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Old 25th November 2012, 12:56 PM   #191
AndrewT is offline AndrewT  Scotland
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Default dx.com

like theseCould the aluminium PCB be cut into 4 strips? each with 7LEDs @ 24V and ~300mA for maximum of 7W input?
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Last edited by AndrewT; 25th November 2012 at 01:04 PM.
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Old 25th November 2012, 01:05 PM   #192
freax is offline freax  Australia
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Originally Posted by AndrewT View Post
like these

Could the aluminium PCB be cut into 4 strips? each with 7LEDs @ 24V and ~300mA for maximum of 7W input?
Why bother? just buy a strip:

High Power 16W 950LM LED Emitter Metal Strip (12~14V) - Worldwide Free Shipping - DX

There are many many other kinds on there just search for "led strip diy"
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Old 25th November 2012, 01:10 PM   #193
Pano is offline Pano  United States
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Originally Posted by tvrgeek View Post
o go off the deep end, look up Red Light District tube amp and you will see what a few hundred can do.
LOL. Did you just tell SY to look up the Red Light District amp? Or was that for the rest of us?

The Red Light District: A 15W Push-Pull Amplifier
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Old 25th November 2012, 01:44 PM   #194
freax is offline freax  Australia
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It should be noted that I did buy a LED night light today so I can stop having to turn on the light every time I need to get up to take a leak, and I rather loved the colour output of it and brightness of it too:

The colour shown is accurate, it looks like the closest candidate to incandescent that I've seen so far, picture was taken with an ipad 3.
Click the image to open in full size.
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Old 25th November 2012, 01:57 PM   #195
djQUAN is offline djQUAN  Philippines
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Quote:
Originally Posted by freax View Post
dx.com has some nice LED strips that I've been meaning to try out, they also have some great WF-501B knockoffs, charging the required batteries can be a bit tricky/explosive though, haha.

TK Monster Explosion

As you say, buying quality is of the upmost importance to me too, same goes with rechargeable Li-ion batteries.



In summary, if a battery can do this:


If you wanna get into LED flashlights and their associated batteries, you'd be best to buy good quality.
So far I've been lucky with Li-ION batteries. I often measure cheapie chargers if they are within spec (most aren't) and get modified or junked if they exceed the 4.2V open circuit spec. These days, I buy AA powered lights as they are far more practical as you can buy AAs everywhere. No need for specialized batteries.
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Old 25th November 2012, 02:03 PM   #196
freax is offline freax  Australia
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Indeed, I've standardized myself on AA aswell, its got the best balance of weight/power density/size. You can get dual chemistry flashlights on dx, ones that will run fine on 1.2v NiMH or 14500 Li-Ion rechargables.

Though for my bhi DSP project I've used 2x 14500's in series inorder to create the required 8.4v nominal to power 3x devices at the same time but also manage to not go outside of specifications on any of them, one has a voltage limit of 9v, the other 12v, etc. The lifetime per charge is also exceptionally long. For small projects, Li-Ion rechargeable just can't be beat for size/weight/power density Vs NiMH...

The project uses 2x FM receiver modules + 1x bhi DSP board + 1x LM386 amplifier board.

It receives audio from a radio receiver via a cheap FM transmitter dongle that I bought off ebay on 87mhz, it receives this transmission through one of either the two FM receiver modules (switchable between), then the output of the FM receiver module is fed directly into the bhi DSP board, then the output of the bhi DSP board goes to the LM386, and the LM386 is set at a low gain that then goes to a mono headphone output.

I wish C was more popular than it is though.

D is pretty much useless nowdays. Though I still have a Duracell Dolphin light hanging around that takes lantern batteries, you just can't beat a nice big reflector and an incandescent globe sometimes, that and its waterproof and cheap.
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Last edited by freax; 25th November 2012 at 02:11 PM.
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Old 25th November 2012, 03:24 PM   #197
jitter is offline jitter  Netherlands
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Originally Posted by tvrgeek View Post
#187, 188 I am pretty sure, for an LED lamp half life is not MBTF.(mean time between failure)
MTBF is not the expected lifetime, but the average time between first failure and second failure of a system. See this wiki.

