Lighting: Technology and Design Can Combine to Increase Energy Efficiency
By James Benya - August 2005 - Lighting
During the past 10 years, there has been an understated revolution in office lighting. New lamps, ballasts and optics dramatically reduce energy and maintenance costs. New lighting fixtures can be used in attractive designs and accommodate even the lowest ceilings. And a combination of convenient lighting controls and design approaches offers the potential to improve occupant productivity and satisfaction. In other words, today’s lighting systems are a giant leap forward, making it worthwhile to use them for new buildings and to seriously consider replacing rather than retrofitting older installations.
Is it time to upgrade a space, even a relatively new one? A review of recent advances in technology and key design principles can help facility executives make that decision.
T-8 and T-5 Lamp Technologies
To begin, the lighting system should employ the highest possible source efficacy. Today’s top products are the “high performance” or “super T-8” and T-5 lighting systems. The standard 4-foot T-5 lamp and ballast system operates at up to 99 mean lumens per watt (MLPW) and the 4-foot “super T-8” can achieve 101 MLPW. Another option to consider is the T-5HO system (83 MLPW). The only other light source that comes close is the high wattage ceramic metal halide system 320 watts and larger. Compact fluorescent lamps, low wattage metal halide and other sources should be limited to special areas.
To identify a super T-8, look for lamps that are at least 3100 initial lumens and have a barrier coat design and high lumen maintenance.
Also worth considering is the 30-watt T-8 lamp and ballast system, although it is available only as instant start — one of several reasons a facility executive might prefer the standard 32 watt lamp. Other reasons to select the 32-watt T-8: The low wattage T-8 lamps have fewer lumens per watt and are not universally compatible with all T-8 ballast types. Also, they may exhibit longer warm-up times and be more sensitive to ambient temperature.
Efficient Electronic Ballasts
Yes, there is now an “efficient electronic” T-8 ballast that uses 7 to 9 percent less power than a regular electronic ballast. These ballasts are available in both program start (for long lamp life, especially when a motion sensor is being used) and instant start (for long hours of continuous operation). Note that the 30-watt T-8 lamp is instant start only — one of several reasons a facility executive might prefer the standard 32 watt lamp.
For T-5 systems, both program start and instant start ballasts are available.
With high-intensity-discharge (HID) lamps, electronic ballasts are just becoming common. It is now possible to employ electronic ballasts for metal halide lamps up to 400 watts, and they make a huge improvement in lamp performance. As a rule, use electronic ballasts for all fluorescent and HID lamps if possible. In almost every case the electronic ballast ensures the highest mean lumens per watt, both by inherent efficiency and, in the case of metal halide lamps, by better lamp power management. But remember — when the goal is generating the most light per watt, only T-8, T-5, T-5HO and high wattage metal halide systems (250-400 watt) are good choices.
Efficient Luminaires or Optical Systems
The next step is to get every lumen possible out of the fixture. Efficiency is given with each fixture’s photometric report, and it offers a quick way to compare products. But also remember to check the fixture’s coefficient of utilization report, as the shape of the distribution curve may also be important. This is especially true for indirect and direct/indirect lighting systems, where the straight-up candlepower is not as effective as candlepower off to the sides.
A couple of years ago, a major manufacturer introduced a 32-watt compact fluorescent downlight that was arguably the most attractive and best-shielded open downlight on the market. But this particular downlight was only about 40 percent efficient, and the typical efficiency of competing products was 55-60 percent. For the same light level, it would have been necessary to increase lighting power in downlighted spaces by 50 percent. When buildings are being designed at 0.9 watts per square foot and less, this performance is not acceptable and it will be necessary to use the more generic and efficient downlight in most of the building.
Color, texture and the use of natural materials are all part of good architecture and interior design. Yet for efficiency of lighting, a white box is much better. The ordinary give-and-take between architecture and lighting must accept some new limitations to get the most efficient results.
