They why does my employer change out the fluorescent lighting about every 5 or 6 years even when they are all burning good? When they do, the rooms are so much brighter. Makes a huge difference.
ALL lighting dims with use! It is called "Lamp Lumen Depreciation" (LLD) by the pros and can be found in the detailed specifications from the manufacturers. Mostly in fluorescents the electrode loses some tungsten (those black ends, just like incandescents) and there is some mercury loss as well. Both degrade the starting and the arc, THAT causes less light.
Electronics is a whole other issue. As is dirt on the bulb and fixture.
It is useful to note that LLD is not related to when a lamp fails. This is why some folks claim bulbs that have lasted extreme times, the efficiency has gone to ****.
Other things to note:
Formula is as follows: (Lumens (adjusted for LLD if you want get detailed) x Life) / (Watts x Life x $) = true efficiency (lumens per dollar). Note that you have to get your units right. Power is usually sold in KWH = 1000 watts for one hour or one watt for 1000 hours. Also the lamp life is an average statistic so it applies over large numbers of bulbs. ;-)
- colored - 130V -120V - "long life" - halogen - shatter resistant - vibration resistant.... ALL have different light output.
Richard Reid, LC Luminous Views Lighting Design for Home and Business
Yes, they do, in fact their lifetime is based not on loss of functionality, but on reaching some percentage of nominal output.
No, that would make relative efficiency _drop_ over time.
But perhaps no more accurately. I've seen Bunsen photometers in modern physics labs, mounted on optical benches, and so on.
Nick
I'm betting the replacement was wasted. That's because the lamps were changes individually as they failed. In other words, the average age of the tubes they were changing out was far less than 5 years!
I have 14ea 48" tubes in my home, shop, and garage, and I'll bet the average age is less than 2 years.
Excellent experiment.
Have you ever done a long term cost analysis on CF vs. incandescent? Does the increased cost and short life of CF's negate the improved efficiency?
Thanks!
No, that is the reason to change out all the bulbs. At home we usually change a bulb when it is gone. No big deal. In a factory or large office, getting the lifts, scaffolding or whatever together, two employees + overhead costs, they often find it cheaper just to sweep through an area and change 100% of the bulbs at one time. That way, there are few, if any, changes between, thus the average is still very high at 5 years.
If one bulb goes, all the others at that age are probably not far behind. At work, we don't change the entire plant, but will do a section at a time. When you have 20' ceilings, it is cheaper to change what you can get at once the equipment is in place.
What short lives? I've been writing the install date on my CFs from the beginning and have been keeping a log. Average life is about 4.5 years. The best one, a low wattage lamp in my bathroom that burns
24/7 is still going at 9+ years.When I can buy a pack of 5 from Sam's for $9, only a bit more than an equivalent incandescent, the enconomics become a no-brainer.
John
Agreed. The use of 'group relamping' (replacing all bulbs at once even though many are still burning) has some advantages even though some bulbs are replaced prematurely. Since bulb life is pretty predictable, most of the replacements will not burn out too soon. All the bulbs are from the same stock (usually), so it avoids mixing up different 'colors' such as 'cool white', 'softwhite' and 'daylight' in an area. And as you mentioned, the 'overhead' of getting crew, tools, and equipment scheduled. If 'group relamping' is done on a performance basis (for example, whenever 10% of the bulbs have burned out), then large areas of burned out bulbs are usually avoided.
'Spot relamping' has the advantage that maximum use of each bulb is attained and only a small quantity of replacements are needed to keep on hand at any one time.daestrom
Problem with your Bunsen photometer, Nick, is that it only compares a very narrow cone of light from each source. Needless to say, CF's come in all shapes. The light emitted in one particular direction of one tube shape is
*not* the end all total story.To make a better measurement, you would need to roll/pitch/yaw the test bulb in all sorts of positions to measure the output in each direction. Or build a test box with the interior surface lined with photometers.
Just comparing a typical incandescent (more or less globular) output with a CF with a different shape is subject to these sorts of errors.
daestrom
It is NOT out of the ordinary in commercial and institutional use, for QUALITY tubes to last more than 3 years, and changing en mass before failure is standard maintenance procedure. If maintenance needs to change more than a few tubes before scheduled change-out, they either modify the changeout schedule or find a new supplier!!!!!!!
5 years MIGHT be stretching it, but I know on office where in the last 5 years only 2 or 3 bulbs had been replaced (along with about 4 ballasts) before a mass relamping and reballasting took place.
I use Sylvania and GE, and sometimes they go out within a month. I do have 1 good CF that must be 7-8 years old, but most don't last a year.
What brands could you recommend that last longer than Sylvania and GE?
19 (if I counted right) 12W CFs here for over 7 years. One failure so far at about 6 years.
Wayne
I suppose this problem diminishes with distance. A white paper reflector behind each bulb might help.
Nick
Do you live in a rural area? Is it possible that your power has severe fluctuations? Frequent lightning strikes? Unfortunately, rural power isn't as clean as urban (as a crude generalization). That could contribute to your short bulb life.
I use Phillips and 'Globe Energy Savers' (a brand in a big box hardware store) and get years out of them. I'd say 4-5 years is typical for me and some last longer.
Mike
The new fluorescent bulbs have a higher color temperature with more blue light causing the perception of being much brighter.
I think more likely the phosphor degrades as the bulbs are used and the replacement ones simply have full brightness.
There are many 4-foot fluorescent lamps now rated to last 20,000 or
24,000 hours, and that is with 3 operating hours per start. Expect a bit more with one start per workday.This means to me expect half to burn out in 5.5-6.5 years if used 10 hours a day 5 days a week and lasting no longer at 10 hours per start than at 3 hours per start. Some installations will experience worse and some will experience better.
Meanwhile, light output will decrease over the life of a fluorescent lamp. It appears to me that a 32 watt T8 (1 inch diameter 4-footer) is rated to be typically down about 5% in light output when 40% of the way through its rated life, and I would expect about 10% down when getting close to rated life. And it appears to me that typical phosphor degradation is about double that for T12 (34 and 40 watt 1.5 inch diameter) with older-tech phosphors. I have known low-mercury ones to sometimes degrade faster due to the mercury supply getting stuck in parts of the bulb from chemical reactions and/or maybe mercury ions getting embedded into whatever, maybe in the phosphor.
- Don Klipstein ( snipped-for-privacy@misty.com)
I don't care about "perception of being brighter", I just know that when they do get changed out, you damn near have to wear sunglasses because it is so bright.
While this may be true in some cases, going from 2700K to 3100K to 3500K or maybe even to 4100K can happen, but is unlikely.
They buy several cases of bulbs from the same supplier that they have always dealt with, almost always buying the same bulb every time. The bulbs do dim with age, and may be down to 50% of initial light output just before failure. At 5-6 years of age on the lamps, on 12 or more hours a day 5-7 days a week, light output may be down to 60-70% of initial output.
So replacing Cool White lamps with new Cool White lamps WILL provide a noticeable difference in overall lighting levels when a large area of them that are 5-6 years old are replaced.
Any CFL brand that is Energy Star listed has to have lamp life tested and the data supplied to Energy Star periodically to keep the listing. Energy Star requires testing of other performance data too. See:
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