Quote:
Just like a florescent bulb, It is the average time until the light emitted has degraded to some specific level. Florescent are spec to 80% I think.
No, this is lumen depreciation, the opposite (how much light is left) is lumen maintenance.

As an example here's a link to the specifications of a simple low pressure sodium lamp. Among the specs are the expected lifetime at failure rates of 5%, 20% and 50% and the lumen maintenance at 2,000 and 5,000 hours.
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Old 25th November 2012, 11:32 PM   #198
Pano is offline Pano  United States
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The colour shown is accurate, it looks like the closest candidate to incandescent that I've seen so far,....
They seem to be getting better. I've seen strings of white LED Christmas lights that were a cold white and others, seemingly identical when off, that looked incandescent when powered. So much so, I had to look very closely to believe they were not "real" Christmas lights.
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Old 29th November 2012, 04:57 PM   #199
rsavas is offline rsavas  Canada
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Default LED Standardization

Hello folks,

Well today I was asked at work to do some LED research and low and behold there is some LED standardization going on.
http://www.zhagastandard.org
Of course, it looks like Philips is behind this, along with many other large and some smaller OEM's but it shows that these folks are starting to address this very important issue with regard to this technology.
Also found this, as well
LED street light / road light fixtures using LED light modules by Philips Lighting
LED mfg's & the consortium have standardized hours until lumen depreciation meets 70% of initial
BTW a F54T5HO lamp depreciates to ~95% over its life span,~20-30khr, a huge difference in performance, this is why they are the #1 lamp used today for high-bay applications, lets see how long it takes for an LED to displace this technology.
Regards
Rick

Last edited by rsavas; 29th November 2012 at 05:05 PM.
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Old 1st December 2012, 05:16 PM   #200
jitter is offline jitter  Netherlands
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Originally Posted by rsavas View Post
Hello folks,

Well today I was asked at work to do some LED research and low and behold there is some LED standardization going on.
http://www.zhagastandard.org
Of course, it looks like Philips is behind this, along with many other large and some smaller OEM's but it shows that these folks are starting to address this very important issue with regard to this technology.
I stand corrected, apparently the manufacturers do see the advantage of standardization after all. I still doubt that this will be the case for consumer LED lighting products, but who knows...

Could you check this link? It doesn't seem to work.

Quote:
LED mfg's & the consortium have standardized hours until lumen depreciation meets 70% of initial
A logical choice as "The appropriate lumen maintenance target is usually based on the application and the requirements set forth by customers. Since the human eye generally can’t detect a change in light output until there has been 30% depreciation, L70 is often established as the target for an application." (source).
Also "CFLs produce less light later in their lives than when they are new. The light output decay is exponential, with the fastest losses being soon after the lamp is first used. By the end of their lives, CFLs can be expected to produce 70–80% of their original light output. The response of the human eye to light is logarithmic. One photographic "f-stop" reduction represents a halving in actual light, but is subjectively quite a small change. A 20–30% reduction over many thousands of hours represents a change of about half an f-stop. So, presuming the illumination provided by the lamp was ample at the beginning of its life, such a difference will be compensated for by the eyes." (source)

Quote:
BTW a F54T5HO lamp depreciates to ~95% over its life span,~20-30khr, a huge difference in performance, this is why they are the #1 lamp used today for high-bay applications, lets see how long it takes for an LED to displace this technology.
That might be shorter than you think. Granted, for existing installations the most economical solution (for now) would be to replace the lamps when they're nearing end of life rather than replace the luminaires by new ones. When it comes to new installations or renovation, then perhaps the choice for LED luminaires is more easily made, especially if the price has dropped some more.
Those F54T5HO (or TL5 HO, 54W as I know them) have a lamp luminous efficacy of about 90 lm/W. Luminaire efficacy will be lower than this because of the losses in the ballast and optical losses in the luminaire.
Here's an example of a LED highbay luminaire with a luminaire luminous efficacy of 82 - 91 lm/W (depending on the version). The lumen maintenance after 40,000 hours is still 90%, when you're already through most of the life of the second set of F54T5HOs.

To adress lumen depreciation, I've read of luminaires equipped with "CLO", i.e. constant light output. End-of-life output is treated as target light output and new light sources are dimmed to that level, in the process power consumption is also lowered. Then, as the source ages, dimming is gradually lowered to keep the light output at the desired level.
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