What Size LEDs Are Using in 100 String Lights Revealed

Most 100-string LED lights use 3mm or 5mm LED bulbs, with 5mm being the most common for their ideal balance of brightness, energy efficiency, and durability. These sizes ensure optimal spacing and consistent illumination, making them perfect for indoor and outdoor decorative lighting. Whether for holidays or year-round ambiance, the bulb size directly impacts performance and visual appeal.

Key Takeaways

• Most 100-string lights use 3mm LEDs: Ideal for bright, diffused lighting.
• 5mm LEDs offer durability: Better for outdoor or heavy-duty use.
• Mini LEDs (2mm) save space: Perfect for delicate or compact designs.
• Check wattage and voltage: Ensures compatibility with your power source.
• Size impacts brightness: Larger LEDs often provide higher lumens.
• Consider spacing between bulbs: Closer spacing enhances even light distribution.

Understanding the Basics of LED String Lights

What Are LED String Lights?

LED string lights have become a staple in both home decor and event lighting, offering a blend of energy efficiency, durability, and aesthetic appeal. Unlike traditional incandescent bulbs, LEDs (Light Emitting Diodes) use semiconductor technology to convert electricity into light, resulting in minimal heat and significantly longer lifespans—often exceeding 25,000 to 50,000 hours. These qualities make them ideal for indoor and outdoor applications, from holiday displays to permanent garden installations.

The “100 string lights” configuration refers to a strand containing 100 individual LED bulbs, typically spaced at regular intervals (e.g., 4 inches apart). This density strikes a balance between brightness and coverage, making it a popular choice for wrapping trees, outlining windows, or draping across ceilings. But what truly defines the look and performance of these lights? The answer lies in the size of the LEDs used.

Why LED Size Matters

LED size isn’t just about physical dimensions—it directly impacts brightness, color temperature, energy consumption, and beam angle. For example, smaller LEDs (like 3mm) produce a more diffused glow, ideal for soft ambiance, while larger LEDs (like 5mm or 10mm) deliver focused, brighter light perfect for task or accent lighting. Understanding these differences helps you choose the right string lights for your needs.

Moreover, LED size influences heat dissipation and circuitry design. Larger LEDs often require better heat management, which can affect the strand’s longevity. Meanwhile, smaller LEDs allow for tighter spacing and more compact designs. In this guide, we’ll dive deep into the most common LED sizes used in 100-string light sets, their pros and cons, and how to pick the best option for your space.

Common LED Sizes in 100 String Lights

The 3mm LED: Tiny but Mighty

The 3mm LED is the smallest standard size found in many 100-string light sets. Measuring just 3 millimeters in diameter, these LEDs are often called “mini LEDs” due to their compact form. Despite their size, they pack a punch in terms of versatility and energy efficiency.

• Brightness: Lower lumen output (around 100–200 mcd), creating a subtle, twinkling effect.
• Beam Angle: Typically 120°–140°, offering wide, even light distribution.
• Energy Use: Ultra-low power draw (~0.05–0.1 watts per LED), making them ideal for battery-powered or solar-operated strands.

Best Use Cases: 3mm LEDs excel in applications requiring a soft, ambient glow—think wedding backdrops, fairy light canopies, or delicate Christmas tree decorations. Their small size allows for high bulb density (e.g., 4-inch spacing), creating a “starry sky” effect. Brands like GE and Philips often use 3mm LEDs in their premium indoor string lights.

Pro Tip: Pair 3mm LEDs with frosted or faceted lenses to enhance diffusion. Avoid using them for task lighting, as their brightness may be insufficient for reading or detailed work.

The 5mm LED: The Industry Standard

The 5mm LED is the most widely used size in 100-string lights, striking a balance between brightness, size, and cost. At 5 millimeters in diameter, these LEDs are slightly larger than 3mm versions, offering improved visibility without sacrificing elegance.

