LEDs Dimmable?

[CNE Runner]

I'm sure you have noticed the plethora of LED replacement 'bulbs' at your local home store. The Monks' Island Railway uses two track light units (with 3 lights in each track) for lighting. Both of these tracks are run through a dimmer switch ('really makes switching interesting when simulating just-before-dawn with the lighting). A problem with these halogen lights is the considerable amount of heat they produce.
My local Lowe's had a demonstration setup of various bulbs and their LED replacements. I was struck by the tremendous difference in generated heat between the halogen bulbs and their LED replacements.

Some of the LED units were marked 'dimmable'...unfortunately the bulbs I require (GU10 I think) were not. My question is: Are all these LED replacements dimmable?

As always I await your wise guidance,
Ray

[richg]

I'm sure you have noticed the plethora of LED replacement 'bulbs' at your local home store. The Monks' Island Railway uses two track light units (with 3 lights in each track) for lighting. Both of these tracks are run through a dimmer switch ('really makes switching interesting when simulating just-before-dawn with the lighting). A problem with these halogen lights is the considerable amount of heat they produce.
My local Lowe's had a demonstration setup of various bulbs and their LED replacements. I was struck by the tremendous difference in generated heat between the halogen bulbs and their LED replacements.

Some of the LED units were marked 'dimmable'...unfortunately the bulbs I require (G10 I think) were not. My question is: Are all these LED replacements dimmable?

As always I await your wise guidance,
Ray

LED's must be dimmable. Bachmann does it to their steamers. I have a couple and many here have commented on them.
Below are some numbers you can work with. Take say a 1,500 ohm or 2,000 ohm pot in series with the LED and experiment. When you get the intensity you like, measure the resistance of the pot. I would keep a 510 ohm resistor in series with the pot in case you turn the pot too low. Keep that vlue in mind when you do the matth.

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

A couple of my Spectrum's had somewhere about 2,700 ohms I think on the factory equipped PC board which resulted in about 5 to 6 ma of current. I use the NCE Power Cab which results in about 12.3 volts DC for the lighting circuits out of the decoders.
Different makes and colors of LED's can have different intensity with the same current.

Rich

[Jim Banner]

All LED's are dimmable if you change the dc current flowing through them.  This can be done with either a variable current power supply or a variable voltage power supply.  With the latter you use the usual ballast resistor, then as you change the voltage applied to the LED/resistor pair, you are again changing the current through the LED.

Unfortunately, the dimmers designed for use with incandescent lamps do not work this way.  They work by turning the current on and off every half cycle of the 60 HZ ac power fed to them.  The earlier in the half cycles that the power is turned on, the greater the average power fed to the lamp and the brighter it is.  Conversely, the later in the half cycles the power is turned on, the less the average power fed to the lamp and the dimmer it is.  At the end of the half cycles, the power is turned off.  This method of dimming works because incandescent lamps have filaments with thermal inertia, that is, they stay hot from one half cycle to the next even when the power is being turned on and off 120 times a second.  If you have ever noticed the after glow when an incandescent lamp is cooling off right after you switch it off, you have seen this thermal inertia in action.

LED's don't work this way.  They can turn on and off thousands of times a second.  So with a regular lamp dimmer, they turn on and off again every half cycle.  We don't see this because our eyes cannot see flicker that happens 120 times per second.  Our eyes see the LED's as being on continuously even though they are not.  But our eyes don't see the average brightness over each half cycle, they see the peak brightness.  So whether the LED's are on for the full half cycles or only come on half way through each half cycles makes no difference to our perception of their brightness.  Turning the LED's on still later in the half cycles will dim them as can be shown with a light meter.  But our eyes have a logarithmic response to light so that this dimming is barely perceptible until the LED's turn right off.  The bottom line on this is that instead of the dimmer knob having a control range of about 270 degrees, the whole dimming action appears to happen in the last 30 degrees or so.

So how do dimmable LED bulbs work?  Typically they contain some electronics which rectifies the ac and then averages the results.  This process is the electronic equivalent of the thermal inertia of an incandescent filament.

The type of dimmer I have just described is not the only type of dimmer available.  But because they are cheap to make, they are widely used.  Another type of dimmer is the variable transformer, often called by the brand name "Variac."  These can dim regular LED bulbs but are an expensive solution.  It strikes me that it should be possible to build the necessary electronics into the lamp socket so that any LED bulb could be dimmed by low cost dimmers.  Unfortunately,  such units are apparently not commercially made which is a pity - they would seem to be a very neat solution to Ray's problem.

Jim

[CNE Runner]

Thank you for the reply RichG and Jim. Rich, I was talking about lighting for my layout (110v AC) and not for my locomotives...I saved your excellent answer for later reference though. Jim: As I sift through your [technical] response, the answer seems to be if the LED box doesn't 'say' Dimmable - then it can't be dimmed. The next step would be to search the Internet for a supplier of GU10 dimmable LED replacement units...these are popular track lighting units and shouldn't be hard to find.

I sincerely appreciate both of you taking the time to answer my question...'saved me a long, cold walk to Saskatoon. Both of you have earned a free pass for a ride on Monks' Island #4 when you are in Nirvana...I mean Alabama.

Cheers,
Ray

[CNE Runner]

I just began my research into finding dimmable LED track lighting bulbs. The first website I encountered had a warning about putting non-dimmable LED bulbs into dimmable service. It can be read at:

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Fbi-pin.html

Enough said.

Ray

PS: I found  a significant quantity of websites that sell dimmable LED bulbs of the GU10 variety and what I found is shocking: they are very expensive. A dimmable GU10 bulb will cost you approximately $33 + shipping! My lighting system has 6 of these 'buggers' - making it all that easier to live with the heat my current bulbs issue.

[richg]

I just began my research into finding dimmable LED track lighting bulbs. The first website I encountered had a warning about putting non-dimmable LED bulbs into dimmable service. It can be read at:

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Fbi-pin.html

Enough said.

Ray

PS: I found  a significant quantity of websites that sell dimmable LED bulbs of the GU10 variety and what I found is shocking: they are very expensive. A dimmable GU10 bulb will cost you approximately $33 + shipping! My lighting system has 6 of these 'buggers' - making it all that easier to live with the heat my current bulbs issue.

Try to keep the LED and bulb terms separate. I have seen in a couple forums, some asking where they can find LED bulbs thinking they are one item.
They are different animals.
One voltage operated, the other current operated which always leads to more discussions.

Rich

[CNE Runner]

'Will do Rich. Again, I thank you for taking the time to answer my query. Anything you write, on the forum, I take seriously and [usually] make a note of its content. I am sure many of us appreciate your knowledgeable input.

Regards,
Ray