How to Choose the Right Transformer Size for Your Outdoor Lighting System

Why Transformer Size Matters in Landscape Lighting

A transformer is the heart of any low-voltage outdoor lighting system. Even the highest-quality fixtures won’t perform properly if the transformer is undersized — or unnecessarily oversized.

At Kings Outdoor Lighting, we design systems where transformers are carefully matched to the lighting load to ensure consistent brightness, long fixture life, and professional results.

What Does a Landscape Lighting Transformer Do?

A low-voltage transformer converts standard household power (120V) into 12–15V, which is safe and efficient for outdoor lighting.

The transformer must:

• Supply enough power (watts) to all fixtures

• Maintain stable voltage

• Allow room for future expansion

Step 1: Calculate Your Total Wattage

Start by adding the wattage of every fixture in your system.

Example:

• 10 spotlights at 5W each = 50W

• 4 floodlights at 10W each = 40W
  Total Load = 90W

Step 2: Add a Safety Margin (Very Important)

Professionals never run transformers at 100% capacity. A good rule is to use only 70–80% of the transformer’s rated wattage.

Why?

• Prevents overheating

• Extends transformer lifespan

• Allows for future fixture additions

90W system ÷ 0.8 = 113W minimum transformer size

In this case, a 150W transformer would be the correct choice.

Step 3: Choose the Right Transformer Size

Choosing slightly larger is always better than choosing too small.

Step 4: Consider Multiple Output Taps

High-quality transformers offer multiple voltage taps (12V, 13V, 14V, 15V).

These allow you to:

• Compensate for voltage drop

• Balance brightness across long wire runs

• Fine-tune professional results

This is especially important for larger landscapes.

Step 5: Plan for Expansion

Most homeowners add lights over time. Choosing a transformer with extra capacity saves money and labor later.

Ask yourself:

• Will I add more lights next year?

• Do I plan to expand to the backyard?

If yes, size up now.

Common Transformer Mistakes

• Undersizing the transformer

• Running at 100% capacity

• Ignoring voltage drop

• Using indoor-rated transformers outdoors

Final Thoughts

Choosing the right transformer ensures your outdoor lighting system performs reliably for years. Proper sizing protects your investment and delivers consistent, professional-grade illumination.

👑 Explore premium low-voltage transformers at KingsOutdoorLighting.com and power your lighting system the right way.