Traditionally Christmas lights were always AC powered using either direct connection to the main (240V) or via a small plug pack power supply. One of the many queries I get is should we go AC or DC for lighting Control. Let’s explore this point further.
For the Purposes of this discussion we will break the type of lights into 2 main categories Low Voltage and High Voltage. Low voltage Lights are any lights, AC or DC, that are connected to a transformer of sorts like a plug pack. the majority of Christmas lights fall into this category. High Voltage lights are any lights that connect and operate directly from 240v Mains. Rope lights are the most popular version of this category
To control lights in a display that both you and your audience enjoy, Safety is paramount. Here is Australia, using mini globes direct connected to mains it not allowed in external displays (for some unknown reason the authorities are still willing to allow people to use them inside where the risk is still high).
A couple of people have tried unsuccessfully to control their low voltage lights by switching the mains voltage. the results were a complete melt down of the plug packs. but hey, step down transformers were never intended to operate on chopped mains.
High voltage lights can still be used in Australia as long as there is adequate protection. I still use rope light in my display due to the strong mechanical characteristics and the the solid colours. With careful technique the lights can be trimmed to length for suit each display item. High Voltage lights require AC Dimmers for control. My 16ch AC Serial SSR is but one example of such dimmers. Available in 24, 36, 48 Vac, they dim lights by chopping the AC voltage supplied to the lights.
Low voltage lights rely on some form of step down transformer to provide isolation protection form mains voltages. Typical incandescent mini globe type lights are an example. these lights are usually AC. However to dim these lights the dimmer needs to be placed between the plug pack and the lights. (You can not dim the mains going into the plug pack – this is not only dangerous but could result in a fire!) My 16ch AC Serial SSR is but one example of such dimmers. Available in 24, 36, 48 Vac, they dim lights by chopping the AC voltage supplied to the lights.
LEDs also fall into the Low voltage category. However LEDs are a “current” device, meaning the way to dim them is by varying the current and not the average voltage like a incandescent mini globe. LEDs as best controlled using a constant voltage that is chopped on and off. By turning the light on and off quickly enough, we trick the eye into thinking a dimmed LED is actually ON all the time. So here is a simple test you can do at home. There are no tools required. I said at home, but I real meant in your car. The occurrence of LED stop lights and blinkers in cars today has dramatically increased over recent time. Next time your in your car, see if you can notice if the lights in front are LEDs of not. You can tell by the bright constant light and sometimes the individual lights. Now for the real interesting observation: see if you can notice LEDs turn off in an instant, where and incandescent globes just , well fade away. It is very noticeable. This reminds me of my grand mother who once said how amazing it is that when she flicks the switch the light instantly comes on. Well we now know that is simply not true, it is not instant there is a finite delay. I wish she was still alive to be able to amaze her again.
So back to the point at hand. AC or DC. Well the real only is that depends on your load. If you are using Mains lights, AC is definitely the way to go. If you are using low voltage, I would say you can use AC for Minis, an DC for LEDs. But you can also you can also use DC for them both too. That is what I do. AC for mains lights and DC for the rest. It keeps things simple.
The other reasons I like DC for my low voltage stuff is SMPS are:
- Significantly lighter than Trannies of equivalent power
- Can be significantly cheaper than Trannies of equivalent power
- Easy to mount in a box
- adjustable on the output
Have a good one!
