The International Cessna^® 170 Association

DaveF wrote: Another lamp life-extending idea I've seen is to put a 0.1 ohm resistor in series with the landing light. It will drop about 0.75V, greatly extending lamp life, at the cost of an almost imperceptible loss of brightness. Be sure to use a properly heatsinked power resistor!

Do you think that these Lightsavers are just resistors? The description sounds more like a capacitor. Has anyone tried them? Does their explanation of its benefit sound reasonable?

An even simpler answer would be to substitute a GE 4595 lamp (13v, 100watt, 300-hour life) for the usual GE 4509 (13v, 100 watt, 25-hr life). The difference is (as mentioned in support of installing the resistors) a small loss of brilliance. This is a suggestion made by the Cessna Pilots Assoc. in their article published in '88 and revised in '98.

I am totally convinced that the life of landing and taxi lights is directionally proportional to their energized time. I've had the same lights installed for years,but I never turn them on unless I need them to see what I'm doing. I almost never fly at night. It's kind of like IFR, I don't have to do it any more.

Gary,

Looks to me like those are just resistors. Like these.

The picture on the Spruce web site is exactly what my friend's installation looked like. The Spruce description makes sense, though its intent is to sell the product, not to describe what the product actually does, which is to limit the inrush by setting a minimum circuit resistance.

From what I've seen the extra resistance does increase lamp life, but I don't know whether it's because of the lower inrush or because, by adding series resistance, you've reduced the power dissipation in the filament itself. Some of both, probably.

But as George points out, you can acheive the same thing with less work by installing a different lamp. Thicker filament, less light, longer life.

I believe that more than total energized time, the number of times an incandescent light is turned on and off affects its life (IIRC, one of Edison's original bulbs is still burning, but it rarely if ever gets turned off.) If you've ever seen a slow motion film of a light bulb being energized, you might agree. The resistance of the filament is extremely low when cold, so there's quite an inrush of current when they're first turned on, causing thermal and physical shock to the filament each time it happens. In the early days of computers before LED's, small incandescent bulbs were used on the front panel indicators. These bulbs were turned on and off many times per second, and to increase service life, a "keep warm" current was kept on the bulbs to lessen the shock when they were illuminated. It might be an interesting experiment to rig up something and test whether that same technique might work on our particular bulbs (off the airplane of course ).

Miles

On some of the Cessna 172 airplanes that had the landing lights in the nose cowling, we moved them out in the wings to improve their service life. Very effective. Apparently engine vibration was the culprit.