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Is LED The Most Efficient Lighting Technology?
Tuesday, 30 August 2011 12:17

LED_Illustration

As we so often like to say, it depends. There are situations where LED can be the most efficient lighting technology, but there are other situations where fluorescent lighting, or other lighting technologies can still offer better real-world efficiency than LED.

That "real-world" is an important distinction.

The Real World vs. The Lab

In May of this year, a leading LED-chip manufacturer announced that they had achieved an efficiency of 231 lumens per watt in an LED chip in their lab. An efficiency of 231 lumens per watt is amazing. The only problem is that it's a long way from the lab to the real world.

That's because, in part, an LED based fixture requires quite a bit more than just an LED chip to produce light. It requires a circuit board where the LED chip is mounted, a driver that converts power coming from the wall into a form that the chip and circuit board can use, optics that direct the light to the right place and a housing that dissipates the heat generated by the fixture.

Each of those components has its own level of efficiency, and they all have to work together to turn electricity into light.

So, that's why technicians in the lab can honestly claim to have created an LED chip with an efficiency of over 200 lumens per watt, but the same company that developed that chip doesn't sell an entire LED lighting fixture with a claimed efficiency of over 75 lumens per watt.

And of course, in the real world, there's more to consider in terms of efficiency than just how well a fixture can turn electricity into lumens. You've got to think about things like the quality of the light, light distribution and how well the fixture works in a specific environment.

So to answer the question, "Is LED the most efficient lighting technology" — our best option is to compare real-world options in real-world situations.


Comparison #1 - Replacing a 60W Incandescent At Home

Even if you're not in the lighting industry, chances are good that you've swapped out an incandescent bulb at home for an energy efficient replacement.

There's been a lot of buzz lately about both compact fluorescent and LED lighting in homes. In fact, a recent survey found that 74% of US households have at least one energy efficient light source in them.

Of course, home lighting isn’t something we sell at [P2], but for most people outside of the energy efficient lighting industry, it’s a more familiar place to start our comparison of lighting efficiency.

For this comparison, we'll pick two roughly equivalent CFL & LED lamps that you could screw into a light-socket at home to see which is the most efficient.

BULB_Illustration

Representing LED, we've got the Philips AmbientLED 12.5W A19 Indoor Bulb - the close cousin of a bulb that Philips just won the L-Prize with. The difference being that while the L-Prize winning bulb is supposed to be available sometime next year, the AmbientLED A19 is available today.

Representing CFL, we've got the GE Energy Smart 13 Watt bulb, a fairly common bulb that you could pick up in most any department or hardware store this afternoon.

Here's how they stack up:

 

LED

CFL

Watts

12.5

13

Delivered Lumens

800

825

Lumens Per Watt

64

63.5

Bulb Cost

$45

$0.86

Expected Lifespan

25,000 hours

8,000 hours


So, does this answer our question? Kind of.

On paper, the efficiency of these two bulbs is nearly identical, within 0.5 lumens per watt.

There are, however, some real-world considerations that could tip the balance in favor of either fixture.

If your primary concern is price, in most situations, the CFL would be a better choice. It'll consume essentially the same amount of electricity, and even though it has a shorter lifespan, even if you replaced the CFL three times to achieve an equivalent lifespan to the LED, you'd still have only spent $2.58 in comparison to the LED's $45 initial purchase price.

However, if the fixture you're mounting the bulb in is in a place where it's a hassle to change, that $40 difference might be worth not having to deal with it for the expected 20+ years of normal usage you'll get out of the single LED.

Efficiency Winner: It Depends
Price Winner: It Depends
ROI Winner: It Depends

Comparison #2 - Replacing a 250W Metal Halide High-Bay Fixture

Now that we've covered home usage, let's move on to a comparison of the efficiency of high-bay fixtures.

Suppose you were replacing a 250W Metal Halide High-Bay fixture in a parking garage. What would be more efficient, an LED or fluorescent replacement?

Since this is the exact type of thing we make fixtures for, we'll use two [P2] fixtures in this example.

Fixture_Illustration

Representing fluorescent lighting technology, we have our SIH standard industrial hood. It's available in a variety of configurations, but with four T8 lamps in it, it will produce 10,465 lumens of light - about the same as a 250W Metal Halide fixture.

Representing the latest in LED lighting technology, we have our brand new QPD parking-garage fixture. Configured with 60 LED chips, it'll produce about the same amount of lumens as the SIH or a 250W Metal Halide fixture.

So, how do they stack up?

 

QPD LED

Fluorescent

Watts

144

107

Lumens

11,378

10,465

Lumens Per Watt

79

90

Fixture Cost*

~$600

~$100

Expected Lifespan

50,000 hours

30,000 hours

*Because of the highly customizable nature of [P2] fixtures, each order receives custom pricing, based on that order’s specifications. These are only sample end-user prices based on commonly requested configurations.

What you see in this table will surprise a lot of people. Fluorescent - a technology that's been around for 30+ years is still more efficient than LED? Well, the truth is, it depends.

The first thing to note is that while fluorescent lighting technology has been around for a long time, today's fluorescent lighting has about as much in common with the fluorescents of 30 years ago as a Model-T does with a 2012 Ford Mustang. Which is to say, not much.

While LED lighting technology has rocketed to the forefront over the past few years, fluorescent lighting technology has been steadily improving in terms of efficiency, aesthetics and longevity for the past 30 years.

So, in this case, much like our home-lighting comparison, LED and Fluorescent lighting each have characteristics that give them advantages in specific situations.

For example, in our sample scenario of replacing fixtures in a parking garage, there might be ways to make the QPD LEDs the more efficient choice, even though each fixture will have a lower lumen per watt ratio.

One of the key advantages of LED lighting is its ability to distribute light evenly over a wide area. In fact, it's much better at this than any other lighting technology.

That means that if you needed a specific minimum light level over an entire parking structure, you'd be able to achieve that level with fewer LED fixtures than you could using fluorescent or another lighting technology.

Another area where LED lighting technology really shines is in cold temperatures, for example, illuminating freezer storage areas. In sub-zero temperatures, fluorescent fixtures take a few minutes to warm up to full brightness. This means that you have to more or less turn the light on at the beginning of the work day, and leave it on until everyone goes home.

However, since LEDs come up to full brightness instantly in sub-zero temperatures, they can be fitted with occupancy sensors that only turn the light on when people are in the room. They can therefore cut their energy consumption significantly by automatically turning off when no one's around.

But of course, these are just a couple examples of factors that can affect the efficiency of any given lighting technology. The truth is, there are a whole host of other factors that could tip the scales in favor of one technology or another.

In some situations, the features of the LED-based fixtures might add enough efficiency to a system to overcome the disadvantage created by their initial cost. In other situations, fluorescent fixtures will still be the more affordable, more efficient choice.

Which brings us to our rather unsatisfying conclusion:

Efficiency Winner: It Depends
Price Winner: It Depends
ROI Winner: It Depends

So What?

All these numbers illustrate is that if you’re picking a lighting technology, and trying to make it fit with your lighting needs, you’re doing it wrong. The best way to approach any energy-efficient lighting project is to clearly define the goals of the project, and pick the technology — or mix of technologies — that meets those goals.

And if you ever need any help doing that, give our Service Hub a call. They’d be happy to help: (714) 386-5550

 

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