How to choose the light technology for the job

You’ve bought only equipment with the Energy Star rating. You use power management. You’re careful about turning off your equipment at night. So is your office energy efficient? Not by a long shot.

While energy efficient computers are a hot topic right now, that’s only part of the picture. In the typical office power consumption is split about evenly between lighting, cooling and office equipment loads, says Peter Turnbull, senior program manager with Pacific Gas and Electric’s Office sector. If your office is like mine, you stand to gain quite a bit by paying attention not just to your IT equipment loads but your lighting and cooling as well.

Before my recent home office energy efficiency makeover, my office equipment consumed 2.2 kilowatt-hours of electricity per day, but my lighting – a whopping 370 watts worth for a 120 square foot space – consumed 2.96 kWh in an 8-hour work day. Every watt of power consumed in an office ends up as 3.514 BTUs per hour of heat. The waste heat generated by my IT equipment and lighting – about 5.2 kWh each day - also affected both my heating and cooling efficiency.

In the summer, the lighting and electronic equipment warmed up my office space, leading me to install a window fan that sucked up as much as 95 watts of additional power, adding .76 kWh (about 11 cents) per day to my power bill. This situation also caused problems in winter. The thermostat for the downstairs zone in my house is in my home office. The fact that the IT equipment was already warming the office meant the thermostat called for central heat less often, leaving the rooms adjacent to my office chilly.

All together, my office’s total power consumption came to 5.92 kWh a day. At 14 cents per kWh, I was spending $207 a year. As a byproduct of generating that power my local utility was exhausting 1,638 lbs of greenhouse gases into the air.

Through changes in my IT equipment and how I used it I reduced daily energy use to .63 kWh (see the story. After optimization, my IT equipment represented just 12% of total electricity use during the summer.

Light deals

Then was time to tackle the lighting issue. “One half watt per square foot is attainable,” says Turnbull. The California standard for office buildings, considered leading edge, is 1 watt per square foot. My office was at just over 3 watts per square foot.

I started by replacing the dual 60-watt overhead lamps with a single 23 watt (100 watt equivalent) compact fluorescent bulb. Next I brought in a new 10/20/32 watt (50/100/150 watt equivalent) 3-way MaxLite floor lamp and matching table lamp that use circular fluorescent tubes. (I bought mine through a utility-sponsored program called NH Saves but you can also buy them from the nonprofit Energy Federation Inc. The program, which subsidizes lamps and fixtures, brings the cost down to about wholesale, according to Public Service Company of New Hampshire. In this case, a solid, nickel-plated the floor lamp cost just $35; the table lamp $25. Check with your utility for similar programs.)

Because I have two long desk surfaces I needed another lamp for reading. At first I tried a compact fluorescent bulb in my desk lamp. Fluorescents are highly efficient, using about 75% less power than an incandescent bulb to generate the same amount of light, but they’re not always a good fit for task lighting. Both fluorescent and incandescent lamps tend to over light work surfaces. Also, both fluorescents and incandescents radiate the light produced in all directions. “The distribution of that light is somewhat problematic. You don’t get the light here you need it,” says Turnbull. That’s an important consideration, since the key to efficiency is to light the task, rather than the space. For this reason, the future of task lighting, he says, is light-emitting diodes (LED).

The LED advantage

Most rooms are over lighted, and may produce too much light on some surfaces and not enough on others, says Jeannine Fisher, director of marketing at Finelite Inc. in Union City, Calif. On a reading surface, fluorescents can create glare on documents. In contrast, LEDs produce highly directional lighting – all of the light goes where intended. “For an equivalent light output it’s about a 50% power savings,” she says. Unlike fluorescents, LEDs contain no mercury and better quality lamps can last up to 30 years.

Because of the greater efficiency of LEDs and the fact that the light is highly directional, a 6 watt LED fixture can replace a standard 32 watt under-cabinet “T8” fluorescent tube when mounted over a desktop, Fisher says. The 6 watt LED doesn’t produce the same light output, she admits, but it doesn’t have to. “The fact is that the 32 watt fluorescent is over lighting the task,” which adds glare, she says. “With lighting design you want to minimize contrast. You want to get rid of shadows but you don’t want areas that are very bright relative to adjacent spaces.”  With proper task lighting, ambient lighting in a room can also be reduced. LEDs are ideally suited to that function.

