PITFALLS AND TROUBLESHOOTING ~ Delamping properly
Michael Lane, LC

(text only version ~ for full article with images, please download the complete Lighting Design Lab News, Fall 2001 in Adobe pdf format)

In these days of energy capacity shortage on the West Coast, many businesses are looking for ways to quickly and inexpensively shed electric load. One of the most popular solutions is to take out some of the existing fluorescent light bulbs (properly called lamps). This technique is called "delamping". Delamping of fluorescent luminaires is a possible energy saving solution. There are 2 main questions to ask before delamping any fluorescent luminaire.

1. What will happen to my light level and will this new light level be adequate for the task? The simple answer is that the IESNA (Illuminating Engineering Society of North America) has developed recommended light levels for most lighting tasks. If the delamping does not reduce the light level below these recommended light levels then it is a good idea to delamp.

If the delamping does reduce the light level below recommended levels then productive and worker safety can be compromised. As a rule of thumb for office and schools: Do not delamp the luminaire if doing so will reduce the number of lamps to fewer than two 4-foot lamps for every 64 square feet.

The following is a rough guide and actual light levels will vary depending on reflectance values, partition heights and locations, age of lamps. If upon examination there are 3-lamps lighting 64 square feet then one lamp could be removed without reducing light levels below IESNA recommendations.

If upon examination there are 4-lamps lighting 64 square feet then two lamps could be removed without reducing light levels below IESNA recommendations. Remember, this is a rule of thumb and field conditions (reflectance, room size, dirt) need to be considered.

2. Does it make a difference what kind of ballast I have now?There are series and parallel wired ballasts. Most magnetic ballasts are series wired. It is about 50/50,series to parallel when using electronic ballasts.

With series wired ballasts, when one lamp is removed from the ballast the other lamp will not light properly and will fail if left running. The non-removed lamp will probably not light or will flicker or produce very little light. So, in a series wired ballast we need to remove all of the lamps from the ballast. The ballast will continue to use energy, 3 to 6 watts for magnetic and 0 to 10 watts for electronic. I have heard conflicting reports on delamping series wired electronic ballasts, that this may cause the ballast to fail if left for a prolonged period. I therefore recommend that the power to the ballast be terminated. Magnetic ballasts are very bullet proof and will not fail if left energized, however they will still use some energy.

Parallel wired ballasts can be delamped without too many problems and are often rated by the manufacturer to run one less lamp than the label rating (be sure to check with the manufacturer if the ballast is rated to run fewer lamps than the label states). If you check the ballast list (download ballast list from Lighting Design Lab website in Adobe pdf format), you will notice some 2-lamp ballasts running 1-lamp, 3-lamp ballasts running 2-lamps, and 4-lamp ballasts running 3-lamps, that are rated by the manufacturer to operate properly delamped.

SWITCHING FOR SAVINGS! Controlling light
Randal Smith

(text only version ~ for full article with images, please download the complete Lighting Design Lab News, Fall 2001 in Adobe pdf format)

Should I turn off fluorescent lighting when leaving a room?
Short Answer: Turn them off if you will be gone for more than about 15-20 minutes (for details keep reading).

There are a few misconceptions about fluorescent lighting that keep too many people from turning lights off to save energy. Like many of our myths about energy, there is a small amount of truth in the beliefs.

Misconception # 1: It takes more energy to start a fluorescent that it does to run it, so leave the lights on all the time to save money on your electric bill.

Reality: When you turn on a fluorescent light bulb (correctly called a "lamp"), there is a very brief jump in current when the ballast charges the cathodes and causes the lamp to start. This inrush of current can be many times greater than the normal operating current of the lamp. However, the spike of current draw normally lasts no longer than 1/10th of a second, and draws the equivalent of about 5 seconds of normal operation. So, if you turn your fluorescent lamp off and on more frequently than every 5 seconds, you will use more power than normal. So, normal switching of fluorescent lamps has very, very, very little effect on a power bill.

Misconception #2: Turning fluorescent lamps off and on wears them out right away. Reality: Electric lights have a published rating for expected life. The rating is in the thousands of hours for fluorescents. Fluorescent lights have a life rating based on how many hours they are left on every time they are turned on. This is usually referred to as "burn time" for fluorescent lights the burn time is three hours. Every time a fluorescent light is turned on, a tiny amount of the coating on the electrodes is burned off. Eventually, enough coating is burned off, and the lamp fails to start. Most full-size fluorescent lamps are rated to last 20,000 hours when left on for 3 hours every time they are turned on. This means that the lamp has roughly 6,667 starts available to use up. (20,000/3 = 6,667)

Longer burns extend lamp life. If you "burn" your fluorescent lamps shorter than 3 hours per start, you use up your potential starts faster. If you "burn" them longer than 3 hours per start, you use up your starts more slowly. However, you are paying energy costs for the operating time of the lamps, and the most efficient lamp is the one that is not on when it is not needed.

But longer burns use more energy. Operating a light when it is not needed is simply spending money for no purpose. Today's rapidly rising electric rates mandate that every building becomes leaner with energy use to control costs.

Find the trade off point. There is a point where the amount of money you save from turning off the light exceeds the cost of reducing lamp life by more frequent starts. If you use the formula in Table 1 at $0.05 KWh, you come up with a time of about 15 to 20 minutes for that point. As energy rates go higher, that time becomes shorter. If you pay less than a nickel per kilowatt hour, your turning-off point would be longer.

Ballast types are important. The kind of ballast you use may make a difference if you turn your fluorescent lights off frequently. There are three different kinds of electronic ballasts: instant start; rapid start; and programmed start. Which one you use can influence your choice of how frequently to switch off your fluorescent lights.

Download the complete Lighting Design Lab News, Fall 2001 in Adobe pdf format.