Revised April 2013
I am looking at upgrading my office building's fluorescent lighting, and a sales rep is encouraging me to use T-5 technology, but I will need all new fixtures. What are the advantages of T-5 technology, and is it the most energy-efficient technology, as he tells me?
Depending on what your current lighting system is and how extensive your renovation will be, you have many options. Your decisions should not be made only on the basis of a lamp's energy efficiency, although it is an important consideration, because it may not be an indication of how efficiently the light may illuminate your target area. The proliferation in the market of fluorescent lamps and ballasts, which are not all interchangeable, allows for many options as well as confusion, for the buyer. In addition, LED1 technology is also available for general office lighting.
Light level recommendations and lighting power allowances have probably changed since your current system was installed, and how you use the space may also have changed. Today there are additional lighting controls required by codes as well, so before you plan changes, check to see what your jurisdiction requires, and if requirements may change in the near enough future to impact your project. Depending on the long term plans for your facility you may be interested in a cohesive lighting plan that involves more than changing your lamp technology. Be sure to consult your utility to see what help and incentives they may provide to help with your project.
Office lighting not only provides a good visual environment for the occupants; it contributes to the company's image and the overall mood of the space, through both the lighting quality and the fixture styles. In addition to the efficacy of the lamp, the fixture style and efficiency will affect how much of the light emitted by the lamp makes it out of the fixture and onto the targeted area, which can vary a lot.
If you plan to retain your current layout, your light fixtures are in good condition, and you want to keep them, T-5 technology will not be suitable, because it is a shorter than 4-foot, metric-based product that will require new fixtures. But, there are many T8 lamp and ballast options to meet your needs very efficiently. If you plan to install new fixtures anyway, then T-5 technology may be for you. At 5/8 of an inch in diameter (the “5” in T-5), it is a skinny lamp that can fit in sleeker fixtures than the old T-12 or the newer T-8 lamps, making it especially useful for cove lighting and applications in tight spaces. T-5 technology is available in standard output and high output (T5HO) models.
Because small diameter lamps have much less surface area over which to disperse the light, T-5 light is also very bright, about twice as bright to look at as that of similar output T8 products, so fixtures with good optical design are needed to prevent direct viewing and to control glare while light is dispersed. Indirect and indirect/direct fixtures bounce all or much of their light up to the ceiling which reflects it down to work surfaces and creates a softer, less glare-producing light than most downlight fixtures do. In addition to lighting the ceiling, indirect lighting limits lamp reflections on computer screens, a problem often handled by parabolic fixtures for T12 or T8 lamps, which produced dark ceilings and cave-like atmospheres, requiring additional lighting for upper walls. In order to provide enough light to travel the extra distance for uplighting, more light needs to be produced from the lamp. The T5HO is commonly used for that purpose. There are new fixtures for T5 and T8 technology, referred to as volumetric fixtures, which spread light across the room and reduce reflections below, that are being installed in many offices due to their high efficiency and good light distribution. When T-5 lamps first arrived on the American market there was a limited amount of fixtures available to utilize them because of the length as well as the optics needed to control glare, but that is no longer an issue. In addition to office type lighting, high-bay applications often use T5HO lamps because their brightness allows one lamp to replace two standard T8 lamps, sometimes allowing for a smaller fixture and fewer lamps to maintain.
For years T5 technology provided only two wattages, 28 for the standard lamp and 54 for the high output lamp, but recently several energy-saving models of the T5HO (44-51 watts) have become available, using less energy for more light, or even less energy for slightly less light, and, at least one 25 watt model with the same light output as the 28 watt model. There is also an 84 watt, very high output T5 lamp.
Linear fluorescent lamps are designed with an optimum operating temperature and will maintain 90% of their output over a range on either side of the peak, losing more out of that range. T5 technology peaks at a higher temperature than the T8s and has been used mostly indoors in the past where it is warmer. Amalgam technology widens the temperature range of 90% output, allowing direct competition with metal halide lamps in unconditioned spaces, though it does noticeably slow the instant on/off function associated with linear fluorescent lamps and makes it less responsive to dimming as well.
