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Old 04-12-2010, 06:48   #76
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Jon,
Well said and I stand corrected on the chip ID I stated...it should be a SMD5050. Did you look at the 24 segment chip G4-LC with the #3528 diode, rated at 150 lumens? It is rated at 1.9 watts vs 2.5 for the G4-LT. It is also slightly smaller. I need the slightly smaller size for use in certain applications but am concerned about the quality of light.
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Old 04-12-2010, 18:02   #77
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Originally Posted by Dynamo1181 View Post
Jon, Did you look at the 24 segment chip G4-LC with the #3528 diode, rated at 150 lumens? It is rated at 1.9 watts vs 2.5 for the G4-LT. It is also slightly smaller. I need the slightly smaller size for use in certain applications but am concerned about the quality of light. A
Hi Alan - I saw that unit but didn't try any of them. I also didn't notice its light or power rating. I guess now that I know the SMD5050, I couldn't afford to try other LED segments. We're cruising along the coast of Malaysia, so getting stuff sent to us is difficult. I can really only do minimal experimentation. The SMD5050 looks good & works well & seems to be used by lots of different companies. But I'd be interested in hearing if something better comes along.

I also haven't checked out the single-chip "high-power" LEDs that typically draw a full 1W or so by themselves. I've seen some & they seem bright, but I don't have a real, factual comparison of light output or current input between the high-power LEDs & the SMD5050 (or any others, for that matter). I wish someone would publish such a comparison - it would make our selection job much easier.
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Old 13-12-2010, 06:43   #78
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Just found sensibulb on ebay Sensibulb LED replacement bulb - eBay (item 320551046936 end time Dec-16-10 08:06:19 PST)

That said I just purchased 10 if these http://cgi.ebay.com/ebaymotors/ws/eB...ht_3077wt_1172



They are the same as the last ones I purchased but they already have the right base and are about 4.8W I had to change the bases on the last ones. But they worked great. No need to spend up big on expensive LEDs, but I have inquired about shipping to AU for the sensibulbs just to compare.
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Old 13-12-2010, 07:31   #79
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Dennisail - if the bulb module you show is really burning 5 watts I would be concerned about longevity. With LEDs, it is all about waste heat dissipation, and in a form factor that small I think the module will get extremely hot and not last long. A rule of thumb has been about one square inch of heat sink in free air per watt for good performance and lifetime. If you aren't seeking tens of thousands of hours to half brightness you can certainly push that guide a bit, but not a whole lot.

Moving air, and the fixture socket itself will help with all this, but 5 watts is still a lot of heat to deal with.

Chip
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Old 13-12-2010, 07:51   #80
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In practice they get warm, not hot. I measured 4.6W on the last ones, but that includes the internal resistor. They are hollow so have good air circulation and for $4 you just throw it away and put a new one in. I estimate they would have close to 5 square inch of surface area anyway when you include the insides.
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Old 13-12-2010, 18:56   #81
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I just emailed these guys Bo Ya Lighting(HK)Co., Ltd -dimmable led bulb,SMD led lamp,G4 led light
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Old 13-12-2010, 22:08   #82
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Also does anyone know what the higher power LEDs are called and where you can get them cheap? I mean if they can sell a whole 5W headlamp and ship it internationality for $8 surely the LED's they are using must be very cheap. I would love to get a few 1-5W LEDs to make a few lights with. The sensibulbs only appear to have 2 x 1W units on them.
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Old 13-12-2010, 22:57   #83
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It would be nice if we could move from talking about power consumed (watts) to light output (lumens, or something similar). Yes, power consumed is important, but light output is probably the more relevant number initially, as there are LOTS of LEDs that don't put out much light. With LEDs, there's no easy relationship between power & light, as there is with most incandescents.

In fact, it would be really useful if someone could come up with a table showing the light output, nominal voltage, & current consumed for various LEDs. Anyone know if there's a table like this around? Or anyone want to put one together & share it?
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Old 14-12-2010, 01:13   #84
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Power input is easily measured. Light output isn't. Power may not be as linear as an incandescent lamp but its still a good measure. A single focused high output LED beaming straight into a lux meter will give a higher reading than multiple LEDs producing more actual light but shining it multiple directions. In my testing so far I have found the real world relationship between current and visible light output fairly consistent.
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Old 14-12-2010, 03:34   #85
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G'day Dennis. I agree that light output is difficult to measure, for the reasons you point out. A relative measure might be possible with a good camera, but I was hoping for more precision than that.

