[Elecraft] LED Lamps and HF RFI?

[Craig Smith]

You are wise, Ted, to be cautious about this.

As you implied, it is not the LEDs themselves but how they are driven.

LEDs are current driven devices and, for a given intensity, are typically driven by a constant current source.   In the case of a panel LED in a K3 or whatever it is easy to do this by just using a series dropping resistor as an analog current source and not worrying about the lost power in the resistor.    This approach will be quiet in terms of RFI.

In home lighting applications, the currents are higher as are the desires for high efficiency and minimum power loss.   So a switching regulator type of current source is employed, either on a lamp-by-lamp basis or be connecting several lamps in series with one current source.   The switch mode current source can indeed be noisy.   Even though in theory it could be made fairly quiet by means of good layout, control over wave shaping, extensive filtering, and high quality compliance testing, all of that typically does not happen in a cost-driven application such as home lighting.

You asked for people with good data.   Unfortunately, I'm not one of them.   I'm not even sure if good data exits on lighting RFI in a real-world applications.    Even if a manufacturer characterizes the EMI performance in a data sheet, things are sometimes cost reduced later in manufacturing (less filtering) and can also be compromised by improper installation and grounding by a contractor.

Conceptually, I'm a big fan of LED lighting and have several types in various places in the house.    But back when I was active on the air I made sure that I could turn them all OFF easily on contest weekends, etc.

The bottom line is that nothing is quieter than incandescent.  I wish that that wasn't the case as the energy savings with LED are significant.   Perhaps in 10 years it won't be a concern.   But right now I would be cautious and have a "plan B" for lighting when operating.

73     Craig    AC0DS

On 11, May2015, at 8:13 PM, Dauer, Edward wrote:

> Had an electrician at the operating QTH today to discuss replacing the
> recessed ³can² lighting throughout the house.  He suggested replacing the
> incandescent cans (now 65 watts per bulb) with LED lamps (same lumens with
> 10-13 watts per bulb).  I have looked at the Internet on the question of
> RFI from LED bulbs and see wildly inconsistent reports.  It is the case
> that HF radios like the K3 have LEDs in their panels; but I would be
> installing as many as 60 LED fixtures running at 10-13 watts each.  My
> caution comes from my novice days in the 50s when a single fluorescent
> lamp put my hamming out of business - things were quiet when the only
> light source was the filament of a 6146 and the dial lamps on the HQ-100.
> I know that LEDs aren¹t at all the same; but I don¹t want to relamp the
> house if it puts me off the air.  And if they (or their power supplies) do
> generate RFI in the HF bands, would the K3¹s NR get rid of it?  Anyone
> have any good data on this?
> 
> Tnx,
> 
> Ted, KN1CBR