Following is a text version of a video about CALiPER Application Report Series 21 on LED Linear Lamps and Troffer Lighting.
Tracy Beeson, Lighting Engineer, Pacific Northwest National Laboratory: Fluorescent troffers are widely used in office spaces, meeting spaces, schools, all sorts of different space types. And they're a very efficient and cost-effective way to deliver high light output for all sorts of visual tasks.
Naomi Miller, Senior Lighting Engineer, Pacific Northwest National Laboratory: Troffers are the most common light fixture type in America. Fluorescent fixtures are designed around a fluorescent lamp that emits light in all directions. The optical system – the reflector – is designed to gather that light and redirect it in a very specific way, to spread the light evenly on the workplane below, which is the desktop. And not emit too much light close to horizontal because that's the light that usually is perceived as glare. If fluorescent is such a good technology, why are we looking at LED options?
If you're still using magnetic ballasts and T12 lamps, that's an old technology, very poor efficiency. If you're going to be doing a retrofit from a T12 option, it may make absolute sense to go to a good quality T8 LED tube. You're getting probably the same amount of light for sometimes half the wattage of your old T12 system.
Tracy Beeson: There are many different types of retrofit kits out on the market at the moment. There are a lot that are actually intended for fluorescent troffers, but what we're looking at with this study is specifically the tubes: one-for-one replacements, T8 tubes, so that we can look at the different optics and how it changes the aesthetics of the space, and how it changes the efficacy of the various luminaires.
Naomi Miller: We looked at the 100+ LED tubes on the market and we tried to characterize them.
Tracy Beeson: Some are surface-mounted diodes that you can see clearly through a clear lens. There are others that have a frosted lens. Others that are striated lenses, and there are also some that have remote phosphors. All of these lens types actually can cause some pretty interesting patterns on the walls or within the luminaire.
Naomi Miller: We looked at five different troffer types that are very typical in offices and classrooms, then we characterized the different kinds of LED tubes into basically three different flavors: one tube that emits a narrow beam of light, one tube that emits a medium beam of light, and then the third tube that emits a wide beam of light. We wanted to see efficiency, how much light out are you getting from the troffer itself for the wattage that goes into it. And, where that troffer is putting its light. Is it spreading it evenly, is it putting it down in a narrow pattern, is it putting light on the walls, is it not putting light on the walls?
Tracy Beeson: With the various light distributions of the LED lamps, you might be getting more light on the work surface in the space but the aesthetics of the luminaire and the aesthetics of the space might be compromised, which is why we're looking specifically at the distribution and how it might look to the eye.
Naomi Miller: We also wanted to see, "what does the troffer look like itself?" Because sometimes you can take an LED tube, put it into a fluorescent troffer and, whoa, it looks really different.
The vast majority of LED tubes are only emitting light downward and that means there's no light coming off the back of the tube so the reflector ends up being dark. There's no bounced light from above those tubes to help fill in the stripes appearing on the lens.
Tracy Beeson: So once you change the lamp in the troffer, it really does change the light distribution of that luminaire.
Naomi Miller: When we're putting in T8 LED tubes, we want to simulate the same pattern of light that we're getting from the fluorescent. We learned that the clear LED tubes tend to be a little more glaring and produce a narrower beam of light. Most of the luminaires we're looking at perform better if they have a frosted face on the tube. That just smears out the light a little more broadly and helps fill in those shadows.
The parabolic luminaires change appearance widely depending on which LED tube you put into them. The ones that have round, diffusing lenses immediately underneath the tube, not so much, you can't really tell the difference.
What surprised me is the range of products that are on the market — some very good LED tube products. Manufacturers that give you all the information you need to make your decision, like input wattage, color information – the color temperature but also color rendering index – light output once it gets mounted inside of a fluorescent troffer of a specific kind. But, we've found that a lot of manufacturers, especially ones that were fairly new to the market, didn't know what kind of information the end user needs or the specifier needs, and color is a really important piece of information on that.
Down the road, we're hoping to provide some guidance on which tubes and troffers, when paired together, give you the best lumens per watt and at the same time control glare and deliver the light where it's needed on the workplane. We basically want to help people have more success in retrofitting troffers with LED tubes.