100W vs. 150W UFO: Sizing the Right Light for a 2-Car Garage

When upgrading a standard 2-car garage (typically 20'x20'), the choice between a 100W and a 150W high-output LED fixture often feels like a simple matter of "more is better." However, in a residential workshop or automotive bay, raw power frequently takes a backseat to light distribution and visual comfort. Selecting the wrong wattage or layout can transform a productive workspace into a cave of harsh glares and deep shadows.

For a ceiling height of 8 to 12 feet, the decision hinge points are not just about total lumens, but about how those lumens interact with your workbenches and vehicle bays. We have found that while a single high-wattage fixture seems cost-effective, a distributed multi-light system almost always provides a superior technical and ergonomic outcome.

The Lumen vs. Wattage Paradigm

In the legacy era of Metal Halide (MH) and High-Pressure Sodium (HPS) lighting, wattage was the primary indicator of brightness. With modern Solid-State Lighting (SSL), the focus has shifted to luminous efficacy—measured in lumens per watt (lm/W). According to the IES LM-79-19 Standard, which defines the approved method for optical and electrical measurements of LED products, a fixture's "performance report card" is based on its total delivered lumens rather than the power it consumes.

A high-quality 100W circular industrial fixture typically produces between 13,000 and 15,000 lumens, while a 150W variant delivers approximately 18,000 to 22,000 lumens. In a 400-square-foot garage, a single 150W light creates a massive "hot spot" directly underneath the fixture, reaching 80+ foot-candles (fc), while the corners of the garage may drop below 10 fc. This creates extreme contrast, which forces the eye to constantly readjust—a primary cause of ocular fatigue during detailed tasks like fabrication or engine repair.

Comparison of 100W vs. 150W Performance

The 2-Car Garage Layout: Managing Shadows and Uniformity

For a 2-car garage, the goal is "Uniformity of Illumination." The ANSI/IES RP-7-21 Recommended Practice for Lighting Industrial Facilities emphasizes that the ratio between maximum and minimum light levels should be kept low to ensure safety and productivity.

In a 20'x20' space with a 9-foot ceiling, a single 150W fixture mounted in the center is a common mistake. Because the light source is concentrated, the hood of a car or a person standing at a workbench will cast long, dark shadows exactly where light is needed most.

By contrast, using two 100W fixtures spaced 10 feet apart (centered over each parking bay) provides overlapping light beams. This "cross-lighting" fills in the shadows created by the user's body or large equipment. While the 150W fixture is technically "bright," the dual 100W setup is "functional."

Experiment Insights: 2x100W vs. 1x150W Economics

We conducted a simulation comparing a "distributed" 100W system against a "centralized" 150W system for a DIY homeowner performing 2,000 hours of work annually at an electricity rate of $0.14/kWh.

The "Glass Box" ROI Analysis

The results revealed that while the 150W fixture has a lower upfront purchase price, the 2x100W configuration is the superior long-term investment due to utility incentives and performance gains.

• Annual Energy Savings: Replacing an old 400W metal halide with two 100W LEDs saves approximately 1,432 kWh per year, translating to $220.75 in annual savings.
• Payback Period: Despite the higher initial cost of two fixtures, the faster energy reduction and eligibility for higher total rebates result in a payback period of just 1.09 years.
• Rebate Potential: Most utility companies offer rebates based on the DesignLights Consortium (DLC) Qualified Products List. Because two fixtures represent two "rebateable" units, the total cash back can often cover 50-70% of the total project cost.

Technical Compliance: Beyond the Brightness

When selecting your fixture, the "Expertise" lies in the certifications. A "bright" light that is not safe is a liability.

1. Safety Certifications (UL/ETL)

Ensure the fixture is UL 1598 listed. This standard covers luminaires for use in non-hazardous locations and ensures the housing can handle the thermal load of the LEDs without becoming a fire hazard. For garages where moisture or dust is present (e.g., detailing bays), an IP65 rating (Ingress Protection) is mandatory to prevent internal component failure.

2. Dimming Compatibility

A common "gotcha" for DIYers is the dimming system. High-output industrial lights typically use 0-10V dimming. This requires two low-voltage wires (usually purple and gray) to be run to a compatible 0-10V dimmer switch. Attempting to use a standard residential "triac" dimmer designed for incandescent bulbs will cause the LED driver to hum, flicker, or fail prematurely. If you do not plan to dim the lights, these wires can simply be capped off.

3. Color Temperature (CCT) and CRI

For a garage, we recommend a Correlated Color Temperature (CCT) of 5000K (Daylight White). This promotes alertness and provides the best contrast for seeing fine details. Furthermore, look for a Color Rendering Index (CRI) of 80 or higher. A high CRI ensures that wire colors (red vs. orange) and paint finishes are represented accurately—critical for automotive work.

Installation Best Practices and Safety Pitfalls

Installing these fixtures is a straightforward DIY task, but professional-grade results require attention to mechanical and electrical details.

The Safety Cable Requirement

High-output industrial fixtures are heavy. While the primary mounting method is usually a heavy-duty hook or bracket, you must secure the included safety cable independently. Do not loop the safety cable through the same hook as the fixture; instead, anchor it to a separate joist or structural member. This prevents the fixture from falling if the primary hook fails or if the light is accidentally struck by a ladder or piece of lumber.

Wiring and the NEC

All wiring should comply with the National Electrical Code (NEC). In a garage, if you are plugging the fixtures into an outlet, ensure the circuit is GFCI (Ground Fault Circuit Interrupter) protected if it is in a location prone to dampness. Most high-bay fixtures come with a 5-foot or 6-foot power cord and a standard 3-prong plug, making them "plug-and-play" for most modern garages.

Spacing and Height

• For 8–10 ft ceilings: Space 100W fixtures 8–10 feet apart.
• For 12–15 ft ceilings: 150W fixtures become more viable, but should still be spaced 12 feet apart to ensure overlapping light cones.
• The "Wall Gap": Always mount fixtures at least 3–4 feet away from walls to prevent "hot spots" on the vertical surfaces and to allow light to bounce back into the center of the room.

Decision Matrix: Which One Should You Buy?

To simplify the choice, evaluate your garage based on its primary use case:

1. The "Storage & Basic Utility" Garage: If you only need to see well enough to park cars and find boxes, a single 150W fixture in the center is the most economical "one-and-done" solution.
2. The "Weekend Warrior" Workshop: If you spend time at a workbench or perform oil changes, choose two 100W fixtures. The shadow reduction will significantly improve your efficiency.
3. The "Professional Detailing" Bay: For high-end paint correction and detailing, we recommend four 100W fixtures or a combination of circular bays and linear shop lights to provide light from multiple angles, eliminating all shadows.

For more detailed guidance on planning your space, you may find our article on How Far Apart to Space UFO High Bays in a Workshop helpful in calculating exact coordinates.

YMYL Disclaimer: This article is for informational purposes only. Electrical work involves risks of fire and shock. Always consult a licensed electrician and adhere to your local building codes before performing any wiring or structural modifications.

References

• DesignLights Consortium (DLC) Qualified Products List
• IES LM-79-19: Optical and Electrical Measurements of Solid-State Lighting Products
• ANSI/IES RP-7-21: Recommended Practice for Lighting Industrial Facilities
• UL 1598 Standard for Luminaires
• National Electrical Code (NEC) Overview
• DSIRE: Database of State Incentives for Renewables & Efficiency