Light bulbs

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Let'sgoflying!

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Dave Taylor
I have a couple of small interior light bulbs in the airplane (map lights) which I have always disliked because they make too much heat imo. They are the correct size bulb.
GE67 and GE89
I would love to change them to a newer style ie LED if available.
One problem is that the lamp fixture takes light off the side of the semi-spherical bulb. So a replacement bulb would have to be similar in configuration I think.
Possible?
Alternatives?
 
Careful with LED replacements. If you put them in backwards, they won't work. I learned that the hard way when I put some in license plate lights in my truck. Flip them around instead of getting annoyed they don't work.
 
LED bulbs can be dimmed, but not by use of a rheostat; rather, you must use a PWM (Pulse Width Modulation) dimmer.
 
A little sidetrack but I have a quick story about light bulbs. Many, many years ago when working for an airline, we had a warning light (I forget which one) that was illuminated and wouldn't extinguish. When we didn't get it fixed right away, the supervisor suggested replacing the bulb. Yeah, replace a bulb because it's lit. :confused: Ended up being a logic card.
 
weirdjim said:
I don't believe that is true. They are dimmable by reducing the current through them, just like an incandescent.

Jim
Click to expand...
LEDs tend to flicker when dimmed using a traditional dimmer.

I'm not an electrical engineer. Just speaking from personal first hand experience.
 
weirdjim said:
I don't believe that is true. They are dimmable by reducing the current through them, just like an incandescent.

Jim
Click to expand...

No way, no how, I am challenging your knowledge!

I have been told by folks who seemed competent to comment that reducing voltage (to reduce current) would dim LEDs to a point, after which they'd simply extinguish.

But I also admit to never having looked at how LEDs behave in DC dimmer circuits directly.

And, upon further reflection, I am recalling that the comments I reference above were in the context of home lighting, so we were talking about dimming AC circuits and their input into LED lamps which had to have rectification and other bits of magic and ledgerdemain going on, so... now I have to go and pop an LED lamp into a post light and dim it for experimentation purposes.
 
I am NOT an electrical engineer.
So below is based on what I learned dealing with LED lights in home, many of the lights I have are dimmable.
Dimmable LED lights come in two basic types. Voltage based and Wattage based. Wattage based generally have a large rectifier in the base of the bulb and use traditional rheostats to control the light level; and a are popular option for retrofits on existing fixtures. New LED fixtures which are designed for LED and not a retrofit, use a voltage regulator at the dimmer.

So the answer is, it depends.

Tim
 
The brightness to voltage curve for a nekkid LED is pretty steep - not much change in voltage gets you from dark to burnt out.

diode12.gif

You can play with a series resistance to change brightness, but I suspect that the range of resistance to dim an incandescent bulb wouldn't be a good match for an LED even if the LED is simply connected with a series resistor for current limiting. The referenced replacement way up above says it's good for 10 to 24 volts which would suggest it uses something more sophisticated than just a series resistor for current limiting and that it is not likely to dim properly with just a rheostat, but I wouldn't know what is inside it.

For house stuff - the method used to drop the voltage from 110 AC to a few volts DC would affect how the lamp reacts to a dimmer and this may not be very relevant to how a 12V replacement bulb would work in an airplane.

For the fun of it - LED vs. series resistance vs. voltage:


 
I heard that there may be LED dimming issues. I went online, ordered LED replacement bulbs for a few of the panel bulbs to test it out. Plugged in the new ones and they dim with the normal Cessna rheostat.
 
ircphoenix said:
LEDs tend to flicker when dimmed using a traditional dimmer.

I'm not an electrical engineer. Just speaking from personal first hand experience.
Click to expand...
I am. You are talking about AC bulbs that use pulse width modulation with zero crossing DIACs to do the detection. I'm talking LED bulbs in a DC application with linear dimming.

JIm
 
tspear said:
I am NOT an electrical engineer.
So below is based on what I learned dealing with LED lights in home, many of the lights I have are dimmable.
Dimmable LED lights come in two basic types. Voltage based and Wattage based. Wattage based generally have a large rectifier in the base of the bulb and use traditional rheostats to control the light level; and a are popular option for retrofits on existing fixtures. New LED fixtures which are designed for LED and not a retrofit, use a voltage regulator at the dimmer.

So the answer is, it depends.

Tim
Click to expand...
Radar Contact said:
I heard that there may be LED dimming issues. I went online, ordered LED replacement bulbs for a few of the panel bulbs to test it out. Plugged in the new ones and they dim with the normal Cessna rheostat.
Click to expand...

Q.E.D. Thank you for proving the point. Sometimes the level of misinformation in this group rises to the incomprehensible level.

Jim
 
Capt. Geoffrey Thorpe said:
The brightness to voltage curve for a nekkid LED is pretty steep - not much change in voltage gets you from dark to burnt out.

You can play with a series resistance to change brightness, but I suspect that the range of resistance to dim an incandescent bulb wouldn't be a good match for an LED even if the LED is simply connected with a series resistor for current limiting. The referenced replacement way up above says it's good for 10 to 24 volts which would suggest it uses something more sophisticated than just a series resistor for current limiting and that it is not likely to dim properly with just a rheostat, but I wouldn't know what is inside it.
Click to expand...

You don't "play" with series resistance, it becomes part of the circuit of the LED. And you don't use them "nekkid". You use a series resistor inside of the bulb housing itself to limit the current.

But I'm wasting words. Some feller tried it (see above). It works just like I said. Argument over.

Jim
 
weirdjim said:
You don't "play" with series resistance, it becomes part of the circuit of the LED. And you don't use them "nekkid". You use a series resistor inside of the bulb housing itself to limit the current.

But I'm wasting words. Some feller tried it (see above). It works just like I said. Argument over.

Jim
Click to expand...
Thems fightin' werds on POA. o_O;):)


(It's a joke, I say a joke)
 
Jim, I don't think there ever was an argument! Your knowledge is a pretty known thing.
 
weirdjim said:
I don't believe that is true. They are dimmable by reducing the current through them, just like an incandescent.

Jim
Click to expand...

When you make a blanket statement like that, those of us who aren't in the know only know that you're wrong when stating this. So the enlightening post about DC vs AC was a reasonable correction.

Bitching that we didn't know what you were talking about after you made a universal statement isn't entirely reasonable.
 
weirdjim said:
Yeah, I know. "My mind is made up, don't confuse me with facts!!"

I'd like to have a couple of these folks in my classroom for an hour, just an hour, I tellya. :cheers:

Jim
Click to expand...
Come on Jim, I = V/R is complicated.....

Bob
 
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