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Your LED Lighting Guide: Lumens, Watts and Efficacy Explained

Monday, March 12, 2018 By Kate Reynolds


Upgrading to LED Lighting Technology: What You Need to Look For

Whether you are new to the lighting retrofit business or a seasoned expert, picking the right LED fixture, lamp or kit for your space can be challenging. So, how do you choose?

In this blog, we’ll discuss current and projected benchmarks for the efficacy of LED packages and complete luminaires, as well as provide comparisons to conventional technologies.

There’s a lot of technical information below, and we hope you find it helpful. Furthermore, if you have other questions regarding the facets of LED technology, please feel free to contact us anytime.

Why Lumens Are Important

In 2011, the US Federal Trade Commission made it a requirement to measure LED lights by Lumens because they deemed it more important to dictate how bright the bulb was, rather than power output. Even though this runs counter to our cultural understanding of a ’60 Watt Bulb’, it’s a good change. The importance of Lumens as a unit of measurement in LED lights allows us all to have earnest comparisons when specifying LED Lighting.

The difference between Watts and Lumens:

  • A watt is the standard unit of power, the expended energy – the input to a luminaire.
  • A lumen is the standard unit of light emitted by a device, the luminous flux – the output from a luminaire.

With this information in mind, it’s important to note that in today’s landscape of LED Lighting, LED driver chips and the LEDs themselves vary greatly in how efficiently they convert electricity (watts) to light (lumens). This is because of differences in light quality, product lifetime, color, and dimmability.

Lamp and Luminaire Efficacy

One of the best known advantages is energy efficiency – which can translate into considerable cost savings over time. However, as mentioned above, when it comes to LED Lighting, there are various factors to take into account when calculating that metric. This is because the energy efficiency of any lighting system depends on more than just the efficiency of the light source itself.

In the case of LED lighting and technology, these extra factors include:

  • Color Quality
  • Lifetime
  • Color Stability
  • Light Output and Distribution
  • Dimmability

In addition to these considerations, LED products are also made up of a combination of technical components – each with their own efficacy. This nuanced industry knowledge must be leveraged when looking at each of the following as well:

  • Individual Chips
  • LED Luminaire
  • LED Driver
  • Thermal and Optical Losses

Pro Tips: How to Avoid the Loss Mechanisms of LED Luminaires

Thermal effects, driver losses, and optical inefficiencies all combine to reduce the efficacy of LED luminaires. When considered collectively, these loss mechanisms can result in a decrease in efficacy of greater than 30%. Here’s what to watch out for:

Thermal Effects–
A major factor in determining the lumen output of an LED is junction temperature. As temperature rises, the light-generation process becomes less efficient and fewer lumens are emitted. For this reason, LED luminaires generally require a thermal management system. However, even in a well-designed product, the junction temperature may rise significantly above laboratory conditions, which could result in up to a 15% decrease in efficacy. It’s vital to always understand the conditions of the space in choosing the right LED luminaire.

Driver Losses –
Fluorescent and HID light sources cannot function without a ballast, which provides a starting voltage and limits electrical current to the lamp. Similarly, LED’s require a driver, which is comprised of both a power source and electronic control circuitry. Most drivers convert line voltage to low voltage and current from AC to DC, and may include supplementary electronics for dimming and/or color correction. In choosing the correct driver for the system the LED manufacturer considers many variables, dimming, lumen output, voltage all important features essential to optimizing the lighting system performance.

Optical Losses –
Regardless of source type, the use of lenses, reflectors or other optical systems to shape a product’s distribution ultimately reduces the total amount of emitted light. For LED’s, this is another contributing factor in the difference between package efficacy and lamp luminaire efficacy. However, the magnitude of the effect is difficult to state given the large diversity of fixtures in the marketplace.

Directionality Matters

LED Lighting is more directional than previous lighting technologies because individual LED’s can be aimed in any direction. Because of this, the lumen output needed for LEDs to achieve the same brightness as older technology is lower.

This is where a lighting layout will help immensely. It’s the only way to make sure that you will get the correct amount of light for the area that you need to illuminate. A lighting layout will define the lumen output of your old fixtures and help to analyze new possibilities that give you the maximum amount of light. It will also help save money on your electric bill.


Conclusion: LED Technology is Rapidly Changing

The main takeaway here is that when choosing an LED fixture, it’s more complex than just wattage and lumens. Remember to look closely at the other characteristics of LED technology – taking into consideration color quality, luminous intensity, distribution/directionality and dimmability.

If you’re unsure of where to go from here, we suggest finding trusted partners who can help. By leveraging nuanced expertise to answer questions, perform photmetrics, create layouts, design with the right fixtures and right optical patterns in mind – allowing for lowest wattage and the correct lumen package for your space – you will save money and headaches in the long run.

Filed under: Illumetek, LED

About Illumetek

Illumetek is a National Program Management company facilitating installs, updates, compliance and rebates for Lighting, Electrical, and associated Controls. If you have additional questions regarding LED lighting technology or design, please feel free to contact us anytime.

Reach out to Illumetek

Illumetek is a National Program Management company facilitating installs, updates, compliance and rebates for Lighting, Electrical, and associated Controls. Contact us today!