Ask The Experts
Click on the following questions to see our experts' opinion. If you have a question that's not listed here, please contact us.
I have a hard time keeping my exit signs lit. It seems like they are always burning out.
I’ve heard about induction lamps. Are they a good technology?
Do reflectors increase the efficiency of the light fixture?
The lights on the outside of my building go on and off, seemingly at random. What’s happening?
What’s the difference between a T-12 and a T-8 lamp?
What about T-5 lamps? Are they more efficient than T-8 lamps?
What do all the lamp color notations mean? What’s the difference between cool white and 4100K?
How many jugglers does it take to change a light bulb?
Q: I have a hard time keeping my exit signs lit. It seems like they are always burning out.
A: This is one of the slam-dunks of lighting. Replace your exit signs with LED signs. They will last almost forever, they will look good, and they will use less energy. Don't fool around with a retrofit of your existing sign unless you have a very special sign that can't be replaced easily. If you install a new sign, you will also get a new battery, and you'll remove that item from your maintenance. In addition, the batteries in the LED signs are smaller and cheaper to replace when the time comes.
Q: I've heard about induction lamps. Are they a good technology?
A: Induction lamps are becoming more popular as the price comes down and the technology matures. In the past, they were used mainly in hard-to-reach applications where someone was willing to pay the high first cost to rarely have to go back to the fixture to change the lamp. The upside of induction is that the lamp lasts a long time. 100,000 hours is the claimed life. The downside is that they are expensive as mentioned above, that they experience lumen depreciation of as much as 40% over their lifetime, and that when there is a failure, you need to change the lamp and the ballast (called a generator for induction) at the same time. There are some new induction lamps out that claim to lose only 20% of their rated light output over the 100,000. We have installed induction lamps in parking garages, and they worked well. The light levels weren't as high as the T-8 retrofit we would normally specify, but they were as good as the 175 watt metal halide that they replaced. The retrofit was almost twice as expensive as installing new fluorescent fixtures, but they will not have to perform maintenance on the fixtures for at least ten years. (link to santa clara garage case study)
Q: Do reflectors increase the efficiency of the light fixture?
A: Yes, but not as much as some people would have you believe. Back in the 90's reflector sales people said that a reflector would double the light output of a fixture, and would prove it by taking out four old fluorescent lamps that were losing their light output and installing two new ones with the reflector. They cleaned the lens so more light came through. They got the same light initially, but as the lamps aged and the fixture got dirty they lost light output and customers were unhappy. A good rule of thumb is that a reflector will increase light levels by 25% in a recessed fixture. You have to take into account how efficient the fixture was to begin with. That's not the end of the story, though. When you're replacing T-12 lamps they have probably lost a large percentage of their light output over time. If you're changing to T-8 lamps at the same time that you're installing a reflector you can reduce the energy used because the T-8 lamp will retain more of its initial light output. A T-12 energy saver lamp will lose up to 40% of its initial light output over time. A T-8 "eight series" lamp will lose as little as 10%. This allows us to design for lower initial light levels knowing that we'll maintain more of that light. In many cases, you could just remove one lamp from a three-lamp fixture, install T-8 lamps and an electronic ballast, and achieve the same light levels as you had before. The fixture might also look like a fixture with a missing lamp. That's one of the main reasons I use reflectors. Besides increasing the efficiency of the fixture, they make the fixture look full. A fixture with two lamps and a reflector looks like it was designed for two lamps while a three or four lamp fixture with a lamp removed looks like it. One place where reflectors increase efficiency immensely is in warehouses with dark ceilings and strip fixtures. As much as half the light from the strip fixture goes out the sides or up to the ceiling and is sucked up by the dark wood ceiling. Adding a reflector to the strip fixture increases efficiency of the fixture and improves the distribution of light at the work surface.
Q: The lights on the outside of my building go on and off, seemingly at random. What's happening?