Selecting reduced mercury lamps may save on disposal costs. Local regulations vary, so enquire.
T5 systems use programmed start ballasts that provide soft-starts in order to provide less shock on starting, thus extending lamp life, and, on 12-hour starts with extended life lamps they are rated at 60,000 hours. These ballasts make the system compatible with the frequent switching due to the use of occupancy sensor controls, daylight harvesting, or other inputs, depending on the control systems and owners' desires, without substantially affecting lamp life from continuous operation (when it lasts the longest). Dimming is also available from programmed start ballasts. Alternatively, an amalgam based lamp is only 35,000 hours, and standard T5HOs have about 40,000 hour lives on twelve hour starts. Lamp life is important because it directly impacts maintenance costs, and the more disruptive to office functions lamp changing is, the higher the impact on the budget.
Ballasts with end-of-life sensing are available to reduce lamps breaking at failure and may need to be specified. Ballasts for T5 lamps drive one or two lamps, as opposed to those for T8s which may drive up to four lamps.
T5 lamps are known for their good color rendering and a CRI2 of 85 is standard.
There is a wide range of color temperatures3 available from 2700K to 6500K, and whatever you decide on, make it clear to staff (and your future replacement) with documentation that replacement lamps must match the originals. 4100K was the traditional temperature for office and commercial lighting from the time of the T12s, which were not known for good color (CRI 62), and many facilities mixed warm and cool whites in an attempt to improve the appearance of occupants, giving the fixtures an unmatched look in the process. T5 lamps with 4100K temperatures have very good color thanks to the 85 CRI, and many facilities use even cooler lights, like 5000K or higher. When viewed near a 4100, the 5000K will look bluish and the 4100K will appear warmer and yellowish, yet the same lamp next to a 2700K will appear bluish. Color temperatures can vary and all appear as white light to occupants as long as all the lights in the same view match. The cooler temperatures have been found to improve visual acuity when less light is actually delivered due to the way our eyes work, and to increase energy levels of occupants as well, impacting productivity in businesses, sales in retail and learning in schools. The Federal Energy Management Program of the U.S. Department of Energy recommends that high color temperature fluorescent lighting (5000K) be used in federal buildings to allow for a 20% light level reduction in T8 systems.
When it comes to the question of the best energy-efficiency there is no clear-cut answer. Fluorescent lamps produce a certain number of lumens per watt on a particular ballast, but fixture type will play a huge role in how many of those lumens escape the fixture into the general space and onto the intended target. Ballast type will also determine control type options, and, the control system could reduce energy use through dimming or switching differently from your current system, based on various inputs.
T8 systems tend to have slightly higher lumen maintenance at 97%, while the T5s are 95%, both excellent, and the difference is not likely to be noticeable. One lamp in a fixture with good optical design will not lose any light distribution due to interference from a second, third or more lamps, but more lamps on one ballast, and fewer fixtures, have another kind of economy. Fewer fixtures cost less but unless they also produce even distribution throughout the space, the lighting quality may suffer. Fewer lamps may cost less, but T5 products tend to have a premium cost associated with them, and they may not be stocked locally.
The capacity to provide just the right amount of light in the right place and time is the goal of lighting system planning. Being able to maintain the design through lamp, and possibly ballast, changes is easier if only one lamp type is stocked for spot replacements, ideally rare, between group relamping.4 With a T8 system the amount of light can be fine-tuned by selecting ballasts with very-low, low, normal, or high or very high output, and once installed, they may never be replaced before the lighting is converted to another technology, although the availability of several low wattage lamps are also available for further control. With T5s it is typically the lamps that would be varied, and they are likely to be replaced one or more times before a technology switch, in which case if multiple types are used, getting them in the original design may be tricky. Some ballast manufacturers will provide customized ballast factor units for either technology. Again, instructions should be left for any staff who may be charged with replacing a ballast so they know which ones go where if they are not uniform.