However, LED technology is still evolving. “There have been big improvements in the amount of light per watt,” Fisher says. But LED lighting is also expensive, and cheap models may not have the same light quality and can lose their light balance and suffer a shorter lifespan if the control chip isn’t kept cool.

I started with an inexpensive unit: an 11 watt Power Bright 198 LED that I borrowed from my local Green Energy Options in Keene, NH. The three-foot long tube is about the size of a fluorescent bulb and is designed to mount under the cabinet above my desktop. This no-frills model has no switch but costs $40 –a good price for an LED of this size. Another model I tested is designed a direct plug-in replacement for a 32-watt T8 fluorescent tube, and fit into a four foot ceiling fixture. Those sell for $32 each.

Luminance claims vary. While the 11 watt unit is supposedly equivalent to a 75 watt incandescent, the 14 watt T8 replacement is designed to replace a 40 watt fluorescent in terms of light output. I tested the former, and it was more than adequate as a substitute for my 100 watt incandescent desk lamp. I pay my local utility $.14 cents per kWh for power. At that rate the 91 watt power savings, assuming would cut $25 annually off my power bill.

Better quality LED desk lamps are more expensive. The 5 watt Sylvania Brilliance desk lamp, which I didn’t test, sells for $89.99. Finelite Inc. just launched a line of ultra modern, executive desk lamps and under cabinet lights. Prices range from $139 to $283, but for the money you get the latest technology, which the company claims produces superior light quality and greater longevity than some of the less expensive LEDs on the market.

I tested Finelite’s PLS 9, a 9-watt desk lamp that uses just 9 LEDs versus 198 for the 11-watt LED tube light. Fisher says the unit produces light equivalent to a 100 to 150 watt incandescent desk lamp – twice what the claims for the tube light. Why the difference?

Finelite

This Personal Lighting System 9-Watt desk lampfrom Finelite Inc. uses nine 1-Watt LEDs to produce light output equivalent to that of a 100- to 150-watt incandescent, the company claims.

The technology inside the less expensive lights, such as the tube light I tested, is at least one generation behind what Finelite offers, says Pablo Fleishman, owner of Green Energy Options.  

The Finelite lamp’s color balance was more natural. When compared to the tube light the color appeared tilted a bit toward the yellow end of the spectrum. It was warmer than the low-cost tube LED, which cast light in a faint, grey-blue hue. I found both units acceptable, however. Either will do a good job illuminating your desk. Other than color balance. I didn’t see a big difference in light output. Overall I found LED lighting to be more uniform and easier on my eyes than either the fluorescents or incandescent bulbs. I wanted the Finelite unit, but the $285 price put it firmly in the luxury category. In the end I chose the cheaper, 11-watt LED and added the cool Finelite on my holiday wish list.

replacement


This 11 watt LED tube light replaces a 48-inch, 32-watt fluorescent bulb. Image courtesy of Green Energy Management, LLC.

 
The final analysis

In my final configuration I went with a single 23 watt compact fluorescent in the ceiling fixture, operated the table and floor lamps at the middle (20 watt) setting and used the LED as a task light on the desktop as needed. I’ve found that on sunny days I don’t really need the overhead light at all.

I did discover one annoyance with high efficiency lighting: My solar calculator doesn’t work anymore. Neither the 11 watt LED nor the table and floor lamps operating at the maximum 32 watts produced sufficient light to power it.

My total lighting load now varies from 40 to 74 watts. Worst case I am still saving 296 watts on lighting, which translates to about 615 kWh a year, or $83. That’s also 1,040 fewer BTUs per hour of waste heat radiating into my office, and I’m doing my part for the environment. My office office’s reduced power means 682 fewer pounds of greenhouse gases will go into the atmosphere in the coming year.

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