I just replaced the incandescent bulb back up lights with Miniatronics 3mm Yeloglo White LEDs on my Proto Heritage 2-8-4 steamers.
These LEDs are listed a Ultra Bright and, indeed, they are bright, not only ultra bright but also extremely ultra bright.
The LEDs come with two choices of resistor, a 270 ohm and a 470 ohm. Way too bright for a tender back up light IMHO.
I wound up installing 1.5K resistors, and they are still blindingly ultra bright. I sure would have thought that a 1.5K ohm resistor would sufficiently dim the LED but not so.
I left the 1.5K resistor on the LED, but I wound up testing all the way up to a 5.6K resistor to sufficiently dim the LED to my liking.
Any thoughts or comments?
Rich
Alton Junction
Not unusual, I belong to a number of train forums and have seen as high as about 3.6 k. I doubt many model train employees work for these companies. Engineers no doubt just consider the LED’s max specs, usually around 20 to 25 ma.
I keep a 2.5 k pot for 20 ma LED's. I would check and use a close standard value out of the junk box. Never have to use math. I found out years ago, this is model railroading. Not rocket science.
Some might keep a 10 k pot for super bright LED's.
The resistors would be quite normal for standard brightness, though I never had to go below 870 or so for standard LED.
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Neither resisotr that comes with it is correct for DCC. I always use a 1K resisotr, but none of the locos I have has the LED directly visible - it's walays through some sort of plastic light pipe, which kills a lot of the brightness (unlike a fine glass optical fiber or lens which wouldn;t attentuate much light). Perhaps the sole exception so far is a Staewart/Bowser AS16, which has a shorter plastic lens compared to say P2K locos which also appears MUCH clearer (optically) than P2K's light bars. In fact, looking into it from outside the loco seems to greatly magnify the LED. I added one of the 470 ohm resistors in series with a 1K in that one, effectively approximately 1.5K. With the room lights dimmed it actually throws a visible beam of light down the tracks.
Like most white LEDs, the YeloGlo has a 20ma maximum current limit. A 1K resistor at typical DCC voltages results in about 9ma through the LED - less than half the limit. High efficiency LEDs can work on much less though. I did a little messing around on a breadboard with a basic red led, and not (as far as I know) specifically a high efficiency type, just some random ones that cam in an Arduino kit. At 5 volts it was visibly glowing with a 100K resistor. Most red LEDs are around 3.1 volts, so if you calculate that out, it was .029ma. I had to turn the lights off on my bench to see it but there was a definite difference between power on and power off. Utterly useless for any practical application, but it was plenty bright to see it was lit up with less resistance with a current of around .1ma. A more scientific test of this was done by Dave Jones at EEVBlog, he got his hands on a sensitive photon detector and tried an experiment of reducing the current to an LED to see where the minimum was that the detector could see it actually emitting light. It was at a remarkably low current, but also too faint for the human eye to detect. So yes, LEDs can be more than bright enough with well over the commonly used 1K resistor value. Most people using surface mount LEDs use much more than 1K as well - typically a SMD LED is either directly visible or behind a very thin lens, so there is nothing to attenuate the light, and they also tend to be high efficiency types. It's not uncommon in a very low power circuit that a single LED indicator, even with less than 1ma going through it, is one of if not the highest single consumer of current in the whole device.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
You did exactly as I have done, although I don't recall ever needing quite that much resistance.
Another idea would be to paint the LED with some clear glass paint like stained glass paints. I'm not sure this would work but it might be worth a try. Maybe a light gray to tone things down? Or a cream color. I think I would stay away from yellow or orange but that is a matter of personal taste.
From my own observations and the replies to this thread, I am concluding that higher resistance levels do not necessarily dim the Miniatronics Ultra Bright LED sufficiently.
It surprises me that even a 1.5K resistor does not sufficiently dim the Miniatronics Ultra Bright LED. Furthermore, it surprises me that there is little difference to the eye between the effect of a 470 ohm resistor and a 1.5K resistor on this LED.
