Thanks, Ken and MRH.

You've explained and illustrated lighting details in ways I had never thought to consider.  And how you do it by selecting varying beam widths of LED's is one of those "now why didn't I think of that" great ideas.  Thank you.

Regarding the resistor multiplier formula:  it's worth mentioning that if that third stripe on the resistor is black, you multiply by "1" and not zero.  (by definition:  a number to the zero power is one).

Dept of Corr.:  is there text missing at the last paragraph of the last page?

Regarding the third strip on a resistor, it might be easier to think of that band as an indicator of how many zeros there are after the first two numbers. In your example, if the third band had been red, there would be 2 zeros, so the value would have been 4700 ohms. If it had been black, there would have been 0 zeros, making the value 47 ohms. It all works out the same. It just seems simpler me to not have to think of powers of ten.

Bob Hayes

By the way, if the third band is silver or gold, don't even waste your time with it.  The values would be less than 10 ohms, regardless of what the first 2 bands were.

Bob Hayes

Very well done and timely!  Thank you for this great method and the "how to"

Rick

Your experience with set design gives a whole other dimension to a lighting article.  I never considered lighting the way you have here.

Great information on LED choices.

Thanks for the great read!

Don

Thanks for the compliments...

re:  missing text.  Somewhere in the editing process, the words STEEL MILL were left out. 

I really want to subtly color the various components of the scene, and use some flashing lights as well to simulate the hot iron products.  This task is going to involve some electronic circuts that are under development.  More on this later!

Ken

Is it possible to wire LED's directly to use something like the dimmer offered by Super Bright LED's instead of working with the resisters?

Sgmaitland@comcast.net

The resistors are used to limit the current going to the LED's to avoid "burning" them out.  The dimmers in question may also do this but they are ultimately intended for use as an LED dimmer using pulse width modulation rather than  constant DC power being applied to the LED.

Edit: Here is some information quoted directly from the Superbright LED site.

Please note that the following information applies only to single LED components, not LED Bulbs and Products
All of our LED bulbs and products have resistors built-in for operation at their rated voltages
Please note that LED components are not considered bulbs, an LED bulb is a complete system consisting of LEDs, LED drivers or resistors, and a housing.

DO NOT use LEDS without a current limiting resistor in series with the LED. The forward voltage rating is TYPICAL and can vary from part to part, so while some LEDS may work fine just connected to a battery of the proper voltage, others will be overdriven and be destroyed.
ALWAYS USE A RESISTOR IN SERIES WITH THE LED OR LEDS

First I loved your article.  Enough so that I'm planning lighting as I build structures.

I'm looking at the dimmer board.  How did you determine the size of the common resistor?  What's stumping me is how to anticipate an unknown quantity of LED's.

Thanks

Scott

Scott,

First, although I answered your question about the dimmer, I did not write the article, Ken Ferguson wrote this fine article.  If Ken is following this discussion, maybe he will chime in with better answers and information.

I use an online wizard (the same one that is linked from the Superbright Site) to calculate resistor values etc.  Wiring LED's in series you have to allow enough voltage for each LED and for the current limiting resistors in the circuit.

The dimmers from Superbright seem to be intended for LED BULBS that operate with a supply of 12 Volts DC already.  In the case of model lighting we are usually using component LED's which will only tolerate a few volts and about 20ma of current.

What is your intention for the dimmer?  To dim all of the LED's on the layout?  To dim all LED's in one structure?  How many LED's do you anticipate powering?  How many will you want to have controlled by a dimmer?

Play around with the array wizard and see what it advises.  For example I entered the following numbers;

12 volts source voltage, 2 volts diode forward voltage, 20mA diode forward current, 100 LED's in the array.  I chose to have the wizard show wiring diagrams for the array.  The best solution indicated 20 groups of 5 LED's wired in series with a 100 ohm, 1/4 watt, resistor for each group, connected in parallel with the 12 volt power supply.  The array would draw 400 mA of current from the supply.  Following my general rule of not loading a supply beyond %80 of maximum rated load, I would need a 12 volt supply with a rated output of no less than 500mA.

