LED lights on a dimmer

[Marcel Birgelen]

A "traditional" SMD LED uses internal gold wires to connect the surface connectors to the LED, a CSP LED eliminates the internal wiring and the LED substrates are mounted directly on the underlying PCB surface.

CSP LEDs should have better heat-conductivity and the lack of internal wiring should make them more robust and increase the light-emitting surface compared to an SMD package...

I don't know why they choose the confusing naming, as both the SMD and CSP packages are both "Surface Mount Devices"...

[Steve Guttag]

CSPs are within the SMT family. SMT merely denotes the method of attachment. CSP denotes the size and how it relates to its die. You can have many different packages within SMT but they would not be CSP.

[Mark Gulbrandsen]

It's funny how they coined "chip scale package" when all it really is is SMT.

[Steve Guttag]

No, the Eprad system is proprietary. Their LED driver module only works with LED lamps and vice-versa. They are using low-voltage DC to the lamps but us existing wiring infrastructure. As for Kelmar's dimmer working with a lot of lamps...they can. We have traditionally speced only Kelmar dimmers but the lamp consistency in the field, even getting the same make/model lamp was horrible. Maybe Cree has held their manufacturing/supply to be consistent. I have not had issues with Cree, in general (or Fiet) but forget brands like TCP. They are supplying whatever is cheap from China that month. They may work, they may not.

At least with the Eprad system, you have something that is going to work from batch to batch and lamp to lamp and it will dim like an incandescent rather than like an LED, in terms of its dimming curve. Most LEDs compress their light output to the bottom 30% of their range. One nice thing about the Eprad dimmer is that you can set the level and fade rate numerically rather than with a trimmer so it is very repeatable.


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[Mark Gulbrandsen]

One of the problems we've found is that even buying the same manufacturer and model of lamp (same part number) can get you an entirely different lamp with completely different dimming (or lack thereof) properties. Hopefully, Kailin will continue to supply the same lamp for you and your needs.

We are now recommending, for cinemas, the Eprad lamps/dimmers since they make both A19 and PAR38 lamps and they make a retrofit module for existing dimmers to work with their lamps. So far, no complaints.

But do they work with any other brands of lamps? I certainly would not want to be stuck with a lot of pieces of equipment that can't work with others. No complaints about the Eprad dimmers, but the Kelmar dimmer will work with about 8 different types of commonly available LED lamps. In fact I always found CREE to be the most consistent and they can be bought in several temperatures and at a zillion places.

[Steve Guttag]

One of the problems we've found is that even buying the same manufacturer and model of lamp (same part number) can get you an entirely different lamp with completely different dimming (or lack thereof) properties. Hopefully, Kailin will continue to supply the same lamp for you and your needs.

We are now recommending, for cinemas, the Eprad lamps/dimmers since they make both A19 and PAR38 lamps and they make a retrofit module for existing dimmers to work with their lamps. So far, no complaints.

[Jim Cassedy]

Time to drag this topic bak into the light of day again! I recently moved into a larger ( and horribly more expensive) apartment in my building. There were a couple of lighting fixtures that I wanted to put dimmers on, and I've discovered some cheap LED bulbs that are 100% indistinguishable from incancescants when put on a dimmer.

They go from full 'off' off to full 'on' with absolutely NO sudden turn-on or turn-off point when used with the standard LUTRON residential dimmer switches you find in Home Depot, & elsewhere. They even work without flickering on the bare-bones dimmer circuit in a cheap table lamp I have. I spent quite a bit of time trying to figure out how they accomplished this, even hooking them up to an ammeter & o-scope to analyze current flow, and I think I've figured out that the "trick" is that the bulb globes are coated with very slow responding phosphors. So, although there are actually "on" & "off" trigger points as in regular LED bulbs, you never see them because the phosphors take probably 500ms or more to respond. So the effect is a gentle "ramp-up" of brightness when you turn them on, and a slow decay to dark when you approach full the full dim setting.

I'm not even sure where I originally got these. Most likely I picked them up as spares while shopping in Chinatown a couple of years ago. I wanted to buy a few more when I realized their dimming properties, and they are tricky to find online unless you want to buy them in wholesale quantities. However a friend in construction was able to pick up a ½dozen for me at a local contractor's lighting supply house here in the Bay Area. I think they're only made in this one size, so I don't think you'll really find any auditorium applications for them- - but if you are looking for an LED bulb with 100% incandescent emulation on a dimmer for home, hallways, projection booths & control rooms, etc, these might be worth tracking down. A neighbor saw mine & was amazed enough by their dimming properties to track a couple down for his TV room. He luv's 'em too!

They are KAILIN - KLL760P-9
Standard USA E-27 / A-19 configuration
120V/60hz / 9watts / 805 Lumens / 2700°K
KailinBoxAndBulb.jpg

>Decoding the phone number on the back of the box
appears to place the factory in Dongguan, China
> A Chinese buddy tells me that KAILIN is probably
a westernized version of "kai lin", a Chinese name
which, roughly translated means "pure"

[Randy Stankey]

The LEDs in the stairway lighting at Mercyhurst were connected in alternating fashion.

