I haven't lit any structures with interior lighting. I have one that I would like to convert from a grain bulb to an LED, but I am sure the light will be too intense. Is it possible to simply add more resistors or a larger resistor to bring the intensity down to something resembling interior light bulb in a building? If so, do I simply wire the resistors in a series or what value would be a good single resistor to use. I guess I could experiment, I thought I would ask first. Thanks for any tips.
Yes, adding resistance will dim the LED somewhat. How much added resistance? Not all LED's are created equal so some experimentation will probably be required. I made a very simple tester for this purpose. A piece of plywood 3" or 4" into which I drilled nine holes--one in the center, the other eight in a circle currounding the center. Into each hole I put a 1" piece of 14g solid wire. I then soldered one lead of eight gradually larger resistors to each of the perimeter 14g wires and all eight of the other leads to the center post. Using three small jumper wires, make a circuit with a power supply (9v to 12v works well but it could be a bit more or less), the LED to be tested and the resistor board--one jumper from the power source to the LED, one from the LED to the center post of the resistor board and one from one of the outer wires on the resistor board back to the power supply. If the LED is too dim, move the latter jumber to a lower value resistor on the resistor board. If too bright, move to a higher value resistor.
And, yes, the resistors get wired in series. And they can be added together but always wired in series. That is, if @K resistance is needed but you only have 1K resistors, solder two of the 1K's together end to end and then put them into the circuit.
I started with 5mm warm white LEDs stripped from Christmas light string. Add a resistor 1-2 k resistor to run on 12v DC. Seems ok for small bldgs like a shack. For larger buildings, I like the 3-LED chunks you cut off in multiples of 3. Each set of 3 has resistors built in. I run all using 12v regulated walwart typepower supplies, each handles up to 1000 milliamps. I recall the 5mm leds draw 9 ma while the strip of 3 takes 25-30.
I'm not sure how much increasing resistor value can reduce light output before led voltage is reducedto the point it shuts off.
Paul
Modeling HO with a transition era UP bent
davidmbedardDiffuse it.
I second that motion.
While dimming most common LEDs can be successful to a point, if you are working inside a building you have the option of using various "filters" to change the color or reduce the intensity of the light.
Since LEDs are cool temperature-wise you can use plastic diffusers of many types.
I frequently place the amber colored kapton tape directly over the LED or I will "color" the envelope with a Sharpie® pen. Usually orange, yellow or red colors will warm up the typical cool-blue colors of many LEDs.
Look for package wrapping, translucent file folders, old slide film, Scotch tape, even waxed paper will not only reduce the light but, as David suggests, spreads the light over a broader area inside your building.
These are the LED strips I have been using lately. See the scissors "icon, where you can snip the strip apart and have a handy three LED group.
Here is a view of an "experimental" installation:
These LED strips are great since you can cut them in any group of three and get just about any length you want. The resistors are already in place for a 12V DC supply and there's even peel-n-stick adhesive on them.
I use the orange Sharpie® pen and "paint" directly on the SMD to warm them slightly. Still, you could experiment with diffusers of shades of gray to tone down the light.
Good Luck, Ed
Thanks to you all, fellows.
Well, I must be on the right track after all these years because I have some of everything mentioned. I have lots of resistors, many LEDs stripped out of camping lights, a couple of "pots", many power sources, a multimeter, and lots of kapton tape. Like my brain I have used them all only up to a point.
I think I will first try just the tape and maybe a full 1K resistor over the 750.
I think the idea of a testing board, Sagit... is very clever, especially testing those scrounged LEDs.
My "Night Scene" thread provides lots of examples and details on how to achieve various effects with LEDs: http://cs.trains.com/mrr/f/88/t/213765.aspx?page=1
http://cs.trains.com/mrr/f/88/t/213765.aspx?page=1
Putting LEDs in series can be useful, but can also get complicated. My recommendation is to use parallel circuits at first and get the basics down. Then give a LED series circuit a try. The problem is that unless you're comfortable with making the calculations, adding the different LEDs together in series can be rather hit or miss in terms of results -- and may not even light at all, which can be disappointing after a lot of work, as well as a reminder to test things as you go.
Speaking of testing, a handy go/no go tester for salvaged LEDs can be made from a simple 2-cell battery holder. Mine started as a 2 AA battery holder from Radio Shack. I added a 1k resistor to the positive lead. Simply touch the leads to the correct leads on the LED and it will light if good.
Mike Lehman
Urbana, IL
I have used inverted cone LED's a couple of times. Those emit light 360 degrees. Varied the brightness with a trimmer pot. Also, very good for a simulating a rotating lighthouse light.
Rich
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.
The very minimum with a 12V DC source is 600 Ohms. This will give you roughly 20 ma which is at the top range of most LEDs. Not all LEDs are this high a current. So read the SPECS! For example, these white LEDs use 20ma forward current:
http://www.mouser.com/Search/ProductDetail.aspx?R=VAOL-3MWY4virtualkey59300000virtualkey593-VAOL-3MWY4Most people like to use 800->1.2kOhm resistors. Each time you double the resistance, you cut the current in half (and roughly the brightness)
So 600, 1200, 2400, 4800 Ohms will give you full, 1/2, 1/4, 1/8 total brightness (more or less)
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
I have used 3mm LED's that are rated for 2ma for battery operated equipment.
Cisco Kid
You may already be aware of this so disregard it if you are.
'White' LEDs come in a variety of colours ranging from 'bright' white to 'warm' white. Your camp light LEDs are probably in the bright white category and they likely have a blueish tone to them. They are great if you are simulating florescent lighting but they don't model incandescent lighting very well. As DavidB suggested you can diffuse them and change the colour by simply painting them with a light coat of beige paint.
Or, you can buy LEDs for peanuts on eBay. My last purchase of 500 - 3mm warm white LEDs worked out to less than 3 cents each. The only caution is that you should be able to see the colour value of the LEDs in the listing. For warm white you are looking for something in the 3000 range. The higher the number the brighter the white. If the seller is simply saying "warm white" you are taking your chances.
SMD LEDs are also quite cheap (Surface Mount Device). They are great for individual lights where the 3mm LEDs are too big. They can be a bit fussy to work with if you are attaching your own leads, but you can also buy them pre-wired.
The other option, as Mike Ed mentioned, is LED strip lighting. The resistors are built in (you can always add more to dim the lights) and they are a much quicker way to achieve nicely distributed even interior lighting.
Good luck with your LEDs!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
hon30critterThe other option, as Mike mentioned, is LED strip lighting.
Dave,
It was Ed who mentioned the 12V strip lighting here. I do cover it extensively in my Night Scene thread, which may be what you're recalling.
Mike
I use Evans Designs LEDs that come with resistors & diodes already attached, so they can use pretty much any AC or DC power source. I use an old DC power pack for building and streetlight lighting. The LEDs can be dimmed just like regular bulbs, although they're maybe not quite as bright as regular 12v bulbs I've used.
In a few cases (like an isolated building near the tracks) I have hooked up the Evans LED's directly to DCC track power. It's really not super bright, I've used one in a very small building and it seems OK.