• Brightness: 500–1,000 mcd (millicandela), significantly brighter than 3mm LEDs.
• Beam Angle: 110°–130°, with a slightly more focused beam than 3mm models.
• Energy Use: ~0.1–0.2 watts per LED, still highly efficient.

Best Use Cases: 5mm LEDs are the go-to choice for general-purpose lighting. They work well for:

• Outdoor holiday displays (e.g., rooflines, fences)
• Indoor accent lighting (e.g., bookshelves, headboards)
• Event decor (e.g., marquee letters, table centerpieces)

Real-World Example: The Twinkly Smart LED String Lights use 5mm LEDs with RGB color options, allowing users to customize patterns via an app. Their brightness is perfect for both festive and everyday use.

Pro Tip: Opt for 5mm LEDs with clear or transparent lenses for maximum brightness. Use colored lenses (e.g., red, blue) for themed decor, but note that they may reduce overall light output.

The 10mm LED: Bold and Bright

The 10mm LED is the largest common size in 100-string lights, offering high visibility and dramatic impact. These LEDs are often used in commercial-grade lighting due to their superior brightness and durability.

• Brightness: 1,500–3,000 mcd, ideal for outdoor or high-visibility areas.
• Beam Angle: 60°–90°, creating a more focused, spotlight-like effect.
• Energy Use: ~0.2–0.3 watts per LED, still efficient but slightly higher than smaller sizes.

Best Use Cases: 10mm LEDs are perfect for:

• Large outdoor spaces (e.g., patios, gardens, commercial storefronts)
• High-ceiling installations (e.g., warehouses, event venues)
• Areas requiring long-range visibility (e.g., parking lots, signage)

Real-World Example: The Feit Electric 100-Light LED String Set uses 10mm LEDs with a 10-foot spacing between bulbs, designed for expansive outdoor displays. Their bright, focused beam cuts through darkness, making them ideal for holiday light shows.

Pro Tip: Use 10mm LEDs with adjustable sockets (e.g., E26/E27 bases) for easy replacement. Avoid using them in small rooms, as their brightness can be overwhelming.

Less Common LED Sizes and Specialty Options

The 2mm and 8mm LEDs: Niche Choices

While 3mm, 5mm, and 10mm dominate the market, some manufacturers use 2mm or 8mm LEDs for specific applications.

• 2mm LEDs: Extremely compact (2mm diameter), used in ultra-thin or flexible strips (e.g., USB-powered LED strips). Brightness: ~50–100 mcd. Ideal for tight spaces like picture frames or DIY projects.
• 8mm LEDs: A middle ground between 5mm and 10mm, offering 800–1,500 mcd brightness. Often found in vintage-style string lights with exposed bulbs.

Specialty Example: The Brightown Vintage LED String Lights use 8mm LEDs with Edison-style bulbs, combining retro aesthetics with modern efficiency. Their warm white light (2700K) mimics incandescent bulbs but uses 80% less energy.

Pro Tip: For DIY enthusiasts, 2mm LEDs allow for custom spacing (e.g., 2-inch intervals) to create unique patterns. Use 8mm LEDs when you want a “bulb-like” look without the heat of incandescents.

SMD LEDs: The Modern Alternative

SMD (Surface-Mount Device) LEDs aren’t measured in millimeters like traditional LEDs. Instead, they’re classified by package sizes (e.g., 2835, 3528, 5050). SMDs are often used in flexible LED strips but are increasingly appearing in 100-string lights for their:

• Higher Brightness: 5050 SMDs can output 30–50 lumens per LED.
• Color Options: RGB, tunable white, and UV variants.
• Durability: No glass bulbs—resistant to vibration and impact.

Real-World Example: The Nanoleaf Shapes line uses SMD LEDs in modular panels, but similar technology is found in smart string lights like LIFX String, which offers voice-controlled color changes and scheduling.