When I first started there, they had those plastic tubes with "grain of wheat" lamps inside them attached to each step.
From the day I first walked into the place, I told the boss that those lights weren't safe and that somebody was going to fall down and get hurt in the dark. Of course, my request was roundly ignored until some old lady fell and twisted her ankle. It happened on a Saturday night and my boss was asking me to get quotes for installing the correct lighting, on Monday.

Anyhow... I got quotes for the DC version power supply so that the lights would be dimmable but, of course, they overrode me and got the AC version power supply.

Yes, every time I walked up or down those stairs, I could see them flicker out of the corner of my eye!

Bugged the crap out of me!

I did record them with a video camera and that's how I discovered that they were wired in opposing series-parallel sets.

So... Yes... I know that "good" Christmas tree lights (or other kinds of LED lights) can use a cheaper AC version of power supply or the better DC version. But, I assumed that you were talking about AC because you mentioned about the flicker.

That's why I replied the way I replied.

[Lyle Romer]

I think you're right but I also think that they might be series-parallel, having two strings of lights in series connected in parallel so that the diodes are going in opposite directions. That way, one of the parallel strings is always conducting so that all of the sine wave gets used.

You'll still be able to see the individual lamps flicker but, if you slow it down, you'll notice that half of the LEDs are lit and the other half is dark.

There are several segments (unless they are very short strings) and each segment looks like just a bunch of series LEDs in series with a resistor. The segments are parallel but I don't think they bother reversing polarity on every other segment.

It's basically (a very crude text based schematic):

|-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-|
|-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-|
|-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-|
|-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-|

When stretched out it turns into

|-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-||-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-||-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-||-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-D-R-|

There's basically a hot wire and a neutral wire that run end to end (but physically have connections on larger sockets) and then each series segment is connected in parallel via the same larger sized sockets. If you untwist the string you can see the way it is connected.

[Mark Gulbrandsen]

A little more info -- we have six or eight spotlights that flood the screen before the show (in place of curtains) so those are on the dimmer in addition to the regular house lights. We have one extra outlet tied into the same circuit as the stage lights, so that's where I plug in the Christmas lights. So, there is already an incandescent load on the circuit. The spotlight bulbs are #4515 which are a 6-volt bulb -- each of the light cans has a step-down transformer in it. They are leftovers from my days as a dance-floor DJ.

The light string that has quit has a weird looking fuse that I've never seen before - it looks like a letter H, plastic, with filaments down both sides. I'm sure it would be cheaper to just replace the lights. I may just find a spare set of LED lights and give it a shot.

The dimmer is one that has two circuits -- a "house lights" circuit and a "stage" circuit, so these lights and outlet are wired to the Stage side. The circuit is never left "half on," it's always full-on or full-off after a dim cycle.

Mike, Call Tom at Kelmar and he should be able to tell you all compatible lamps that work with their dimmers. (631) 421-1230

[Leo Enticknap]

Some cheap versions work like that, others use a DC power supply. I have seen chains with 4.5VDC and 34VDC, but, technically, they can be made in a big variety of schemes.

Our Christmas tree lights are powered through a 5 volt, 4 amp DC wall wart. Haven't tried dimming the input power, though. Might do for a giggle when we're taking the tree down on Sunday - I have a plug-in dimmer (intended to enable a table lamp to be retrofitted with dimming capability) in a box of crap in the garage somewhere.

[Mark Gulbrandsen]

I have many customers running LED on Kelmar dimmers. The Cree works fine without any modifications to them at all. But if you use other brands Kelmar has at least one option available.

[Carsten Kurz]

Some cheap versions work like that, others use a DC power supply. I have seen chains with 4.5VDC and 34VDC, but, technically, they can be made in a big variety of schemes.

[Randy Stankey]

[QUOTE=Lyle Romer;n8011]

... I'm pretty sure the Christmas light strings are just a bunch of LEDs in series with a resistor as a current limiter in series. ...
... If I stare at them in the right conditions I can easily see the 60 Hz flashing because they are only on for part of half of the sine wave.../QUOTE]

I think you're right but I also think that they might be series-parallel, having two strings of lights in series connected in parallel so that the diodes are going in opposite directions. That way, one of the parallel strings is always conducting so that all of the sine wave gets used.

You'll still be able to see the individual lamps flicker but, if you slow it down, you'll notice that half of the LEDs are lit and the other half is dark.

[Lyle Romer]

It most likely won't damage the dimmer, but depending on the led light string's voltage drop circuit for the LEDs. that dropper may not like the dimmer much. Only way to find out is do a test, first find the dropper circuit (often in what looks like a socket but with no led in it), then power the string though the dimmer and make sure that dropper doesn't get more than slightly warm. I think most led strings would be ok, but might behave oddly during the dim up/down phases.

If that outlet is the only thing on the dimmer, to avoid the LED string from flashing during the dim up/down, you may need to add a small amount of incandescent load to it.

I haven't really done any teardown or measurements but I'm pretty sure the Christmas light strings are just a bunch of LEDs in series with a resistor as a current limiter in series. They are done the cheapest way possible. If I stare at them in the right conditions I can easily see the 60 Hz flashing because they are only on for part of half of the sine wave. They aren't designed like an LED bulb or decorative LEDs designed for dimming control.