Perhaps the LEDs that you have looked at have a fairly linear power/light relationship. But that's certainly not what I've found in my research. Just assuming that an LED that draws 2x the current will be twice as bright is asking for dissappointment, IMHO. I suspect that the 1W+ LEDs have a very different power/light relationship from the lower power LEDs like the 5050. They're very different LEDs.

The voltage is also an issue if you're buildiing up your own. If the actual LED wants, say, 5v, then you might get away with running 2 in series & running the same current through each. With a 3v LED, you can stack 3 in series. But a 6v LED is a problem. There might not be enough voltage left after stacking 2 in series to run a constant current source without fairly significant wastage. And running just 1 from a 12v source means dropping a lot of current (& 6+v) in your regulator circuit, which is pure wastage, or building a DC-DC converter, which gets into RF & complication issues.
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Old 14-12-2010, 04:52   #86
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It would be nice if we could move from talking about power consumed (watts) to light output (lumens, or something similar)...
Lighting engineers use “Luminous Efficacy” , which is the ratio between the total luminous flux (lumens) emitted by a source and the total amount of input power (Watts) it consumes - hence, lumens per watt (lm/W).

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Solid-State Lighting: Luminous Efficacy
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Old 14-12-2010, 06:46   #87
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Thumbs up Luminous Efficacy

Gord - Thank you for that link! Great info. Lumens/Watt is exactly what I'm looking for.

Some of it's a bit dated (most pages seem to be c. 2007) but the science is explained well. Nice to see the DOE taking LEDs seriously. They also show why it's so difficult to measure & compare LED lighting systems. But at least they're thinking about comparisons, as we really need a good comparison mechanism to decide what we want to buy.

Interesting that they show warm-white LEDs as 25-44 lm/W (as of 2007). Our warm-white 10-segment SMD5050 G4 replacements are putting out ~120 lumens at a cost of <2W, so at least 60 lm/W (& probably closer to 100 lm/W). Nice to see technology moving ahead so quickly. We've already improved by a factor of 2-3 in only 3 years, almost as fast as Moore's Law. Doubling that in the next 15 years to their goal of 160 lm/W by 2025 should be easy.
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Old 14-12-2010, 06:54   #88
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The highest performing high power LEDs right now are the Cree XM-L series, which put out about 290 lumens at a drive current of 700 mA and a forward voltage of about 3.0. That is about 140 lumens/watt, compared to the best quartz halogen bulbs that give 24 lumens per watt, and fluorescents which peak out at nearly 100 lumens/watt. These LEDs will also take much higher drive currents (with proper heat sinking of course) for even more light output but at falling efficiencies.

LEDs do not have a linear light output to power input ratio. Light output falls more slowly than power input, giving higher efficiency per watt. If you look at input voltage, the graph changes. As voltage applied to an LED falls, current through it, power consumed, and light output fall even more rapidly. Conversely, small increases in voltage can result in large increases in power consumed, and in waste heat generated. As an LED heats up, the forward voltage across it falls, and it draws even more current. If current isn't somehow limited, the LED can go into thermal runaway and self destruct. Thats one reason heat management, and current limiting in some form, are so important with LEDs.
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Old 14-12-2010, 06:56   #89
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Jon,
In ordering from BO YA, did you get the warm, pure or cool white LEDs? It appears the the warm LEDs have about 35% less output than the cool white units. I would assume the bright white units(4000-500K) would fall in between.
BTW I am dealing with Jessie there, who I find most helpful.
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Old 14-12-2010, 07:03   #90
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As a point of interest, the maximum theoretical efficiency of an LED is about 640 lumens per watt. This would be pure green light, since the eye is most sensitive to this color and lumens are based on light perception. The maximum theoretical efficiency of a white LED is in the range of 250 lumens per watt. I don't remember the exact number, but that give you an idea of the upper limit of white light production efficiency. As white LEDs continue to improve in efficiency, the improvements are going to come in smaller and smaller steps.
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