Flourescent replacements

See, I dont really know what all parameters you include when you say "quality", but I had a meeting with certain vendors few weeks back regarding lighting of plant area and street... and it was concluded that its best to go with conventional fittings in plant areas whereas the primary and secondary streets within the campus can should go with LEDs...
And about the 50,000 hours life: thats actually not very accurate in our case; its comes to somewhat around 35,000. Actually you need to take the ambience into account, assuming all the other parameters remain normal, as per the manufacturers specs...
Hope it helps!!

Hi krahul,

Thanks. Out of interest, what type of fittings and lamps did you go for in the project mentioned and why?

cheers

I am curious to know progress on your project. My understanding is power LEDs (1 w and more) have a declared life of 50,000 hours. but kindly understand some thing not explicitly told to you. For example lumen out put of a very fresh LED is L lumens, it drops down to about 50% of L in just about 7,000 hours. Some LED a manufacturer put it in his power point, others confirmed to me during coffee brake during presentations. Kindly get this from technical people, not jsut marketing chaps. Further LEDs are sensitive to slightest over drive. Ultimately your LEDs will go bad in 5, 000 to 10,000 hours and when you ask LED manufacturer- he will blame driver manufacturer, environment, ambient etc etc.

I will be keen to learn more from your practical experience.

http://www.philipslumileds.com/pdfs/WP12.pdf

Thank you very much for the link to Philips Lumilux LEDs. Will study carefully. Unfortunately many LED manufacturers dot not give this dat and I have personal experience of LED failures - degradation failure due to over drive, & instant failure due to short spikes on DC supply etc.

LED lights are pushed to get high lumens/watt = shortens life. They are also made with insufficient heat sinking = shortens life.

If you create a design that does not push the lumens per watt and has a heat sink made so that dust and fluff will ensure it lasts 100,000 hours, then you can make 100,000 hour LED lamps. They will be a little less bright, but you may not need a socket, they can last the life of the house, as they do now in modern instruments. Of course, they need to be protected from voltage spikes = quick death

I am not yet familiar with the fluorescent tube replacements, so I can't respond to that. I will be anxiously awaiting more info on them. Do you have a link?

Regarding the 50,000 hour lifetime: I have a number of LEDs (red power indicators) that have been glowing with roughly the same brightness 24/7 for about 30 years, which is over 260,000 hours. I also have an LED clock of about the same vintage; most of its LEDs aren't illuminated 24/7, but after roughly 30 years, not one of its 32 or more LEDs has failed. I realize that these put out a lot less light than the white LEDs you are referring to, but they were made using the technology of 30 years ago! 50,000 hours is less than 1/5 of the already proven life of (some) LEDs.

Most white LEDs use phosphors to convert UV and other higher-frequency waves to lower frequencies, so the life of these phosphors might limit the useful life of the units, but it doesn't seem to be the phosphors that fail in fluorescent lamps, so I don't expect phosphors to limit the life of white LEDs either.

If you go to this link it will give you some inforamtion on products available

Lightenup

This is a bit of a side note but Texas Instrument has a really nice cookbook on their offerings in their drivers for LED lighting applications. It provides a lot of answers about "modern" LED supplies.

http://focus.ti.com/lit/sg/slyt349/slyt349.pdf

Thanks for all the various comments. I have been thinking (but not looking very hard) about LED flood lights to replace the 300 watt incandescents in my Church. Apparently not readily available yet from the little I have found; also quite expensive. Plan to check out Phillips.

Before you spend money on LEDs, try finding (reflector) compact fluorescent lights (CFLs). CFLs are always more economical than staying with incandescent bulbs. It is not even worth waiting for the old bulbs to burn out. You may want to increase the number of lamps instead of aiming for a 300 watt equivalent replacement, as the cost goes up with low-volume production models. On the other hand, if you use cool-white CFLs, the increased efficiency may permit a lower lumen rating. Buy a few and see.

If you have to dim the lights, a special dim-able CFL model is required; always more expensive, but usually a controlled-start ballast. Dim-able CFLs also have the virtue of surviving brownouts - the bane of electronic ballasts.

The big issue with fluorescents' is cold starting. If you can find bulbs that start with a short delay, they are likely controlled-start electronic ballasts and may start reliably in cold weather, just more delay and dim at first. These also withstand frequent on/off cycles, and have a longer life in general.

I personally feel its is important to provide surge protection for the branch circuits that CFLs are installed on.

I have been seeing so many comments on how life of LED is affected by over driving etc etc. It struck me that as electronic engineers, we all provide large safety margins of operation when we use transistors, diodes, MOSFETs, thyristors etc etc. If same is applied to operating LED, we should be driving it at nearly 50 to 75% of the current rating mentioned by the manufacturer- in which case the lumen output will be lower, more LEDs will be required for same total lumen output, final cost will go up and everything will be uneconomical. LED manufacturers and marketing people have created a big hype and misleading less technically discerning customers.

Very well summarized the real issue behind LED application - as it stands today. This is the real crux of the matter. I jsut wanted to mention here that I have visited a few LED manufacturers in China. They are actually buying LED dies from US etc and just assembling / oackaging them

in my experience, it could be, as long as the chip was high quality, properly heat sinked, and NOT OVER DRIVEN

don

<...50,000 hour life span...>

5.7 years. Hmmmm.

50,000 hours is quite possible, depending on the quality of the LEDs and any phosphors used. I installed an LED in a doorbell button about 35 years ago. It has been glowing 24 hours a day every day since then, except for the short times it goes out when someone presses the button to announce their arrival. That's well over 300,000 hours of operation.

Of course at that time the only LED color available was red, while this discussion is regarding white LEDs, and today's LEDs can be vastly brighter than was possible back then. That brightness may limit the life of the LEDs. Also, I believe most white LEDs still use phosphors to obtain the white color, so the phosphor may limit the useful life of the unit, as it did on CRT displays.

Street lamps in the Baltimore area have been having issues with the yellow phosphors burning off and displaying a rather purple-ish light.

https://www.aacounty.org/county-council/council-districts/district-5/district-5-blog/are-you-seeing-purple-street-lights