Fluorescent vs. LED Lights

As school budgets and energy consumption continue to be hot topics; and the IgCC (see The Future of Building Green) is requiring both dimmable light fixtures and occupancy sensors, selecting the proper lamps for your school should be an important topic of discussion. The two biggest players in the game are Fluorescent and LED – both viable options, depending on your district’s goals.

Important characteristics that will apply to both lamp types are as follows:

Lumens – the amount of light emitted per second (light output)

Efficacy – is the factor of lumens per watt consumed

Color Rendering Index (CRI) – The measure of the ability of a light source to reproduce the colors of an object as compared to a natural light source; expressed on a scale of 0-100 with 100 being daylight. The available range is relatively the same (50-90) in both fluorescent & LED lamps so I won't compare them, but it's important to speak with your architect and electrical engineer about your expectations.

Color Temperature (CCT) – The numerical measurement of a light source’s color appearance, measured in degrees Kelvin. Think about fire, as it begins to burn, the flames are red & orange, but as it gets hotter, the flames turn blue & white. Lamps are the same, cooler temperatures are warmer in color and warmer temperatures are cooler in color. Similar to CRI, the available ranges are the same (2500K-6500K), you just need to discuss options and related costs with your architect.

Linear Fluorescent Lamps: The Contender

This is the MOST common lamp used in commercial and institutional buildings. This fact alone is what makes them so affordable - the technology is mature and the market stable. The basic construction of a linear fluorescent lamp is a glass tube coated on the inside with a phosphor, filled with a mixture of argon/krypton gases and a tiny amount of mercury. Light is produced when the phosphor coating is excited by the UV radiation from the electrode/mercury combination. It is very important to ensure lamps are disposed of properly because while the amount of mercury is small, as thousands of lamps end up in landfills the hazard increases. Please contact your city for proper hazardous waste disposal. Lamps are identified based on their shape and diameter – meaning if the Tube is 1” (8/8”), it is a T8. Standard sizes used in schools are T12s (although these are being phased out for inefficiency, older buildings may still have them), T8s and T5s. It is important to note that ALL fluorescent lamps require a ballast (a mini transformer) to provide voltage to start the lamp and regulate the electrical current during operation. T12s use electromagnetic ballasts and T8/T5s use electronic ballasts that are about 40% more efficient than electromagnetic. An energy conservation option for older buildings with tight budgets is to convert all T12 lamps to T8s; just be sure the fixtures and ballasts are compatible with the new lamps. An uncommonly known downfall of linear fluorescent lamps is their sensitivity to temperatures. Fluorescent lamps will not light up in extreme cold or hot temperatures because the mercury vapor pressure is dependent on the ambient operating temperature of the lamp (not room temperature, but the temp around the lamp itself in the fixture). The lamp life can also be affected by how often the light is turned on & off. Lamp life is based on a three-hour burn cycle, three-hours on and 20-minutes off. Operating lamps at a longer than three-hour burn cycle will increase lamp life (up to 36,000 hours); conversely, operating lamps on shorter burn cycles will reduce lamp life.



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Image courtesy of US Dept. of Energy

Advantages:
Mature Technology = Low Cost
Low Cost per Lumen
Extensive Fixture Options

High Efficacy (30-110 lumens/watt)

Long Life (7,000-24,000 hours)

Disadvantages:

Requires a ballast

Added cost for dimmable ballast

Temperature Sensitivity
Lamp life affected by how often it's turned on/off
Must be disposed of properly (mercury & gas)

Delayed turn on - flicker

LED Lamps: The Challenger

Light Emitting Diodes (LEDs), also known as Solid State Lighting (SSLs), are highly sought-after for their reduced energy consumption. Multiple LEDs can easily put out the same amount of light as fluorescent tube for a fraction of the wattage. An additional cost savings that we stumbled upon in a recent project was that while one electrical panel can typically support 25 linear fluorescent troffers (the 2x4 fixtures), the same panel could support 75 LED fixtures – that’s a significant initial savings in electrical equipment. That’s right, I said it: initial savings. Every time someone brings up LED lights their first reaction is, “I know they’re more energy efficient, but it costs SO much initially.” Initial costs are dropping slowly and there are some factors that are making the competition a little closer. I mentioned fewer electrical panels for the same # of fixtures. If you’re familiar with the new energy code (IECC), it has defined that any lights within daylight zones must have dimmable controls that are independent of the general area lighting. In order to make a fluorescent lamp dimmable, there is a major change in the ballast that increases the cost – almost equal to that of an LED which is inherently dimmable. Another thing people are concerned about is the color of LEDs. Long gone are the days of blue-tinted light, unless that’s what you want. In fact, LEDs are available in saturated colors (Red, Green, Blue, etc.) and various temperatures of white light – some achieving CRIs of 90+. The final benefit I’m going to discuss is the heat emitted from LED lamps. A typical linear fluorescent emits about 30 btu’s/hr while an LED only emits 3.4 btu’s/hr. This could translate into a minor adjustment to the cooling load for the building – something to discuss with your mechanical engineer.

Advantages

Image courtesy of US Dept. of Energy



High Efficacy (25-100 lumens/watt)

Long Life (35,000-50,000 hours)

Inherently dimmable

Reduced energy consumption (~1/2)

Mercury-Free

Less Heat Build-up (~ 1/10^th)

Immediate On

 

Disadvantages

High initial cost

Directional nature – requires more lamps to get ambient light effect

Limited fixture options (troffers)

Resources:

U.S. Department of Energy - http://www1.eere.energy.gov/manufacturing/utilities/fluorescent.html                                           http://www1.eere.energy.gov/manufacturing/utilities/solidstateled.html

Eartheasy - http://eartheasy.com/live_energyeff_lighting.htm#1c

Comparison Chart: http://www.designrecycleinc.com/led%20comp%20chart.html