Lumens to Watts Conversion - Never Buy Based on Watts

This is a common message we try to impart to our customers when they call us. For example, it is not uncommon for us to get a call to quote a price on high bays and be told they need a price on a 150-Watt LED fixture. The most important thing we can do for our customers is to explain LED efficiency and help them select the right LED product based on performance, not just wattage.

What are Watts?

Watts measure energy consumption-the amount of electricity a fixture uses. When you pay your utility bill, you’re paying for the kilowatt-hours of energy consumed. A 400-watt metal halide shop light consumes 400 watts of energy while operating.

However, watts don’t directly represent the amount of light (lumens) produced. Over time, we’ve learned to associate light levels with specific bulb types. When someone says “I want the brightness of a 400-watt metal halide,” they’re really referring to the visible light output, which happens to come from a bulb that consumes 400 watts.

What are Lumens?

A lumen is the standard measurement of visible light output. The higher the lumen count, the brighter the light appears to the human eye. When evaluating LED fixtures, manufacturers typically provide three key specifications:

• Initial Lumens: Light output when the fixture is new
• L70 Rating: Operating hours until the fixture produces 70% of its initial lumens (industry standard for usable life)
• Rated Life: Expected operational hours before fixture failure or major maintenance is required

Understanding Lumens Per Watt (Efficacy)

Efficacy, measured in lumens per watt (lm/W), indicates how efficiently a light source converts electrical energy into visible light. This metric is crucial for comparing different lighting technologies:

Traditional metal halide fixtures typically achieve 75-90 lumens per watt. A 400-watt metal halide produces approximately 32,000 lumens (80 lm/W efficiency).

LED technology offers significantly higher efficiency, with quality fixtures achieving 130-180+ lumens per watt. Our commercial and industrial LED fixtures commonly deliver 150-165 lumens per watt, more than double the efficiency of the metal halide fixtures they replace.

Important: LED efficacy varies significantly between manufacturers and product lines. Consider these examples for producing 20,000 lumens:

• Lower-efficiency LED at 100 lm/W requires 200 watts
• Higher-efficiency LED at 150 lm/W requires only 133 watts

When comparing LED products, always evaluate efficacy alongside total lumen output and operating costs.

How to Select the Most Energy-Efficient LED Fixture

Follow this systematic approach when replacing existing lighting:

1. Measure current light levels: Take foot-candle readings throughout your space to establish baseline illumination requirements. Standard recommendations vary by application (20-50 FC for warehouses, 30-75 FC for retail spaces).
2. Calculate lumen requirements: Determine total lumens needed to maintain or improve current lighting quality. Professional lighting companies like LED Lighting Supply use photometric analysis and specialized software to model light distribution and predict performance in your specific space.
3. Compare fixture efficacy: Select the LED fixture with the highest lumens-per-watt rating that meets your lumen requirements. This determines your actual energy consumption and operating costs.

Quality Considerations: Why Efficiency Matters Long-Term

While we maintain competitive pricing, we regularly assist customers who need to replace or supplement inadequate LED installations purchased elsewhere based solely on low price.

Lower-quality LED products often feature:

• Poor efficacy (100 lm/W or less)
• Shorter L70 ratings
• Inconsistent light distribution
• Higher failure rates

These issues result in a higher total cost of ownership through increased energy consumption, more frequent replacements, and inadequate illumination.

Professional Installation Note: LED fixture installation often involves electrical work that should be performed by qualified electricians in accordance with local electrical codes and safety requirements.