While LED technology has been the darling of fixture designers, linear fluorescent lamp and ballast manufacturers have been continuing to develop a diverse range of products that round out a comprehensive toolbox for sustainable design. In addition to providing smooth light output, high color rendering, a variety of color temperature options, and good value pricing, linear fluorescent lamp-life has slowly been increasing, bringing it in line with the rated life claims of LED systems.

Are LEDS really the best option for a light source with an extended rated life? Rated life of white light LED systems currently hovers around 50,000 hours. Of course, that exciting number needs to have IES standard LM-79-2008 and/or LM-80-2008 testing to give it credibility – and LED life is dependent on thermal management, meaning that long life can be compromised by excessive heat being trapped at the diodes.

Meanwhile, lamp manufacturers are introducing new T5 and T8 fluorescent lamps with similarly extended lifespans. Newer T8 lamps on instant-start ballasts can last as long as LEDs, or, with program-start ballasts, even 55,000 hours.

However, one thing the LED has done for fluorescent technology is reinforce the importance of the entire lighting system, in this case bringing the combination of lamp, ballast, and controls to the forefront. In linear fluorescent fixtures, it is the total package – lamp, ballast, and system efficiency – that counts. A common myth persists that T5 and T5HO lamps are more efficient than T8 because they’re a newer format, but in reality T8 lamps win the race, consistently offering better efficacy (light output, or lumens per watt).

Standard-output 28-watt T5 lamps produce around 2,900 lumens with a connected load of 34 watts (85 lumens per watt); high-output 54-watt T5HO lamps produce 5,000 lumens for 62 watts (81 lumens per watt). In contrast, a 32-watt T8 lamp with 3100 lumens on a high-efficiency ballast (0.88 ballast factor ballast) offers 28 watts – 97 lumens per watt.

T5 and T5HO are still priced at two to three times the cost of T8 lamps. The real potential of T5 and T5HO lamps is that their smaller diameter allows better optical control, resulting in better reflector design, smaller fixture profiles using less material, and the opportunity for more efficient photometric performance.

To use T8 lamps successfully, there are lots of options to keep in mind. Four-foot T8 lamps come in many varieties: F32T8, F28T8, and F25T8 which allows for the design of tailored systems, with light levels and power densities to suit a project’s needs. But, should you need a controllable system that requires dimming, then the F32T8 in most cases is the only lamp that dimming ballasts want to work with (although ballast manufacturers are working on products to fill this gap).

Take charge and specify ballasts to write a better energy story. High-efficiency ballasts can result in higher system efficacy, using less power, but they need to be identified in fixture specifications in order to be provided. Otherwise you will end up with generic electronic ballasts (GEB) at the manufacturer’s discretion. High-efficiency, high-ballast-factor ballasts can over-drive T8 lamps to produce more light when needed, within allowable power-density criteria, without compromising rated lamp-life. This option is helpful in situations where one lamp is not quite enough light, but a project can’t allow the power density of adding a second lamp. When one lamp is too much, low-ballast-factor ballasts with high-efficacy lamps can provide a cost-effective continuous glowing cove, such as those used at the University of Chicago’s Gordon Center for Integrative Science, where a glow was desired to create a lantern-like effect.

High/low ballasts offer cost-effective switching options for meeting code requirements when the budget can’t afford a dimming system. However, care should be taken to determine if the 50% power level of this type of ballast delivers light levels appropriate for the space – otherwise the lights will always be switched to full output by the users.

Dimming ballasts save energy, and have been finding their way onto more mainstream projects (to support daylight-responsive dimming, or lower light levels during classroom projection), but the reality is that at full power, dimmable ballasts consume more energy than a standard high-efficiency ballast. There is a campaign for code criteria to recognize that power consumption over time is a more accurate way to document power and energy savings than connected load. Until that happens, dimmed fluorescent lamps use little energy, but in power-density calculations, they still exact a premium in terms of connected load.

Photo Credits: Arria Belli (tortoise), Polandeze (hare), Anton Grassl/Esto (project)

I love LEDs. Really, I do! They offer so many possibilities for new ways to light our world with less negative environmental impact. And besides, they’re cool! What I can’t stomach is the continuing hype. Frustration with LED hype is old news for lighting designers and for readers of this blog, but I thought by now it would have simmered down. It hasn’t. That LED Kool-Aid is still being poured and plenty of people are still chugging it down.

There are two flavors of this Kool-Aid that are really bugging me these days. Here they are:

Flavor #1: “Berry, Berry, Efficient”

Why are we still hearing unqualified claims about how LEDs are super-efficient? Claims like “use 80% less energy”, “seven times more efficient”, or the headline on a recent New York Times article, “LED Bulbs Save Substantial Energy, a Study Finds”. The question always should be, COMPARED TO WHAT?

So, based on manufacturers’ data, here is my grossly oversimplified analysis of how efficacious LEDs really are.

LED fixture efficacy compared to:

• Incandescent/halogen fixtures: 0 to 5 times better
• Compact fluorescent fixtures: about the same
• Linear fluorescent fixtures: 25% better to 50% worse
• Metal halide fixtures: about the same to 50% worse
• High-pressure sodium fixtures: about the same

So if I’m right, where are these claims coming from? They may start with misleading statements by manufacturers, but I think it is the popular media that is mainly to blame, for not doing the research and then promulgating bad information. This is picked up by the consumer and by public policy people, and then the more it is repeated, the more it must be true!

Here’s an example. The City of Boston is currently testing six different pedestrian-scale post-top fixtures on the Boston Common and asking for public reaction. Right on the project web site it says things like “Light Emitting Diodes (LEDs) use far less energy in producing more and better quality light than traditional lighting,” and “The large number of city street lights (67,000+) has the potential to significantly cut energy use and carbon emissions (currently 24,000 tons/yr) by switching to LED lighting,” and “High efficiency with the potential to offer 50 to 80 percent energy savings”.

Where do they get this stuff? Maybe it is the New York Times, but it could also be the manufacturers themselves. Right on the Cree web page talking about the Boston program it says “LED streetlights consume 50 percent or less energy compared to traditional streetlights”. I’m guessing that “traditional” is a significant qualifier in this statement, but I don’t know what they mean, and is the average person going to understand the distinction?

Flavor #2: “Numbers Crunch”

“Numbers Crunch” is the favorite flavor of LED product development engineers and marketers, especially those designing and selling LED lighting for streets and parking garages. They love to tell you about the amazing engineering that went into their fixture and how it delivers incredible numbers. The only thing they want to talk about is how the fixture delivers light to the ground, how awesome the uniformity can be, and how far apart you can space the poles. But what do these fixtures look like at night? Can I see well with them?

The true purpose of outdoor lighting is to make it easier to see at night, not to just deliver light efficiently to the ground. What we have seen with many LED outdoor fixtures is that they are very glary. Glare makes it hard to see. Sure, lighting the ground is important, but if the glare makes it harder to see, then it doesn’t matter how efficient the fixture is or how great the uniformity is. Sometimes I wonder if the engineers who designed these fixtures ever left their computer and stuck the fixture out on a pole at night and just looked at the thing!

So back to the Boston Common. I’ve looked at those six fixtures at night, and they perfectly illustrate what I’m talking about here. They all do about the same job of delivering light to the ground. But four of the six are terrible “glare bombs”. I don’t care what the numbers are, if the glare makes it hard to see and they’re unpleasant to look at.

OK, I’m done. Time to get a glass of cool clear water (or maybe a stiff drink!). What do you think?

Photos credit: Glenn Heinmiller / Lam Partners Inc