A newsletter reader responds with some thoughtful points about CFLs, reliability, and more
Editor's note: In a recent issue of the Power Management Designline newsletter, I asked about the turn-on/turn-off current of CFLs compared to incandescent bulbs—since the AC-line switch is tested and rated for resistive loads, a non-resistive load may affect switch life. I also linked to a supposedly "helpful" guide to CFLs from the Consumer Federation of America (see here), which I felt was very one-sided and did not admit to any tradeoffs when using non-incandescent bulbs. (You don’t receive the free newsletter? Sign-up details are below.)
A reader, Roger Watkins, provided this insightful response:
"I too have some concerns (as do most informed EE's) with the ban on the incandescents. My concerns are with the lies that have been told to Congress regarding lifetimes of the new technologies (CFL and especially LED), and the significant increase in toxic materials associated with the disposal of these short-lived cheaply made devices.
"Although the lifetime of the LED devices may be rated at 40,000 to 100,000 hours at an appropriate temperature, just like we have all experienced with CFLs, the actual life of the device is generally much shorter due to higher temperature of operation of the device and due to the non-LED components in the assembly. After disassembly of several failed CFL devices and some LED devices, we as a community should understand that the cheap manufacture of such devices will lead to serious pushback and disillusionment of our customers.
"The use of aluminum capacitors in CFL and LED Edison-base devices should be avoided at all costs, and yet it seems that every CFL and LED device I have disassembled, and the photos of every such device I have seen postings of disassembly for, use cheap aluminum capacitors with low temperature ratings. As consumers, most of us are aware that the CFL and LED Edison-base devices fail rapidly in closed fixtures, in outdoor use, in refrigerators, and in oven use.
"The other 'dirty secret' not being discussed much is the dimming with life of LEDs, CFLs, and incandescents as well (as the glass gets tinted by tungsten on an older bulb). The other issue not well understood by non-design types is the change in spectral content from sunlight and incandescent that is associated with LEDs and CFLs.
"Regarding your point on the switch characteristics, generally a 5A resistive -rated switch is rated for about 2A for incandescent loads and about 0.5A for inductive loads, with each specific switch having slightly different ratios. The reason for these large variations are the inductive load has issues with contact separation and stored energy arcing and welding contacts; the incandescent load has a high starting current due to low starting resistance of the filament (similar to capacitive loads but for a different reason); the resistive load has a very nicely behaved characteristic and the only issue is generally contact resistance and self-heating of the switch.
"I am much less worried about the switch failures when converting from incandescents to CFL/LED's because 100W incandescent is generally replaced by less than 30W CFL and by less than 15W LED (with Cree XML or XPG LEDs or similar, again the use of non-specified and overstock cheap LEDs in Chinese manufactured equipment may have a big impact here and lead to even more disillusionment of our customers). If one had a 2A incandescent switch, even an inductive load rating of 0.5A is more than adequate for the 30W CFL.
"Please note that most of the LED schemes will require PFC and such PFC should make the load even less inductive or capacitive in its behavior. I base the 100W equivalent values of CFL and LED lamps on the lumen output of the different types of lamps.
"We are all aware that there is quite a bit of subjectivity here, and that use of non-specified components in the CFL or LED lamp circuitry, especially in the CFL or LED elements themselves, often makes the manufactured lumen output somewhat less than the designed and prototyped lumen output.
"By the way, we both agree on the advocacy issue for the CFA report. As is typical of such a publication, they have accepted the initial brightness figure for the CFL to compute the energy savings, and the 10× figure for bulb life (both unreasonable based on experience). They are spouting nonsense that will give consumers ridiculous expectations on the LED bulbs' lifetimes when consumers are being sold LED assemblies built with cheap aluminum electrolytic capacitors."
Readers: What do you think about this issue, and his comments? ?
Editor's note: Liked this? Want more?
If you are interested in "power" issues such as components; efficiency; thermal concerns; AC/DC and DC/DC supply topologies; batteries; supply ICs; complete supplies; single- and multi-rail management; and supply monitoring: then go to the Power Management Designline home page here for the latest in design, technology, trends, products, and news. Also, sign up for our weekly Power Management Designline Newsletter here.