First, consider the ceiling. If an indirect or direct/indirect lighting system is being used, the ceiling must mostly be white, flat and high reflectance. Save the wood panels and open structures for the lobbies and a few other places in the building. Ceiling plane reflectance of 80 percent or more is essential. In a small space, the difference between very light finishes and a relatively dark interior design means adding about 0.5 watts per square foot in a darker room, which is a very large amount when the design is only 0.8-1.0 watts per square foot.
Also, consider other room surfaces. Upper walls are second in importance to ceilings, and they should be light colored as well. Rich finishes and other surfaces of low reflectance can be used below eye level with a minimum negative impact on interreflectance. The floor can have a significant impact in a downlighted space, like a gym, but it is less important in offices where furniture covers much of the floor plane.
Use All Other Light sources Sparingly
There are many spaces and tasks for which the T-8 and T-5 lamps just don’t work. Consider (roughly in descending order of preference) T-5 twin lamps, high wattage compact fluorescent lamps, low wattage metal halide lamps and even the occasional halogen IR lamp. Try to avoid ordinary probe start metal halide lamps, low wattage compact fluorescent lamps and ordinary halogen and incandescent lamps.
Often the biggest battle is in designing premium spaces such as boardrooms, lobbies and other high-end corporate space. Interior designers and architects will want to employ rich, dark finishes and tungsten light sources. Use of low efficiency lighting should be very carefully restricted — as a general rule, no luminaire should be rated more than 100 watts. Encourage the designer to try to find efficacious decorative lighting — even table lamps are available today with hard-wired compact fluorescent lamps.
Controls Could Be King
Remember, energy equals power multiplied by time. Use control systems to reduce on-time or power or both. These are energy savings just as much as any of the other recommendations, although they don’t show up in the watts-per-square foot conversation. That is because energy codes and incentives tend only to reward power savings. Because most codes mandate automatic shut off controls for lights, the savings are required and don’t count towards code compliance or LEED (Leadership in Energy and Environmental Design), the green building rating system developed by the U.S. Green Building Council.
However, advanced controls including daylighting controls and other approaches exceeding code can still be used to achieve energy savings that can in turn be used for LEED or incentive credit. California Title 24 still offers effective power reduction values for automatic daylighting control, and the savings from daylighting or other controls exceeding code can be counted towards energy savings in the LEED system.
In the 1990s, utilities across the country paid rebates to customers who retrofit their lighting. This was called demand side management and was based on the premise that “negawatts,” or saved watts, were cheaper to buy than “megawatts” of generating capacity. Today, rebates are still available, although because of deregulation, the amounts vary considerably. The amount of the rebate is usually at least 20 percent of the initial cost of the lighting improvements, though in some cases it can be as high as 100 percent of the first cost.
Always check with the utility representative before hiring a contractor. Failure to follow incentive-program rules can result in no rebate at all. However, for those smart enough to take advantage of it, a lighting rebate is literally free money, often “buying down” the cost of a lighting improvement to an 18-month payback or less. In these days of a shaky economy and low rates of return on investments, a virtually guaranteed annual rate of return of at least 67 percent forever is mighty attractive.
For instance, Utah Power offers wonderful rebates on modern lighting systems. In a new building, their current rebate program can offset up to 100 percent of the incremental cost of efficient lighting as compared to lighting that merely meets code. It is hard to imagine a building owner who would not want to take advantage of no increased first costs and significantly reduced future costs.
Of course, improved lighting can bring more than just energy savings. Today’s lighting technology and design strategies can give a space a contemporary look, support employee productivity and boost lighting quality. To take full advantage of lighting opportunities, facility executives will need professional help. Try to engage an independent consultant or firm not actually involved in the supply of product or labor to the final project. Expect the specialist to have one or more significant credentials such as LC (Lighting Certified by the National Council on Qualifications for the Lighting Professions), CLEP (Certified Lighting Efficiency Professional, a program of the Association of Energy Engineers), CLMC (Certified Lighting Management Consultant, a program of the interNational Association of Lighting Management Companies) and IALD (member of the International Association of Lighting Designers).
James Benya is principal of Benya Lighting Design in West Lynn, Ore. Stefan Graf is principal of Illuminart lighting design in Ypsilanti, Mich. Both are professional members of IALD, the International Association of Lighting Designers.
Find us on Google+