LEDs vs GOW bulbs?

[Ray Dunakin]

I see a lot of folks using grain of wheat bulbs for lighting of structures and rolling stock. Isn't it difficult to replace those bulbs when they burn out, especially if it's glued into a scale lamp fixture?

Why aren't LEDs used more frequently? They almost never burn out and use much less power. I had a keychain type that was powered by three button cells. As an experiment, I left it turned on to see how long it would glow before the batteries ran down. It lasted over three weeks!

I've been thinking of replacing the headlight on my Buddy L loco with a battery powered LED. It would be a lot brighter and would produce constant lighting regardless of the speed of the loco.

[John Busby]

Hi Ray
My personal opinion on this is GOW or similar look better as building lights.
I think LED's are good for head, tail/marker and signal lights where a clear
definate light is needed LED'S don't have the light spread a GOW does.
I keep meaning to see if the superglue on the lens trick I was told about works to get a bit more spread so I can simulate oil lamps in passenger coaches with yellow ones.
I also think there is a lot of ARGH!! I don't know electronics associated with LED's inspite of its only a case of find posative and the right size of resistor and hey presto it works off the transformer without going FRITS OPPS!!
it just burned out.
I have yet to see anything that looks like a good flouro light or one of those mars light thingo's.
regards John

[kstrong]

The other part of the equation is the color of a GOW bulb vs. an LED. "White" LEDs are actually on the blue side of things, and "Yellow" LEDs are simply too yellow to look like an incandescent bulb. I favor GOWs just on that alone. You just can't capture the look of a dimly lit station platform at night with anything other than a dimly lit incandescent bulb. (That, and John's comments about the "which resistor do I use?" aspect of working with LEDs.)

Later,

K

[cabbage]

I use 'grain of rice' bulbs here in the UK. I have used the so-called 5V and 12V LEDs -the ones with the built in voltage regulators. But I have to agree with Kevin -the colour of an LED is not right -but in my case it is for acetylene gas lamps on the station buildings.

regards

ralph

[Ray Dunakin]

Hmm... I didn't know a resistor was required for LEDs. What does it do, and how can you tell what kind to use?

[kstrong]

The resistor is needed when the voltage going to the LED exceeds the voltage the LED is designed to use (typically between 1.5 and 3 volts DC). As to the value of the resistor, that's dependent on the voltage and the particular LED. Someone who's a bit more well versed in electronics theory will have to answer how to determine the correct resistor to use. It's been far too long since I designed any kind of electronic circuit. (See Ralph's next post. - Thanks!)

Later,

K

[cabbage]

To operate an LED from a given voltage a resistor needs to be connected in series with it. The correct value in Ohms can be calculated from the following formula:

R = ( Vs - Vf) / If

Where :

Vs is the supply voltage.
Vf is the forward voltage drop across the LED.
If is the forward current through the LED.

The values of Vs and If are normally found in the specs for the LED.

viz:

For a typical LED (If = 20mA and Vf = 2.5V) to operate from a 12V supply.

R = (12 - 2.5) / 0.2 = 475 Ohms

The nearest easy available one would be 470 Ohms and in practice this would work quite well.

regards

ralph

[Ray Dunakin]

So as long as the voltage doesn't exceed the limits of the LED, it won't need a resistor?

[cabbage]

Yes, if you have a couple of NiMH batteries at 1.2V each then the resultant voltage 2.4V, would light the LED in the example above -and not need any resistor.

regards

ralph