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DC Lighting Information and Run Times of Electrical 
Loads Powered By Batteries:
DC LIGHTING INFO:
We are all concerned with getting the most light from the amount of power
used, especially in a solar powered system.
> Our first recommendation would be to use fluorescent lamps. They are the
most energy efficient, have the longest life and produce the least amount of
heat (except for L.E.D. lamps.) The major drawbacks are that some types
will not work in very cold climates and they all need a minimum voltage
to start. When using a light sensor (on at dusk, off at dawn) they require a
solenoid or relay to fire up. Current fluorescent light fixtures have excellent
light color characteristics. NOTE: d.c. flourescent light fixtures use the same
tubes as found in a.c. fluorescent fixtures. It is the electronics, not the voltage,
that allows these tubes to be used in a low voltage d.c. light fixture.
> Our second recommendation would be quartz halogen lamps. They are
the most energy efficient incandescent (heat into light) lamps and have the
best light color quality. The downside is that they can produce a great deal of
heat and should only be used in an open fixture.
> Our third recommendation would be LED (light emitting diode) lamps. They
do not produce a great deal of light (except for the expensive multi-LED
units) but they are the most energy efficient and their lifespans can easily run
over 50,000 hours.
In an application where total reliability or the utmost efficiency is required,
the l.e.d. lamps are truly worth the money.
We can not recommend 12 volt incandescent RV and Auto types of bulbs.
These screw in or bayonet style bulbs use a lot of power and produce very
little light. 
You will see lights commonly rated at 27K or 41K.
This refers to the color temperature of the tube or lamp in degrees
Kelvin.
The higher the number, the cooler (or closer to sunlight which has a
color temperature of 5500 degrees Kelvin at noon) the color.
Most people prefer the cooler temperature (which is why we only
stock cool tubes and lamps) as they "appear" to put out more light.
A cooler light will also have less influence on the color its
surroundings.
copyright John Drake Services, Inc.
RUN TIMES OF ELECTRICAL LOADS POWERED BY BATTERIES:
A simple and realistic way to determine the run time is to take the battery amp hour rating, deduct 20% and divide the remainder by the amp hour rating of the light or electrical load. EXAMPLE: a 100 amp hour battery running a 13 watt fluorescent lamp: 100 less 20 (20%) = 80, divide by 1.08 (the load amp hour usage) = 74 hours approximate run time. This is only a guide as the battery condition, temperature and on/off cycles can affect these times. The more often you let a battery rest, the more power you will be able to pull from it.
copyright by John Drake Services, Inc.
Tom's ballast cart: