LEDs and Structure Lighting

[Anonymous]

Hello!

How does one go about using LEDs to light the interiors of structures, etc? I'm in the process of building a new layout. My old one had so many grain o' wheats, I needed thre separate circuits + transformers.

I know LEDs need resitors and have to be wired a certain way (AC or DC supply?), I just don't know where to start or what type of LEDs to use, etc.

Thanks in advance!

Matt

[Anonymous]

There is a related issue. There is a recent ad for "AC compatible LEDs" which purport to be simply plug in repacements for standard 12 to 14 volt incandescent bulbs such as those in Lionel switches. Does anyone have wisdom and/or experience with these LEDs?
Ken M.

[Anonymous]

Using DC current, the LED will only light if the polarity is right. I think the long leg is the anode or positive. It doesn't hurt the LED if its wired backwards as long as the voltage is low. You can wire a larger resistor for sevral LED's however if an Led blows the others will get brighter as each receives more electricity. I think it is best to use a resistor for each LED. The resistor sizing determines the brightness of the LED. I have a variable resistor(adjustable) that I wire to a LED then use it to get the brightness I want. Then I measure the resistance set on the varable resistor with my multimeter. I match up a fixed resistor to this reading. It doesn't have to match exactly. I have used 2 resistors soldered end to end to the LED to get the right brightness. You simply add the resistance values together to get the total resistance. I hope this will help. I personally prefer LEDs because they give off less heat and last longer if the resisor is sized right.

[MisterBeasley]

Remember that LED's produce a very directional beam, much like a headlight. If you just plop one down in the center of a building, it will throw light only in one direction. If you point it up and you have a white ceiling in the building, you should get good indirect light.

A big advantage of LED's is that they use very little power, so they run very cool and won't overheat inside a building. They will generally last forever, too. Still, I prefer the warmer, omnidirectional look of incandescents for my buildings.

[Seamonster]

Just a few notes on LEDs.

They want DC. You could make them run on AC if you put a diode in series with them. There are some 3 colour LEDs that shine red with one polarity of DC, green with the opposite polarity, and a sort of yellow with AC.

LEDs are not that good for area lighting. Their light output is pretty directional, although there are some that have a wide diffused output. Bouncing the light off a white surface like MisterBeasley suggested might just work.

Most LEDs are rated at around 2 volts and 20 mA (milliamps or thousandths of an ampere). Don't worry about the voltage. You can operate them on any voltage above 3 volts with the proper resistor in series with them.

It's easy to calculate the resistor size needed. Subtract 2 (the LED voltage) from the supply voltage. Divide that answer by 0.02 (for 20 mA). Use the next largest standard resistor size. A 1/4 watt resistor is fine for one LED. Example: to operate an LED from 12 volts: 12-2 = 10. 10 / 0.02 = 500. The next largest standard resistor size is 560 ohms. So use a 560 ohm, 1/4 watt resistor in series with it.

You can operate LEDs with much less than 20 mA. I've found that at 15 mA I can't see any difference in the light and that's what I usually run them at. If you want less light, run them at less current (higher value resistor).

The long lead is usually the positive lead. I say usually because I bought a bunch of yellow LEDs that had the long lead as the negative one. If it doesn't light up when you connect it, just reverse it. You won't damage the LED by reversing it so long as you have the proper size resistor in series with it.

The resistor can be attached to either lead.

Each LED needs to have its own resistor. Don't try to run a bunch of LEDs off one dropping resistor unless they are individually switched and only one will be lit at a time. Then you can put the resistor in the common lead of the bunch.

Hope this helps. There's no big mystery about using LEDs and the resistor calculation is easy. However, like MisterBeasley, I too prefer the warmer look of incandescent lamps in buildings. I use 12 volt GOW bulbs and run them on 10 V.A.C. The reduced voltage makes them last a heck of a lot longer without appreciably reducing the light output and since incandescent bulbs don't care if they have AC or DC, it saves making a high power DC power supply. Also, at 10 volts, the bulbs are barely warm to the touch even after hours of operation, so they won't be a threat to my plastic buildings as long as the bulb doesn't come in contact with the plastic.

[Anonymous]

Hi Pensy Man,

Please try this link.
Hoping it will help you.
http://www.merg.org.uk/index2.htm

Kind regards,

Andre Ingels
Brussels, Belgium (The beer country[:I])
"C&O, the way to go"

[ATSFCLIFF]

LEDs with correct resistors are long lasting but are not bright for structure lighting. Mini bulbs are better. If you are using power from your 12v AC outlet from your controller,use bulbs rated 9 - 12 volts. The bulbs will not be overly bright and they last very much longer.

Cliff

[scubaterry]

I am working on putting four LEDS in a dual track signal bridge. I will be wiring them in series so every other led is green and of course the ones in between will be red. My question is if the LEDs are in series will they require only one resister?
Terry

[Anonymous]

As I've posted before, the newer, smaller Surface Mount LEDS are excellent for structure lighting because of their "top hat" shape. They diffuse light much better than the traditionally shaped LEDs which are very focused. Yellow is a good choice for home lighting. Mounted from a ceiling location, they provide plenty of light for a room.

They're readily available from sources like Digikey and Mouser. LC-LED.com's bright white SMD is great for mimicing flouresent lighting in businesses.

Each manufacturer's "yellow" tends to be slightly different, so mixing brands within a house looks pretty good.

The only drawback is that you have to solder the wires to the very small rectangles on the back of the LED. The first couple of attempts can be daunting, but it gets easier with practice.

Mike Tennent

[tsasala]

Wiring LEDs in series only requires one resistor, but the value changes due the voltage drop across each LED. You can probably wire them in parallel and use one resistor if the resistor is before the network. However, that increases the current draw while leaving the voltage the same. Either solution modifies the resistor value as the voltage or current changes (V=I*R or R=V/I)

Diffuse lense LEDs are not as directional as clear lense LEDs. Most head light LEDs are clear lense. There was a time when they only made diffuse lense LEDs.

I like the SMD idea, but wiring is tricky depending on the packaging. leaded chip carrier packaging would be easier to solder then leadless carriers.

-Tom

[tsasala]

Oh, the length of the leads is not a 100% indicator. There will always be a flat side on round LEDs (e.g., T-1 3/4, T-1), which indicates the cathode (negative) terminal. SMD components will have one of the corners marked, usually with a bevel or diagonal.

-Tom

[Anonymous]

As always, I know I can count on the gang here for help! Thank you very much. I have been educated.

[meldridge]

You don't need a diode to use LED's with AC. The D is for diode. On AC the light is on half the time, yielding half the light it would on DC. Also, different LED's have different current ratings. The red ones are generally 20 mA, but the green and yellow are often 15 mA. Some of the white LED's take 30 mA. You have to check the specs to determine the correct resistor to use. Since resistors cost about two cents, there is no reason to try to use one resistor for multiple LED's; it will just cause problems.

[Anonymous]

To clarify this I am a design engineer for MPLX ELECTRONICS SYSTEMS. I work with LEDs on just about every project I handle. Here is what you need to know:
1. LEDs are directional in terms of polarity. The cathode is connected to ground and the anode is connected to V+. The cathode can be distunguished by a flat mark on side (T1 and T1 1/2 cases). For SMD LEDs, there is a similar approach. LEDs work fine on AC. The alternating current that most modlers come across is 60Hz. or DCC which is in the low KHz. If you are apt, take a LM555 IC and configure an oscillator with a pot. Adjust that pot. You will get a variety of frequencies. Observe the LED and you can see that if at a low frequency (somewhere around 30 Hz.), you will be able to see the flicker in the LED and if you adjust it low enough, you will see the individual pulses. At a minimum frequency of 60Hz., which is what the average moder sees, your eyes cannot see the rapid turning on and off. This is how you can get by with the appearance of continous light. THis applies to ALL lights working on AC.

2. Current limiting resistors are a MUST above appx. 2 V. Here is the formula : V+ minus VLED divided by IF where V+ is your power supply voltage, VLED is the rated operating voltage and IF is the rated operating current.

3. LEDs have a mcd rating. This is millicandellas which is a measure of luminous intensity. The higher, the brighter. However, LEDs such as this are NOT always rated ~ 2V 0.2mA and often a higher IF.

4. LEDs to have a small degree of emmision. I suggest getting one with a large viewing angle or using paper or foil to spread light as you desire.

[mrunyan]

As far as viewing angle goes, the normal plastic bodied, leaded LEDs have their limits, yet there are simple ways to diffuse their light by sandind the sides of the lens or diffusing screens. But consider the new surface mount chip type LEDs they are a small but bright source and spread light even out their sides, virtually 180 degree spread although not evenly distributed of course but way beyound the 30 to 40 degrees of typical leaded ones.