Fluorescent troffers are the single most common fixture type in commercial spaces in North America. Offices, retail, education, medical centers, laboratories, retirement homes – the list goes on – most utilize troffers in their facilities. The vast majority of currently installed troffers have fluorescent tube (T5, T8, T12) light sources.
Today, the LED alternative to fluorescent, whether a new LED troffer or a retrofit kit, will yield a 40% higher efficiency than most fluorescent and a 20% to 50% longer life. An LED upgrade translates into lower energy bills and reduced maintenance costs for the facility.
If you’ve been unsure about how to proceed in transitioning to LED, the following steps will give you a path that covers all the important factors in the decision making process.
Step 1: Determine Light Levels
Key Assumption: The existing layout of the fluorescent troffers will not change.
If current fluorescent light levels meet the needs of the space and occupants, then you will want to make sure the replacement LED troffers match those levels.
First, in a typical space that is to be converted to LED, use an illuminance meter, at night or with dark shades drawn, to measure light levels (usually in footcandles) on the surface of desks or other areas where tasks are performed. This measured existing light level will be used later as a comparison with the light level provided by test LED troffers you install.
Second, consult the specification sheet of the existing fluorescent troffers.
Find the value for light output of the fixture (in lumens). This value will include the fixture lens or louver, lamps and ballast. In the example on the left, for a 2 lamp, 2×2 lensed troffer, each lamp produces 2800 lumens (total of 5600 lumens). Apply the fixture efficiency of 76% to get actual rated initial lumens of 4256 for the new fixture
Lumen depreciation of the lamps will cause this 4256 lumen output value to decline over time. The mean lumens for a fluorescent lamp is assumed to occur at about 40% of rated lamp life. At that point a minimum 5% reduction in initial lumen output of the fluorescent lamps is typical. This is important because the measured light levels for the space you got from the light meter will most likely reflect fluorescent lamps operating at a 5% reduction (at least) compared to the initial light output assumed by the specification sheet.
So, unless you know the fluorescent lamps in the existing troffers have been recently replaced, the calculation will look like this: 5600 lumens x 0.95 (lamp lumen depreciation) x .76 (fixture efficiency) = 4043 lumens per fixture.
Finally, survey the occupants to determine if the existing fluorescent light levels are too high, too low or about right.
You might tempted to skip this initial light level evaluation, however it’s risky to go blind directly into selecting an LED replacement troffer based on your “estimate” of an equivalent fixture.
Step 2: Select an LED Troffer
Locate a selection of LED troffer manufacturers by going to the web sites of lighting manufacturers you are familiar with or search the web for LED troffers. Once you have several options, consult the spec sheets to find LED products that have initial lumen output that comes close to the calculated lumen output of the existing fluorescent troffers (in our example, that value is 4043 lumens per fixture).
Example: From a specification sheet for a 2×2 LED recessed troffer, you see a range of lumen packages. The highlighted fixtures show lumen output levels close to the 4000 lumens calculated from the existing fluorescent fixture spec sheet in our example.
Note also the LPW column – lumens per watt. Fixture efficacy is an important part of fixture selection and it is discussed below.
After finding several LED options (ideally from at least a couple of different manufacturers) with the light output you need, fine tune the options by comparing some important characteristics.
Most utility rebate programs apply only for projects where LED fixtures are used that meet Design Light Consortium (DLC) requirements. If rebates are critical for the project to be cost effective, DLC qualified product is essential.
High luminaire efficacy (lumens / Watt) is built-in to the DLC qualification, so if you are considering only DLC rated fixtures, the only additional decision is filter the options to the fixtures with the highest efficacy. According to the Lighting Energy Alliance, “using a troffer with an efficacy 15 lm/W greater than another troffer can decrease the lighting power by about 20% in an open office.”
Some manufacturers offer tunable drivers as an upgrade option. The advantage of a driver that allows light level adjustment in the field after installation is significant. With a range of available light levels from each fixture, driver tuning can increase or decrease the output to very closely match the light level of the fluorescent troffers (measured by an illuminance meter) or to achieve a different light level to meet the needs of the occupants.
Color Temperature (CCT)
Most commercial fluorescent troffers use lamps with color temperature in the range of 3000K to 4000K. Unless the occupant survey of the lighting suggests a different color temperature should be used, simply match the CCT of the new LED fixtures with existing fluorescent lamps.
If the existing fluorescent troffer system is connected to occupancy / vacancy sensors or photocell controls, it’s important to confirm the compatibility of the new LED fixtures with the existing control system. If there are no existing controls, you have the opportunity to further increase the energy efficiency of the new LED system by adding them. Some LED fixtures can be ordered with integrated sensors, simplifying the installation without additional wiring.
Cost / Warranty / Product Reviews
Get quotes on the LED fixtures (with options) you’ve identified as a good fit for your application. If you can find reviews from other facilities that have installed the LED fixtures being considered, this information can be useful in making a final decision. Most LED fixture manufacturers now offer product warranties in the range of 5 to 6 years.
Step 3: Purchase and Install Test LED Fixtures
Before buying a truck load of LED fixtures, it is always smart to install one or two and compare, side-by-side, the illumination with the existing fluorescent fixtures. Having occupants of the space give feedback is also a good idea. The results of this in-the-field testing and feedback will either confirm the LED troffer selection or will point to where adjustments need to be made.
For many facilities looking to retrofit / replace existing fluorescent troffers, the steps outlined here should provide a sound basis for selecting LED troffers.
For extensive remodel projects, a more sophisticated approach requires using photometric software to optimize fixture layout and illuminance levels. A lighting designer may be a necessary addition to the project team.
For more detail on all aspects of LED troffer selection as well as guide to calculating energy savings and payback, download this publication from the Lighting Energy Alliance at Rensselaer Lighting Research Center, a collaboration of researchers, utilities, ESCO’s and energy efficiency agencies.
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