I googled this question before posting here - I cant seem to find anyone with my exact needs, so I am asking here.

I have a light switch connected to an outlet that is under my house. From here I have a power strip mounted to the joist then there are 3 sets of Home Depot brand landscape lights connected to this strip (22 total lamps). They are too bright, and I would like to dim all three permanently (meaning set it once). I don't have any desire to change the level once I have it set, so its okay if the device I need is under the house.

What should I do?

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    Why don't you just swap the lights themselves with some lower wattage replacements? May probably be cheaper in the long run, too. – alt Mar 4 '14 at 21:39
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    Hang on, you have a POWER STRIP mounted to your joist? Is it exterior-rated? Can it withstand rain / snow / whatever else is thrown at it without causing untold misery? – alt Mar 4 '14 at 21:40
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    Sounds like the transformer you have can't be dimmed, which means either replacing the transformer, or dimming downstream of it (before the lights). This might actually be a better question for Electrical Engineering(electronics.stackexchange.com); essentially: How can I dim 22 (LED/incandescent/halogen) bulbs that draw (number of watts) watts each at 12V AC? – gregmac Mar 4 '14 at 22:34
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    Sounds like a Variac would do the job: google.com/… – Wayfaring Stranger Apr 4 '14 at 21:31
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    A variac would be the way to go, reducing the input voltage but still providing a sine wave. This is if you have a straight transformer not a switching supply. – Ed Beal Mar 19 '19 at 21:25

The specifications for the current power pack (transformer) offered by Malibu says that it is Not for use with dimmers. Older versions listed on their site also say the same thing.

While some of the earlier transformers from that manufacturer may differ, it doesn't look promising unless you swap out the transformer for a different brand.


I had the same problem when I replaced an outdoor landscape spotlight with 5W it could signal aircraft to land way too bright. I took a small piece of solar screen 90% and I cut it around the round lamp face and pushed it in. now it is perfect, if it was still too bright I could put another screen on top of that but just the one was perfect for my use. LED's are much cooler and they do not generate much heat.


The easiest thing to do is just replace the lightswitch with a dimmer switch. They make ones where the switch is separate from the dimmer so you can set it to the desired level and then just switch it on and off. If you want to lock in the dimmer, just use some superglue.

  • and this is safe on low voltage landscape lights? – AlanL Mar 4 '14 at 21:02
  • Good point. You will have to check the transformer to see what it says. It's possible it's not dimmer compatible. Another option is you can replace the transformers with ones that built-in dimmers. – longneck Mar 4 '14 at 21:08
  • its a Malibu Low Voltage from home depot. spec on their www don't mention dimmers either way. – AlanL Mar 4 '14 at 21:16
  • You would probably need a magnetic low voltage dimmer in this case – Steven Mar 4 '14 at 21:49

If there are an even number of lamps, and you want them to be a lot dimmer, you could divide them into two groups, with the lamps in each group wired in parallel, but the two groups in series with each other. Note that if any lamp fails that would cause all the other lamps in its group to become brighter and those in the other group to become dimmer. If the lights were near rated voltage after having been wired in series, having the lights that were in the same group as the failed one get brighter could cause a cascading failure, but if each bulb is rated for the full circuit voltage that shouldn't be a problem.

Note that the transformer and all equipment should be perfectly happy with this approach, but that it will probably cut brightness by 75% or so [it will probably cut power consumption by somewhat less than 75%]. Whether that is acceptable would depend upon your desired look.

This particular site doesn't support a schematic-drawing tool, but it would be possible to wire a double-pole double-throw switch to select between normal and greatly-reduced brightness. Such a design would not be appropriate with 120VAC, but shouldn't be a problem with low-voltage wiring.

  • In series if 1 lamp fails the string goes out not get brighter. – Ed Beal Mar 19 '19 at 21:23
  • @EdBeal: Sorry I wasn't clear that the lamps within each group should all be in parallel. If filament resistance was a constant 100 ohms and there were e..g two groups of four lamps running off 14V, then with all lamps intact each group would get half the voltage, or 7V, and have 0.28A (1.98W) flowing through it, with each lamp getting 0.07A (0.49W). If one lamp fails, its three group-mates would have 8 volts across them and pass 0.08A (0.64W) each (total 0.24A; 1.92W) while the four lamps in the other group would have 6V and pass 0.06A (0.36W) each (total current 0.24A; 1.44W)). – supercat Mar 19 '19 at 21:31
  • Ok series parallel then only the ones in the branch with a failed light would go out. But remember lamps are not truly Lenora with respect to there light output and some lamps if run at a lower than rated voltage will have a shorter life a incandescent will last longer. – Ed Beal Mar 19 '19 at 21:37
  • @EdBeal: I'm not talking about a parallel collection of groups made up of series-wired lamps, but a series collection of groups made up of parallel-wired lamps. Brightness is indeed non-linear with voltage, which is why I suggested that brightness would be cut by 75% or so, while power would be cut by less than 75%. – supercat Mar 19 '19 at 21:40
  • Series parallel is the proper term you have a combination. – Ed Beal Mar 19 '19 at 21:58

A variac would be the way to go on the input of the power strip that feeds the lights with a straight transformer. Dimmer's affect the wave form and may cause the transformer to overheat. A variac is a variable transformer that can reduce the voltage without affecting the sine wave. Transformers like this are simple 10:1 step down transformers. If you provide the transformer with 90v AC using a variac instead of 120v now your voltage at the lights would be 9v. Dimmers affect the wave form and create harmonics that can cause overheating this may be why it says not for use with a dimmer. If incandescent it will make the lamps last longer but some xenon and halogen need there rated voltage or the lamp life is shortened.

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