A: Most likely, the outside lights are high pressure sodium (HPS.). They have a copper-yellow color like the street lights. The lamp is going bad, and keeps going out. As it cools down a bit, the igniter starts it again, and it heats up, and goes out again. This is a normal failure mode for HPS. The problem is that if the lamp isn't replaced, the igniter will soon fail and it will cost you more to fix the problem. The answer is to replace the lamp as soon as it starts cycling.
Q: I have metal halide lights in my warehouse and they seem to be a lot dimmer than when they were new. They're also turning pink and blue. Is this normal?
A: Yes, this is normal for metal halide. A normal metal halide lamp will lose as much as 50% of its initial light output over its lifetime, and will experience color shift. The problem is that it is still using as much electricity as it was when it was new. One answer is to replace the lamp when you notice it getting dimmer but before it fails. Another answer is to replace the whole fixture with a fluorescent fixture. In addition to using half the energy to produce the same amount of light as a metal halide, the fluorescent fixture will lose less than 10% of its initial light output over time. PG&E is giving a $100 per fixture rebate for replacing them.
Q: What's the difference between a T-12 and a T-8 lamp?
A: The short answer is that a T-12 is 12/8ths of an inch (1 ½ inch) in diameter, and a T-8 is 8/8ths of an inch (one inch) in diameter. The whole answer is much more complicated than that. A T-8 is generally powered by an electronic ballast which is much more efficient than the magnetic ballast that powers most T-12s. The electronic ballast loses much less energy to heat, and runs the lamp more efficiently. T-8 lamps generally have more types of light producing phosphors in them which contribute to increased energy efficiency, but also improve the light quality. You have probably noticed the greenish tint that objects get under T-12 fluorescents. Because the T-8's have more types of phosphors, they have a more natural color spectrum.
Q: What about T-5 lamps? Are they more efficient than T-8 lamps?
A: All of us in the energy efficiency business were hoping that we could retrofit T-8 to T-5 like we had with T-12 to T-8. It didn't turn out that way. T-5 lamps were slightly more efficient than T-8 lamps when they first came out, but now T-8's are more efficient. The only place I consider T-5 lamps now is when I want a lot of light out of few lamps. There is a T-5 High Output lamp and ballast combination (T-5 HO) that puts out twice the light per lamp as a T-8, but it uses twice the energy to do so. For a while, T-5 HO lamps were great for replacing 400 watt metal halide fixtures in warehouses and gyms, but we have successfully used six lamp T-8 fixtures for the last couple of years. The T-8 fixtures are more efficient, and use the same lamps that are used in the offices, cutting down on one item that needs to be stocked.
Q: I have a tenant who likes to have "full-spectrum" lights in her office. They're very expensive. Are they necessary?
A: T-12 "full spectrum" lamps are often very expensive because they are sold as specialty lights. To measure how "full spectrum" a lamp is look at its color rendering index or CRI. This is measured on a scale of zero to one hundred with zero meaning that you can only discern black and white under that light. One hundred means that you can see colors as well as if you were outside in the sunlight. Older fluorescent lamps have a CRI of 60. Most "full spectrum" lamps have a CRI of 86 to 90. The cheapest T-8 lamps have a CRI of 72. A slightly upgraded T-8 will have a CRI of 86. This meets the definition of "full spectrum" without breaking the bank. The other aspect of the "full spectrum" bulbs is that they often have a bluish or "daylight" color. This has to do with the mix of phosphors in the bulb. Your tenant will be happy with a 6500k (blue color) T-8 with a CRI of 86 and it will cost about one third of what you're paying for the "full spectrum" lamp.
Q: What do all the lamp color notations mean? What's the difference between cool white and 4100K?
A: Cool white is the non-technical way to say 4100K. The Kelvin rating is the color that an object turns when heated to that temperature. (Kelvin is degrees centigrade starting at absolute zero) Warm white corresponds to 3000K. Light white is 3500K. Daylight ranges from 5000K to 6500K.
Q: How many jugglers does it take to change a light bulb?
A: One, but it will require three bulbs.