Choosing the Right LED Wattage: Focus on Lumens, Not Watts
When it comes to updating lighting systems with LED fixtures, a common question arises: “How many watts should I use to replace my current lights?” While understandable, this way of thinking is outdated. In the realm of LED lighting, watts only measure the power consumption of a fixture. What really matters is lumens, which represent the actual amount of light produced.
LED technology varies significantly in its ability to transform watts into lumens. This efficiency is referred to as lumens per watt (lm/W), and not all LED products are created equal in this regard. By understanding this principle, you’ll be better equipped to select the right LED product for your needs.
Replacing Metal Halide Fixtures With LEDs: A Practical Example
Let’s explore replacing a 250-watt metal halide low bay fixture in a warehouse environment. For such replacements, efficiency and light output play a pivotal role.
Our high bay LED fixtures typically operate between 130 and 160 lumens per watt. So for every watt consumed, these fixtures produce an impressive amount of light.
For example:
How to Calculate Lumens per Watt
The formula is:
Lumens per Watt = Total Lumens ÷ Fixture Wattage
Example:
- Fixture lumen output: 18,000 lumens
- Fixture power: 120 watts
- 18,000 ÷ 120 = 150 lm/W
The fixture therefore has an efficacy of 150 lumens per watt.
Correct Comparison Example
| Fixture | Power | Efficacy | Output |
|---|---|---|---|
| LED Fixture A | 120W | 150 lm/W | 18,000 lumens |
| LED Fixture B | 120W | 120 lm/W | 14,400 lumens |
| LED Fixture B at equal output | 150W | 120 lm/W | 18,000 lumens |
However, lumens per watt should not be used alone. Beam angle, optical losses, mounting height, lux, uniformity, driver reliability and thermal performance also affect the final project result.
To achieve 18,000 lumens (comparable to our product), the competitor’s fixture would require 125 watts, consuming more energy for the same light output. This illustrates why watts are not the best metric—lumens and energy efficiency are the key factors for any lighting upgrade.
Watts alone are an inadequate metric for deciding how to replace an existing light source. For instance, if a customer contacted two companies asking, “How many watts do I need to replace a 250-Watt Metal Halide?” our answer would be 100 watts, while our competitor might suggest 125 watts. To avoid confusion, we always guide customers to focus on lumens instead of watts when determining the right replacement.
That said, there’s an even bigger issue to address—efficiency. In the example above, our Low Bay Lights produce the same amount of light as the competitor’s option but consume 25 fewer watts per unit. This difference is crucial because those 25 fewer watts directly lower electricity consumption and costs. Choosing a more efficient light source means your electricity bill will noticeably decrease, simply by opting for a 100-Watt Low Bay Light over a 125-Watt version.
Related LED Selection Resources: Read Why You Should Not Buy LED Lights by Wattage, Watts, Lumens and Foot-Candles, and compare UFO LED High Bay Lights.
Efficiency is a key factor to consider when evaluating LED products in today’s market. The specifications matter; understanding lumens helps you make informed decisions. The bottom line is that lower energy consumption leads to lower expenses, and more efficient models deliver better lighting performance with less power compared to less efficient options.
Lumens Guidelines
Indoor Fixtures
250 Watts HID: 10,000 – 14,000 LED Lumens
400 Watts HID: 15,000 – 30,000 LED Lumens
1000 Watts HID: 40,000+ LED Lumens
Outdoor Fixtures
250 Watts HID: 7,000 – 15,000 LED Lumens
400 Watts HID: 15,000 – 30,000 LED Lumens
1000 Watts HID: 40,000+ LED Lumens
Pay special attention to the lumens per watt of the LED fixture or retrofit.
An LED fixture with a performance of 150 lumens per watt uses significantly less energy than one producing 100 lumens per watt.
It’s important to note that not all LEDs are created equal. Always focus on the lumens you require rather than just considering the wattage. To determine lumens per watt, divide the total lumens produced by the total watts consumed by the product. Rebates are available for both new fixtures and retrofit kits, provided they meet DLC qualifications. Ensuring a product is DLC-qualified is crucial for qualifying for rebate programs offered by utility companies.
You can verify if a product meets DLC requirements on the DesignLights Consortium website. Typically, DLC Premium classifications earn higher rebates compared to DLC Standard classifications. The actual rebate amounts are provided by your local utility company, so consult their website for specific details. All DLC products come with a minimum warranty of 5 years, and every LED fixture or retrofit kit we offer is either UL-listed or ETL-listed.
Upgrading an existing fixture with a retrofit unit does not invalidate its UL or ETL listing. Both UL and ETL certifications ensure the same rigorous testing standards and guarantee quality, with the distinction being the organization conducting the tests rather than any difference in assessment procedures.
Need Help Comparing LED Fixture Efficiency?
Send REITA the wattage, lumen output, beam angle, mounting height and application. We can help compare efficacy together with useful lux performance.Contact REITA