Today the world of lighting is rapidly changing, and while a high performance linear fluorescent system is hard to beat for efficiency and economy as well as high quality light, LED technology is expected to take over most of the lighting applications over the next two decades or so. Lamp life is one of the big sellers for LEDs (ranging from 35,000 hours to 50,000 hours and constantly climbing) for reducing maintenance, but as you can see from the numbers above, some fluorescent systems last just as long as many, and longer than some. Plus, none of the LED systems have been in real world use long enough for us to know if the life expectations will be reached with enough lumen maintenance and original energy savings. Unlike most traditional lamps that quit working when they fail, LEDs slowly fade away, finally being "on", but not providing enough useful light to do the intended task.
A switch to LED technology now (4/2013) would be best done with dedicated luminaires, not fixtures with tradable parts like lamps and ballasts available from multiple sources. It is also recommended that you do a full mock-up of the application before committing to a large purchase of products (always a good idea, but especially so with LED products) as they vary widely in performance. You would also be wise to determine what qualified lists the products you are considering are on, and, again, consult your utility for some assistance with this project. Once the unit fails it would be replaced with another complete unit. It is hard to know just what systems will come out on top of the new LED world except that it is changing nearly everything about lighting as we’ve known it.
One feature that is rapidly gaining interest and unique to LEDs is "Kelvin changing", or color changing lamps that with the right lamp and controls can be user tuned to warm or cool white and in between. This tuning can be done with fluorescent systems using different lamps, but LEDs can use the same lamp to do it. Personal control of lighting has been shown to be valued by occupants, and this provides even more control and comfort, both of which may lead to longer employee retention and increased productivity, although those are hard to measure.
As you can see, there is more to selecting your next lighting product than the energy-efficiency of the lamp, and ideally you, or a consultant, will narrow your choices based on all of the factors, then see your options in actual use before committing to one.
ASHRAE Advanced Energy Design Guides (AEDG) are free, downloadable, whole building guides for new construction or major remodels that include lighting information. The 50% Advanced Energy Design Guide for Small to Medium Office would be helpful.
DOE. Federal Energy Management Program. Spectrally Enhanced Lighting.
The following information resources are selected from the E3T Energy Efficiency Emerging Technologies Database, a collection of practical, commercially available, not-yet-widely-used energy efficiency technologies that are regularly reviewed and evaluated by energy experts and engineers.
- Bi-Level Office Lighting with Occupancy Sensors, Auto-On 50%
- LED Linear Commercial Office Lighting (including troffers and pendants)
- Low-Cost Energy Management and Control System for Small to Medium Commercial Buildings
1 Light emitting diodes, commonly called LEDs, are electronic light sources. They use a driver for similar functions as a ballast. Though there are mature products on the market, there continues to be much growth in products and controls as well as standards to regulate them. There is wide variation in the market, and change is rapid. Due diligence is required if the use of this technology is under consideration.
2 CRI : Color Rendering Index is a measure of how accurately colors appear to the viewer compared with daylight at noon or a standard incandescent lamp, both rated at 100. Above 60 is usually good for general exterior lighting or storage areas. Above 80 is very good; 90 and above is excellent. In retail, graphic design, and other applications where color matching and identification are critical, 95+ should be used. Some energy efficiency is often a trade-off when measures are included in lamp technology to improve the color.
3 Correlated color temperature (CCT), often just called color temperature (CT), is an indicator of how warm or cool the color of light appears, with yellowish light being warm, and bluish cool. The number assigned is indicated in Kelvins (K) and is an absolute number relative to a black body radiator (like a metal rod being heated to red hot, then white hot), and the higher the number, the cooler the light. 2700K is the color of standard incandescent light. Above 5000K is the realm of daylight. Any two colors in the same view will appear yellowish or bluish relative to the other, but alone could appear white. Paired with CRI, CCT is used to describe how colors of objects will appear under a specific light source, technically only of the same lighting technology family but practically used for lack of anything better even when comparing light sources.
4 Group relamping is a recommended lighting maintenance plan that replaces all the lamps in a facility or floor, etc. at the same time. This is usually calculated at about 70% of the lamp life of the system to prevent too many spot failures before relamping. Light levels can be maintained, and through bulk purchasing, labor, and disposal costs, it is more economical.