Pro Tip: SMD LEDs require a diffuser (e.g., silicone tube) to soften their intense light. They’re best for modern, tech-forward decor.

How LED Size Affects Performance and Aesthetics

Brightness and Light Spread

The size of an LED determines its lumen output and beam angle, which together define how light is distributed. Here’s a comparison:

LED Size	Avg. Brightness (mcd)	Beam Angle	Light Spread
2mm	50–100	140°	Wide, diffused
3mm	100–200	120°–140°	Soft, ambient
5mm	500–1,000	110°–130°	Balanced
8mm	800–1,500	100°–120°	Focused, slightly diffuse
10mm	1,500–3,000	60°–90°	Narrow, spotlight-like
SMD 5050	3,000–5,000	120°–160°	Intense, wide

Key Takeaway: Smaller LEDs create a softer, more uniform glow, while larger LEDs offer higher intensity and directional light. For example, 10mm LEDs are better for outlining architectural features, whereas 3mm LEDs excel at creating a “twinkling” effect on trees.

Energy Efficiency and Heat Management

LED size also impacts energy consumption and heat generation:

• Smaller LEDs (2mm–5mm): Lower power draw (0.05–0.2W/LED), minimal heat. Ideal for long-term use (e.g., permanent installations).
• Larger LEDs (8mm–10mm): Higher power draw (0.2–0.3W/LED), more heat. Often include heat sinks or thermal pads in the design.
• SMD LEDs: Varies by package. 5050 SMDs generate more heat but are designed with built-in thermal management.

Pro Tip: For battery-powered 100-string lights, choose 3mm or 5mm LEDs to maximize battery life. For outdoor use, ensure larger LEDs have weatherproof housing to prevent heat-related damage.

Aesthetic Impact

LED size influences the visual weight of the strand:

• 3mm/2mm: Delicate, “floating” look. Best for minimalist or vintage decor.
• 5mm: Classic, versatile appearance. Fits most modern and traditional styles.
• 10mm/8mm: Bold, statement-making. Ideal for industrial or rustic themes.
• SMD: Sleek, futuristic. Perfect for smart homes or tech-centric spaces.

Real-World Example: A 100-string light set with 5mm LEDs wrapped around a tree creates a balanced, festive look. The same strand with 10mm LEDs would appear more dramatic, with individual bulbs standing out sharply.

Choosing the Right LED Size for Your Needs

Indoor vs. Outdoor Use

Your environment dictates the best LED size:

• Indoor: Prioritize ambiance. Choose 3mm or 5mm LEDs for bedrooms, living rooms, or dining areas. SMD LEDs work well for accent lighting (e.g., under cabinets).
• Outdoor: Focus on visibility and durability. Opt for 5mm, 8mm, or 10mm LEDs with weatherproof ratings (IP65+). SMD LEDs with silicone covers are ideal for rainy climates.

Pro Tip: For indoor-outdoor versatility, select 5mm LEDs with clear, shatterproof lenses. They offer a good balance of brightness and subtlety.

Brightness and Spacing Considerations

Bulb spacing (distance between LEDs) interacts with size:

• 4–6 inch spacing: Works best with 3mm or 5mm LEDs. Creates a “dense” look.
• 8–12 inch spacing: Pairs with 8mm or 10mm LEDs. Emphasizes individual bulbs.
• 12+ inch spacing: Requires 10mm or SMD LEDs for adequate brightness.

Example: A 100-string light set with 4-inch spacing and 5mm LEDs covers ~33 feet of space with a cohesive glow. The same set with 10-inch spacing and 10mm LEDs covers ~83 feet but appears more “spotty.”

Color Temperature and Lens Options

LED size doesn’t affect color temperature (measured in Kelvin), but it influences how color is perceived:

• 2700K–3000K (Warm White): Best with 3mm/5mm LEDs for cozy ambiance.
• 4000K–5000K (Cool White): Pairs with 8mm/10mm LEDs for a crisp, modern look.
• RGB (Color-Changing): SMD LEDs offer the widest color range.

