Here's a question that I have had in mind for a while, as I am returning to some structure building and lighting soon:
I have used 1K and 470 ohm resistors both with my 3mm LEDs for lighting cabooses and engines, particularly when I repower/rehab engines. I see very little difference in the amount of light that the resulting circuit produces.
In a structure interior- for both general lighting and localized lighting (such as an open loading dock interior where a view block is used to contain the effect- and where the bright light of a locomotive headlight is not desired necessarily)- is there a better choice of a higher resistor value or a variable circuit control (like a pot or rheostat control knob) that would tone down the LED brightness to make the illumination more "subtle"? If so, what solutions would be best?
I want to re-visit some of my already built structures and improve them by adding lighting, as well as one new project I am starting this spring.
Cedarwoodron
Your best bet is to bench experiment with higher resistor values until you find ones you like for each situation. The worst thing that can happen with higher value resistors is that you use one so high that not enough current flows to light the LED. That's it. Nothing can get damaged. That "dim bulb over the outside door" look might take twice the resistor value as the "light fixture in the room's ceiling". You can maybe find the spec sheets for the LEDs you are using which will show the light output vs current, which might give a hint - you cna use the current to calculate the resistor needed. The difference between 1K and 470 ohms isn;t all that much. Going from 1K to 2.2K or even 4.7K is a huge jump.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Keep in mind that resistor values depend on supply voltage. I have two basic systems. One is for the vast majority of my structure lighting and it's set just shy of 3 volts. So it starts out as toned down. I use values all the way from 1 ohm to about 100 ohms. Results like this...
I use 12 volt power in a few cases. The 3 volt requires you don't put any LEDs in series, but sometimes that's desireable. I also have a need for 12 volts in a couple of cases, like when I using a module to drive the "fire" in my smelter. Liekwise, it works well for mobile apps like car lighting. Resistance used with these ranges from 470 to over 100,000 ohms to get a nice dim effect. Here's a pic of the smelter complex. All the light from inside the buildings is 12 volt, while the outdoor light is 3 volt.
Randy's suggestion to experiment is a good one. You can get a LED to do almost anything in appreance with the right amount of resistance. So long as you have the needed minimum, you're safe.
Mike Lehman
Urbana, IL
Then, after I wrote the original post, I remembered looking into those micro-LEDs that come preconnected and are sold in rolls- do they already have a built-in resistor? Are they more suitable for structure lighting? Anyone with some experience installing these types of LEDs, please remark.
Yes, they work well in passenger car lighting, where I've used them extensively. They like to see 12 volts and can be crazy bright, which is why I use resistances of up to 100,000 ohms or more with them. I've not really used them for structure lighting yet, but have a project right now to light up some signage I may use them for.
The Radio Shack stuff is #276-0329 (for white). It has a pretty neat property you can see when you have lots of resistance in the circuit. It turns out that the 3 LEDs on the strip are actually composed of three smaller LEDs underneath a diffuser. Each LED then looks remarkably like a home overhead light fixture with three bulbs.
I haven't dissected one of the 3-LED units to see if I can use one by itself off the strip. Looks like it would work. Then you could get 3 overhead lights out of each strip unit.
if your lites and resistors are already installed you could just use a variable dc power supply, this works very well.
i`ll try uploading a little video tonite demonstrating...
trying to upload video
Am i ever gonna be able to lay any track???
True, you could. That would increase the chance of instantly toasting any of your LEDs that aren't set-up right for 12 volts if the knob got bumped. Zzzziiit. They're gone!
It's much better to use a power supply that can be adjusted to a voltage and then be difficult to unintentionally move. I make my power supplies from old wall warts and the circuit design at spookshow's website: http://www.spookshow.net/lowvcircuit.html
It is adjustable, but it's a small screw that is concealed once it's in the case. If you need more than about 7 volts, you'll have to adjust the value of the trim resistor, but this is also what I use for the 12 volt supply.
cedarwoodron- is there a better choice of a higher resistor value or a variable circuit control (like a pot or rheostat control knob) that would tone down the LED brightness to make the illumination more "subtle"?
Perhaps you're looking for a yellow/orange LED. Unlike incandecent, the wavelength of an LED doesn't change with intensity.
greg - Philadelphia & Reading / Reading
Using a lower voltage power supply is handy, but makes it a bit ahrder to vary the resistors - unless you go to precision resistors, there are only certain values actually made. With a higher voltage power supply you use larger value resistors which means there is plenty of variety even with standard 10% tolerance resistors.
Another advantage - 12V very high current power supplies are insanely cheap. You can buy brand new ones for not much money. Thing is, they have these funny molex connectors on them for computer motherboards and accessories... This works out to be an advantage since mating conenctors are also quite common, and you do not want to feed 12V at 40 or 60 amps into one bus around your layout. So you make a small panel with multiple fuses or resettable breakers at some reasonable amp value and run multiple fixed voltage buses around the layotu from one central power supply for all your lighting and accessory needs. Beats having power strips full of wall warts and so forth. I'm considering instead of actually using a slightly higher voltage (maybe 15V) AC as my main accessory bus, if I need DC I can tap off with an inexepensive bridge rectifier and filter cap, if I need a specific voltage just add a simpel LM78xx series voltage regulator. There's enough wires with the DCC track bus, having fewer by using one standard accessory voltage bus keeps the wiring down.
Those LED strips are indeed generally quite bright, since they are meant for full-scale illumination. But nothign says you can;t add more resistence and cut them down. I do like how those Radio Shack ones look, that really could be a light fixture with 3 bulbs in it, and at that brightness level it probably looks really good in a house. Since you're adding extra resistence anyway, you can always cut them apart at other than the indicated locations, just rememebr that typically they break apart in 3's ebcause they are 3 LEDs wired in series, and plan the resistence accordingly. Not sure I will go to all that much trouble but by breakign them up and putting multipel lighting circuits in each structure, you could control things so that at dusk, only certain lights go on, downstairs ina house, and as the evening progresses the lights downstairs go off and the bedroom lights come on. Neat animation tricks like that.
I would suggest building the structure and then testing different resistors until you find the one that works best. If you are going to be doing this alot, you could glue the resistors on to something like a Popsicle stick, and connect the resistors to your power supply, so all you have to do is connect the wires from the LED to your "test rig", you can even add alligator clips so it is faster and easier to use.
rrinkerUsing a lower voltage power supply is handy, but makes it a bit ahrder to vary the resistors - unless you go to precision resistors, there are only certain values actually made. With a higher voltage power supply you use larger value resistors which means there is plenty of variety even with standard 10% tolerance resistors.
Randy,
What I do is buy the 1/4 watt resistor assortment at RS. There are a bunch from 1 to 100 ohms that work well for the 3 volt circuits, a bunch above 1000 ohms that work well with the 12 LED strip lighting in my cars and a bunch in between that are all around useful. Even if there are 10% variance, it's not enough to count on that for differentiation at these low voltages.
greg,
Re wanting to get a nice mellow color in the lighting, I search out the Warm White Xmas lighting. A little harder to find, they'll work better as lighting than orange yellow LEDs (which may work well if you want the look of a modern sodium halide lamp, though.) I generally only use the Cool White LEDs when I want to simulate flourescent lighting.
Here's an example of the variation possible by throwing all these at a scene.