Hope this is of some value to you.

It's actually two different issues.  The first one, I was curious.

I have been playing with the calculator at Super Bright LED.  Been having fun actually.

The interest in Ken's Dimmer Board is the same as the reason he was building it.  I would like to play with the resistances to see what the lighting actually looks like in different bildings without having to play musical resistors. The common resistor is intended as a safety to prevent cooking of the LED's.  If the number and type of LED's is unknown, what would the common resistor be? 

I think I may have come close to an answer.  On my layout most of the lighting will be yellow 3mm LED's.  I'm in N-Scale and most of the lighting would be oil lamp or single bulb.  If I set the common for one LED it would throw off the amount of light if there are more than one light.  But if I set it for the largest number likely to be used, wouldn't leave things unprotected if there is only one bulb?

Scott

Actually, if you are not using LED's with identical specs, you should use a series resistor for each LED I believe.

Determining the resistor value for an array without knowing the quantity and specs of the LED's is virtually impossible...at least for me it is! [grin]

I have used LED's for many years and have found, most for our use are 20ma, max. I usually run most at 10 ma but some at 15ma. I always stay at 75 percent of the rating for electronics circuits. For used wall warts, 50 percent max.

You can see some difference in brightness with say a 1000 ohm potentiometer but keep the resistance above 500 ohms.

Also, LED's have different brightness depending on the color using the same current.

I normally use one resistor to one LED. For a number board loco, two LED's max. I don't worry about the voltage rating in this case.

Inverted cone LED's are also very good for structure lighting.

Light bulbs are definitely better for variable lighting.

I use a 1.2mm, 1.5 volt bulb connected to an old FM radio ear phone output to simulate an arc weld. I coat the bulb with a little blue highlighter to give the bluish arc. With some fiber optic and red and orange LED's, you can put the fiber optic around the arc to simulate sparks. I do this with a micro processor IC for timing of the sparks.

A super bright LED would work very well also.

I did the below measurements sometime ago.

LED Resistor Values

Measured with 12.2 VDC supply using 20 ma max current LED's. Values will vary some depending on actual DC supply value.

Resistor Current

1000 ohm 9.0ma

750 ohm 12.45ma

680 ohm 13.12ma

510 ohm 16.25ma

My latest project is a lighthouse with an inverted cone LED and a electronic circuit to simulate to a rotating beacon. The beacon does not really rotate but the brightness changes, simulating a rotating beacon fairly well.

Rich

Moderator Edit:  Fixed formatting issues with text pasted from Open Office or MS Word.  Try using the "Paste From Word" button on the toolbar to see if it works well with Open Office.

I just got back from doing the same thing that Rich posted above.  It is somewhat redundant but here it is all the same.

Power supply is 12.37 Volts DC.  I used six identical 3mm yellow LED's for my tests.

3.9K ohm - 2.5mA

1.5K ohm - 6.9mA

1K ohm - 10.3mA

820 ohm - 12.4mA

560 ohm - 18.5mA

270 ohm - 38.3mA *

*note in this instance the LED heats noticeably and the resistor gets quite hot.  I was amazed that the LED lasted through the tests, I assumed it would blow fairly quickly with nearly double the maximum current passing through it.

What I determined from my test is that the brightness of the LED's did not change dramatically with the changes in resistance.  Yes, the LED with the 3.9K ohm resistor was noticeably dimmer than the rest,  and the LED with with the 270 ohm resistor was noticeably brighter, but the rest sort of fell into the same range of luminosity from what I could see.

I have to agree with Rich that incandescent bulbs are better suited to variable lighting applications.

Here is a picture of the test subjects, from left to right, brightest to least bright.

I had bought some LED's online (down by d'Bay) and they sat on my "someday" shelf.  Well today was one of those somedays.  After reading your article I thought I'd give it a go.  I have 200 LED's & matching diodes so if I fry a few it will be a lesson learned. 

None fried, two LED's shining brightly.  Very bright indeed.  Use a 9 volt battery to test them.  Can I use an old DC tranformer to run these lights - vary the voltage to dim the lights? 