I am going to look into coloring the LED or the plastic lens on the rear of the tender as a method to dim the light effect.
Thanks for all of the replies.
richhotrainI am going to look into coloring the LED or the plastic lens on the rear of the tender as a method to dim the light effect.
Hi Rich:
I have painted LEDs to adjust the colour tone but if you are happy with the 'colour' (Canadian spelling eh!) then I would simply use a higher value resistor instead of paint. I have used resistors as high as 33,000 ohms to get LEDs down to something that resembles an early incandescent lamp or a kerosene lamp. In your case I'm guessing that 6,000 - 10,000 ohms might be better for a headlight. Years ago I bought an assortment of resistors from Digi-Key (cheaper on eBay now) so I can play with what looks right to my eye. I didn't buy every available value but I have enough variety to cover most applications up to 100K. Here is the range that I use for LEDs:
680, 820, 1.0K, 2.2K, 3.3K, 4.7K, 6.8K, 10K, 33K, 100K (never used 100K yet - too dim).
I used a 33,000 ohm resistor for the LED over the conductor's desk in this caboose. The camera makes it look brighter than it actually is. If you compare it to the marker lamps you can see that the camera has over exposed the markers:
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
hon30critter richhotrain I am going to look into coloring the LED or the plastic lens on the rear of the tender as a method to dim the light effect. Hi Rich: I have painted LEDs to adjust the colour tone but if you are happy with the 'colour' (Canadian spelling eh!) then I would simply use a higher value resistor instead of paint. I have used resistors as high as 33,000 ohms to get LEDs down to something that resembles an early incandescent lamp or a kerosene lamp. In your case I'm guessing that 6,000 - 10,000 ohms might be better for a headlight. Years ago I bought an assortment of resistors from Digi-Key (cheaper on eBay now) so I can play with what looks right to my eye. I didn't buy every available value but I have enough variety to cover most applications up to 100K. Here is the range that I use for LEDs: 680, 820, 1.0K, 2.2K, 3.3K, 4.7K, 6.8K, 10K, 33K, 100K (never used 100K yet - too dim). I used a 33,000 ohm resistor for the LED over the conductor's desk in this caboose. The camera makes it look brighter than it actually is. If you compare it to the marker lamps you can see that the camera has over exposed the markers: Dave
richhotrain I am going to look into coloring the LED or the plastic lens on the rear of the tender as a method to dim the light effect.
Yes, the effect of reducing current to the LED is anything but linear. So the difference between 18ma and 9 ma (470 ohm vs 1K, at 12V) is not very noticiable (it's measureable by instruments, but much the same to the human eye as you found out). The curve gradually steepens, and at the low end when the LED barely lights it can be a difference of nanoamps between LED being visible and LED being too dark to see. That's why for 'dimming' LEDs, PWM is almost always used.Full on, full off, the greater the percentage of on time, the brighter it looks to the human eye. Controlling the current is much more touchy for any sort of precision in dimming. So go ahead and try a 10K resistor, it can't hurt anything.
LION uses 1K ohn resistors as the standard of him for all LEDs. You would have to go to 2K ohm or more to dim the lamp.
LION builded signals using recycled Christmas LEDs, Far too bright they are.
Mission is solved by the additon of visors. Subways do not have visors in the tunnels, but adding them makes the light look much better.
I used Coffee stirrers for the visors, cut them at the correct angle, reamed out the center web and inserted the LED. The mast needed a slighty larger hoe to accommodate the stirrer, but that was the easies addition of a visor that I have ever concoted. Keeps the light focused down the railroad.
In other places, install LEDs where the lamp itself is not seen.
ewe can also use a fiber optic from the led to the place where you want the light to appear. Make the interface tight with some shrink tubing.
Gotta try that for making street lamps, thanks for the great idea, LION.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS