the lightweight flashlight as you exit the tent and use
it to guide your journey deeper into the woods.  On the return
trip, you note the beam's diminished brilliance.  Only a pale
yellow glow remains when you reach the tent.

How can the new batteries be dead after only three nights? you
wonder as you doze off again.

Clearly, the demands placed on the two flashlights are
significantly different.  Yet seldom are the demands of the
flashlight considered when a failed bulb is replaced.  Or perhaps
the bulb has been replaced with a new krypton bulb (that "rivals
the sun," they claim).

What are some of the technical specifications surrounding
flashlight bulbs and how do bulbs affect battery life?

Not all bulbs are created equal.

Flashlight bulbs are described by their mounting base style;
usually threaded or flanged.  They are rated by the voltage (V)
needed to operate them and by how much current (milliAmperes)
they use while operating.

Listed below are the specifications of the more common flashlight
bulbs.

Threaded    Voltage   Current
--------    -------   -------
222         2.25      250 mA
243         2.33      270 mA
 14         2.47      300 mA
 40         6.30      150 mA
 46         6.30      250 mA


Flanged     Voltage    Current
-------     -------    -------
PR4         2.33       270 mA
PR2         2.38       500 mA
PR6         2.47       300 mA
PR3         3.57       500 mA
PR12        5.95       500 mA
PR13        4.75       500 mA
PR15        4.75       500 mA

Krypton     Voltage    Current
-------     -------    -------
K-1         2.40       600 mA
K-2         2.40       830 mA
K-3         3.60       800 mA

Flashlight batteries are constructed in specific sizes-- the
familiar AA, C, and D--and are available in either single use or
rechargeable (ni-cad) types.  The single-use cells, of carbon-
zinc, alkaline, or whatever, all deliver 1.5 volts each.  Stack
two together to get 3 volts, three deliver 4.5 volts, etc.

Ni-cad batteries provide around 1.2 volts each.  Two together
make 2.4 volts, three, 3.6 volts, etc.  Obviously, the bulb
voltage needs must be met by the batteries.

All batteries are rated according to their capacity:  how much
energy they store.  Large batteries are rated for the number of
hours they can deliver 1 ampere (ampere hours).  Smaller
batteries are rated in milliampere (1/1000 ampere) hours (mAH).

Obtaining the mAH ratings from the various manufacturers is
difficult, despite their universal claims of outlasting all the
others!  The mAH ratings for ni-cad batteries are more widely
published, and typical ratings are as follows:

Battery      Volts    Current
-------      -----    --------
AA           1.2 V    500 mAH
C            1.2 V    1200 mAH
D            1.2 V    4000 mAH


By dividing the mAH rating by the current used by a bulb, an
estimate of battery life can be made.  (For example:  1200 mAH C
battery divided by 300 mA bulb equals 4 hours of battery life.)

When all these ratings are considered, the importance of
selecting the proper bulb can be realized.  Generally, for a
given voltage, the bulb with the highest current will produce the
greatest light, but for the least amount of time.

Thus, any bulb that uses twice the current of another bulb will
only operate for half as long on the same batteries.  (For
example:  two AA ni-cads have 1.2 V x 2 for a total of 2.4 volts
at 500 mAH; paired with a PR4 bulb rated at 2.33 V and 270 mA, we
have 500 mAH divided by 270 mA for a time of 1 hour, 51 minutes.
Of course, using long-life alkaline cells will provide light
longer than the ni-cad example indicates.)

Installing a high current bulb in a rechargeable flashlight
that's used around the home is probably a good choice, based on
the need for bright light for relatively short periods of time.
In the field situation described at the beginning of this
article, a little light goes a long way and inadvertently using
the wrong bulb can result in no light surprisingly quickly.

As with all equipment, choose what you purchase based on
knowledge and individual needs--even when it's as "insignificant"
as a flashlight bulb.
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