I have turned a cheap floor fan into a floor study lamp; i.e. 30cm of 240V 5W a/c LED (under cupboard) strip light facing down on to the desk. These LED strip lights can be easily daisy chained in series to make a long long line of one strip light. The wiring is straightforward using all three live output wires (blue, white and red) from the fan switch to switch one light on. (I have taken the capacitor and resistor out.) I could have used only one wire, but then I would have to press the exact button on the fan switch to turn my light on. The neutral (black wire) and earth wires just pass directly through to the light, as was the case when this was a fan - The fan did not pass the earth to the motor, so I added it.

OK. So, just removed the old fan switch and added 2 on/off a/c switches for 1 or 2 lights on.

Also, as promised, opened up one light to show the rectifier and 24 LEDs. I tried to measure the volt being fed into the LEDs but only shows 1. When switched off and as the large capacitor is discharging I can see a countdown from "20V" down to 0 ish.

similar lights to these, but mine pass the earth as well

No problem. However, I want to use the power buttons (0,1,2,3) of the original fan to turn on 1, 2 or 3 lights, which will be in parallel. But, the problem is how can I use this switch which only has one specific live output for each button 1, 2 and 3.

I thought about (switch at position 2) connecting 2 output wires (blue and white) to two lights respectively and (switch at position 3) all three output wires (blue, white and red) to all three lights respectively - naturally, at switch position 1, only one light would have a live wire (blue); i.e. all lights will have all 3 live outputs connected.

So, the question is, should I use diodes to stop current flowing back to lights 2 and 3 when switch is 1; and diodes to stop current flowing back to light 3 when switch is 2?

Thank you.


proposed parallel original motor with bits

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  • \$\begingroup\$ This picture is similar to my lights, except mine have 3 contacts/wires passing in and out - live, neutral and earth. \$\endgroup\$ Commented Sep 16, 2020 at 21:09
  • \$\begingroup\$ I could also wire them up in series as long as an expert explains which diodes I should use - thinking about it, series is probably better. \$\endgroup\$ Commented Sep 16, 2020 at 21:12
  • \$\begingroup\$ Put that information in your question rather than as a series of comments on your own question. \$\endgroup\$
    – Transistor
    Commented Sep 16, 2020 at 21:12
  • \$\begingroup\$ When you connect the lamps together, they are not actually in series: they are in parallel, like plugging lights into mains sockets where there is a ring main connecting the sockets. Diodes may not work well with AC-fed LED drivers. \$\endgroup\$ Commented Sep 16, 2020 at 21:27
  • \$\begingroup\$ Done - sorry about the mspaint version \$\endgroup\$ Commented Sep 16, 2020 at 21:57

1 Answer 1


You can't use diodes on the AC directly because it alternates.

LEDs are DC operated so at some point the AC current is rectified for the LEDs.


simulate this circuit – Schematic created using CircuitLab

Figure 1. If the lamp has a back-to-back LED arrangement there is no simple solution to your problem.

Note that the circuit of Figure 1 is showing how the daisy-chain through connections are allowing the L and N to run through each lamp but the actual lamps are wired in parallel, not in series.


simulate this circuit

Figure 2. If the lamps have an internal rectifier then they will work on DC.

If you have this type of lamp then the following circuit should work.


simulate this circuit

Figure 3. A circuit that will work with lamps featuring an internal bridge rectifier.

Here SW1 switches on LAMP1. SW2 switches on LAMP1 and LAMP2 and SW3 switches on all three. You need to run individual live wires to each lamp.

If your lamps contain a voltage dropping capacitor internally then this idea won't work as it will tend to block the DC.

  • \$\begingroup\$ Thank you Transistor - would you mind if I opened the light up and sent a photo or two. My problem is a/c - I don't have many issues with DC. The lights are perfect by the way. instant bright light anywhere at 5W (or 10 or 15 or ...) \$\endgroup\$ Commented Sep 16, 2020 at 22:21
  • \$\begingroup\$ Add any information or photos into the original question and we can have a look. Make sure the photos are clear and cropped to the relevant portion. It's bedtime in Ireland. \$\endgroup\$
    – Transistor
    Commented Sep 16, 2020 at 22:45
  • \$\begingroup\$ Nicely done. I'll send you some Christmas string lamps to look at :-) :-). || Some day I must pull one apart and make sense of them - they seem to be arcanely interconnected strings which MUST be quite simple but have resisted my efforts of staring at them long enough plus making basic measurements. \$\endgroup\$
    – Russell McMahon
    Commented Nov 11, 2022 at 9:01

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