Pro Tip: Use frosted lenses with warm white LEDs to soften the light. For cool white, clear lenses enhance brightness.

Maintenance and Longevity of LED String Lights

Lifespan by LED Size

All LEDs last longer than incandescent bulbs, but size affects longevity:

• 2mm–5mm LEDs: 30,000–50,000 hours (3–5 years of continuous use).
• 8mm–10mm LEDs: 25,000–40,000 hours (due to higher heat output).
• SMD LEDs: 30,000–50,000 hours (with proper heat management).

Pro Tip: Avoid overloading circuits—connect no more than 3–4 100-string sets in series. Use timers to extend lifespan.

Replacing Faulty LEDs

Most 100-string lights have non-replaceable LEDs (soldered to the circuit). However:

• 3mm/5mm LEDs: Often use socketed designs (e.g., mini candelabra bases). Replaceable with basic tools.
• 10mm LEDs: Some models have E26/E27 sockets for easy swaps.
• SMD LEDs: Require soldering—best left to professionals.

Example: The Brightown Replaceable LED String Lights use 5mm LEDs with removable sockets, making repairs simple.

Pro Tip: Keep spare LEDs and a soldering kit for DIY fixes. For non-replaceable strands, contact the manufacturer for warranty service.

Conclusion: Making an Informed Choice

Choosing the right LED size for your 100-string lights isn’t just about aesthetics—it’s about matching performance to your space, needs, and environment. From the delicate glow of 3mm LEDs to the bold brilliance of 10mm and SMD options, each size offers unique advantages. Whether you’re lighting a cozy bedroom, a sprawling garden, or a high-tech smart home, understanding LED sizes empowers you to create the perfect ambiance.

Final Recommendations:

• For soft, ambient lighting, choose 3mm or 5mm LEDs.
• For high visibility and outdoor use, opt for 8mm or 10mm LEDs.
• For color-changing or smart features, select SMD LEDs.
• Always check bulb spacing, color temperature, and weatherproof ratings.

By prioritizing quality, efficiency, and design, your 100-string lights will shine brightly for years to come. Remember: the right LED size isn’t just about the light—it’s about the experience it creates.

Frequently Asked Questions

What size LEDs are typically used in 100 string lights?

Most 100-string LED lights use **5mm or 3mm LED bulbs**, as these sizes balance brightness, energy efficiency, and compact spacing. Smaller 3mm LEDs are common for delicate, twinkling effects, while 5mm LEDs offer brighter, more focused illumination.

Are the LED sizes different for indoor vs. outdoor 100-string lights?

Generally, the LED size (like 3mm or 5mm) remains consistent, but outdoor 100-string lights often use **weatherproof coatings or shatterproof casings** for durability. The core LED size for 100-string lights rarely changes based on location.

Do 100-string LED lights use the same size LEDs as traditional incandescent string lights?

No, traditional incandescent string lights usually have larger **E12 or E17 bulb bases**, while 100-string LED lights use tiny 3mm/5mm LEDs for energy efficiency and lower heat output. The LED size in 100-string lights is much smaller and more compact.

How does LED size affect brightness in 100-string lights?

Larger 5mm LEDs in 100-string lights produce brighter, more concentrated light, while 3mm LEDs create a softer, diffused glow. The LED size directly impacts the ambiance and visibility of your string lights.

Can I replace the LEDs in my 100-string lights with a different size?

Replacing LEDs in 100-string lights is tricky due to soldered connections and tight spacing. Stick to the original **3mm or 5mm LED size** to avoid damaging the circuit or altering the light’s performance.

What’s the most energy-efficient LED size for 100-string lights?

**3mm LEDs** are often more energy-efficient in 100-string lights due to their lower power draw, making them ideal for long-term use. However, 5mm LEDs can still be efficient if paired with high-quality drivers and dimming features.