[VAC] Re: Compact Flourescent Bulbs

[Dr. Gerald N. Johnson, electrical engineer]

There are different phosphor colors available in fluorescent lamps. The
greenish "cool-white" which is most commonly available is most energy
efficient. Warm-white sacrifices a bit of energy efficiency for a more
orangish tint to the light.

The phosphors in the compact fluorescents tend to be somewhat different
from the classic fluorescent lamps. This is reflected in the Color
Rendering Index. I believe the CRI is a measure of spectral smoothness.
Classic fluorescent phosphors are characterized by a few narrow spectrum
components while the lamps with improved CRI have more components to
their visible spectrum to make that spectrum smoother.

Unfortunately more sophisticated phosphor mixtures to create improved
CRI are more expensive (maybe only because of smaller production
quantities) and are not as commonly stocked at home centers or discount
department stores like Walmart. Compact fluorescents don't use the
classic phosphors so are inherently have better CRI.

Quartz-halide incandescent lamps are a bit more efficient than regular
bulbs because they operate the quartz envelope hot enough to evaporate
tungsten off the inside and so resist the gradual darkening
characteristic of standard lamps. There is some chance that the tungsten
may happen to redeposit on the filament, but not a great chance that the
redeposit will be uniform enough to lengthen the life of the filament.
Incandescent lamp filament life is cut in half by a 5% rise in filament
voltage, accompanied by a 10% rise in light output. The best
incandescent lamp has rotten efficiency for producing light, most of the
lamp out put is heat.

New technology that is coming for low voltage include white light
emitting diodes. They tend to have narrow beams, but decent
efficiencies. The initial offerings probably have as much of a spectral
smoothness problem as the classic fluorescents because the white LEDs
are based on blue or UV LEDs coated with phosphors.

Hosfelt Electronics has a selection of these LEDs at reasonable prices
(www.hofelt.com). I've not yet experimented with them. There are LED
packages that will fit standard miniature lamp sockets. Certainly the
right sizes for use in markers and maybe RV interior lighting, if the
light angular distribution is useful. Other electronics distributors
also are beginning to carry these LEDs.

A LED flashlight can run on a couple camera or calculator sized cells.
I've not yet compared the light to that from my trusty 3 D-cell
flashlight.

Talking efficiency: No lamp should be run to extinction if the user is
concerned about lamp efficiency. All lamps gradually loose output. In
the incandescent lamp this is due to a tungsten coating on the inside of
the glass. Fluorescent lamps loose efficiency due to damage to the
phosphors and cathodes. Sometimes the phosphor is contaminated by
condensed mercury from the required mercury vapor. Mercury vapor lights
commonly used as rural yard lights and in campgrounds will sort of light
for at least a decade beyond their rated lifetime of reasonably
efficient operation. When their light is greenish, they should have been
replaced a few years before. I've been continually amazed at the
improved light level each time I've replaced those greenish lamps.

Gerald J.



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