Transformer Basics

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Transformer Basics

Low voltage lighting can be intimidating, especially when it comes to choosing the right transformer. To give you the information and confidence you need to succeed in your deck project, we've compiled some transformer facts below. If at any point you need advice or additoinal assistance, let the experts at guide you by calling 1-888-824-5316.

Low voltage deck lighting uses a transformer plugged into a standard wall outlet to convert ordinary household power from 110 volts down to 12 volts. It’s so easy and safe to install that in most areas of the U.S., installation doesn’t require an electrician unless you choose a transformer that hardwires into your electrical system. Nonetheless, always contact your local building department before starting any construction project.

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Why Quality Matters

The transformer is the heart of your lighting system and should not be overlooked. We recommend choosing a transformer based on quality, not just price, for several reasons:

  • Low grade transformers don't regulate power very well, thus shortening the life of your bulbs.

  • Their life expectancy is only a few years, if that.

  • They tend to be hotter and louder, even loud enough to hear a humming sound on the surface it's mounted on.

  • We've also heard of meltdowns, which increase the risk of a fire.

Simply put, professional grade lighting should operate on a professional grade transformer. DecksDirect offers a wide variety of professional grade transformers to fit large or small lighting configurations.

Transformer Types


AC vs. DC Transformers

AC transformers are used most often with Incandescent fixtures. However, some LEDs are rated for both AC and DC power so don't forget to check the item description to verify the power type. Many AC transformers have built-in features such as photo eyes and/or timers.

View our AC transformer comparison chart

DC transformers are used with most LED fixtures, but some higher-end styles are rated for both AC and DC power. Check the item description on your bulbs to verify the power type required. Since most LED lights draw a small amount of power (around 1-3 watts per fixture) DC transformers tend to come in smaller wattages than AC transformers and tend to be smaller in physical size than AC transformers. Unlike AC transformers, most DC transformers are dimmable with a dimmer accessory (purchased separately).

View our DC transformer comparison chart

AC power vs. DC power can be quite confusing! Click here for additional information.

If you are unsure what type of transformer you need, let the experts at help. Give us a call at 1-888-824-5316

Single vs. Multi-tap Transformers

Single or simple-tap transformers have just one terminal which delivers current reduced to a pre-set amount, usually to 10% of the incoming voltage. Single-tap transformers are available for both AC and DC systems.

Multi-tap transformers have several terminals available (usually from 11-15 volts). This flexible voltage system ensures better current stability that prevents dimming and early bulb burnout. Multi-tap transformers are usually used for large jobs, such as landscape projects, where distance is great and/or many fixtures are being used. Since voltage drop is more prevalent with incandescent lighting systems, multi-tap transformers are only available for incandescent AC systems.

Still have questions about transformers? For additional assistance or advice, just call the experts at 1-888-824-5316.

Standard Cost

Choosing Transformer Size


Transformer calculation

Calculating Transformer Size

To determine the size of transformer needed, add up the total number of watts for each light fixture in your deck plan. Then, add another 10% for cables and connections that add hidden watts to your system. A simple equation to use is: 
Total light watts x 1.1 = transformer size needed.

Choose the transformer that most closely matches your total lamp wattage, and round the number up rather than down. You may also want to leave some room to add more lights in the future. For example, 13 fixtures all rated at 20 watts will require a 300 watt transformer (13 x 20 = 260. 260 x 1.1 = 286). To reduce stress on the bulbs and prevent early burn-out, it is a good idea to have 50% of the total transformer capacity used whenever possible.

If you are unsure what size transformer to use, ask one of the experts at by calling 1-888-824-5316.

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