It will take time and practice to get good at it, and quicker, but with the first two under my belt I'm ready to light up some of my buildings with LED's instead of GOW bulbs (mind you I think I have a package of 100 of those in one of these wee parts bins. 

I have not yet put up any window dressing, but looking into the building I can clearly see the glowing LED.  I cut down a pill bottle and will use it to diffuse the light, may need to paint the plastic? 

Any tips on how best to attach these things to the wall or ceiling.  Not having much luck with styrene glue or AC glue.  Have the LED's poking through a hole I drilled and have them tapped in place to give the glue time to cure. 

By all means use an old 12V transformer. I use an old MRC throttle to power mine. The nice thing about old throttles is you can vary the intensity of the light and if you have different buildings hooked up to different throttles, then all of the buildings in one area won't have the same brightness.

Roy

I would use LED's for my buildings but never thought the color looked right, especially since I model the mid '60s on my railroad.  So, I use incandescent bulbs (12, 14, and 16v), and operate them at less than their rated voltage for three reasons; one is they give off a warm yellow glow like back then, second they run cooler that way, and the other reason is that they last much longer.  In 12 years I've had to replace only one bulb out of the hundreds I have.

John

I like to use warm white LEDs for lighting.  The cool white LEDs have a slightly blue color.  The blue is especially apparent if the voltage is reduced to dim it.  The warm white LEDs have a slightly yellow color that mimics incandescent lights.  I recently found a good source for warm white LEDs - Christmas lights!  BE SURE TO GET WARM WHITE!  I recently bought a 200 light string of warm white Christmas lights at Sam's Club for $21.23 with tax.  Because there are 202 LEDs (2 spares), the cost is 10.5 cents per LED.  The light bulbs have to be taken apart to get to the LED.  The actual LED is about a T1 size.  The LED has an inverted cone lens that reflects light in all directions instead of only out of the top.

Darrel

Has anyone ever used this. The catalog says it can be used to light a number of buildings, 2 and 3 story.

http://www.walthers.com/exec/productinfo/475-100IBL01

Sounds okay but I would like feel better about spending 40 dollars.

"The LED has an inverted cone lens that reflects light in all directions instead of only out of the top."

Can you post a pic of an individual LED?. TIA.

Looks like a common 5050-150 LED strip to me. Whole lotta' money for so few LEDs.

Sorry to take so long to respond to the request for pictures of the inverted cone LEDs.  I am retrofitting lighting into all of the buildings at the Greeley Freight Station Museum (www.gfsm.org).  For this project, I needed to mount the LED on a small piece of perforated circuit board.  "A" in Fig. 1 is the "bulb" as is was remove from  light string.  "B" is the disassembled "bulb" - the green part has to be cut open to disassemble the "bulb".  Wires can be soldered directly to the LED but I preferred another method.  "C" shows the LED and the perf board.  "D" shows the finished assembly.  Unfortunately, the inverted cone part of the LED does not show up very well but it is just as the name implies - an inverted cone.

Fig. 1

Eventually, we will want active building lighting - individual controlled lights in each window of each building rather than passive building lighting - a single light bulb inside of each building (glowing building).   Because the vast majority of buildings that I am lighting were not designed or built with interior lighting in mind, I had to come up with an easy way to add lighting each building.   Instead of trying to build a detailed interior for each building, I chose to concentrate only on a small area just inside of each window.  I developed a small window box that is glued to the inside of the window.  These boxes are cast in black resin so they do not need to be painted.  "A" & "B"  in Fig. 2 show the LED/perf board and how it is glued to the box.  "C" shows a baffle that is glued in place to prevent a bright spot above each window.  "D" shows the completed window box ready to be glued into a building.  An added bonus is that you can no longer see through buildings.

Fig. 2

Darrel

I have developed a simple circuit with a Quad IC Timer that will allow various lights (rooms)  in a structure to turn on and off.  I've torn open some buildings to rewire the single circuit in the original, into several by room.   Having just finished the "Wall Dog" story in the current issue, I am behind on putting the timer into place on the layout to test it.  Within the next couple of months, I hope to post an article on this simple electronics project.

Ken