LEDs as lamp replacements

Points well taken, but I'm gonna reserve judgement at this time, until I can find out how it's done. If the whole string of LEDs is in series, and they are not super high power types requiring an amp continuous, then we could be talking just 150mA or so. Alternatively, we could be talking pulsing the whole string at an amp or so. I really think that I'm going to have to buy one, and attack it with the Dremmel ... I can't think that I have ever seen any kind of switching supply that works from low frequency AC input power, that doesn't have a smoothing cap. It's hard to see how it could be done without, unless you employ 'electronic' smoothing using a regulator with feedback, as I have sometimes seen done in 'professional' equipment, but even then, you're going to be talking circuitry that is as big as a smoothing cap of as little as 22uF at the required 400v working, would be.

Looking at the pictures of the Cree GU10 replacements, it's hard to say if the enclosure is a 100% ringer for the incandescent version, but even if it's not, it still looks pretty tight to get any kind of 'conventional' switcher squeezed into.

Arfa

"Arfa Daily" wrote in news:WUsli.14837$ snipped-for-privacy@newsfe2-win.ntli.net:

Set to with zeal, my son. >:) If I had a dremel, I would. Probably.

Did find this though:

That's interesting because it shows >90% efficiency as I hoped might be had, from a circuit with no large smoothing capacitor. It's just one tiny IC driving a MOSFET and using an inductor. I don't know how big that inductor is, but not very, I imagine. Maybe similar to the one on the module on the eBay page I linked to earlier. A series chain of three or four LED's might well be driven directly from the mains, and all fitted inside one of those small lamp capsules. Heat dispersal might be tight, but doable, especially in those lamps with the fine louvre shells to allow convection to get in amongst the doings.

There might need to be some amount of filtering done on the input that is not shown on the sample schematic. The chip needs a minimum of 8 VDC input, so to for an AC bulb replacement, you'd need to add a bridge rectifier and probably a small filtering cap.

Well, that's not strictly true. The issue of where the input voltage comes from, is carefully avoided in the data sheet. It only shows that the chip can operate from a DC input range of 8 to 450v. To get the DC input from the mains, would still require a bridge and smoothing cap. However, looks like a useful chip, and a good candidate for the back end processing. It claims that it can drive "hundreds" of LEDs in series / parallel strings. Still reserving judgement at this time ...

Arfa

Here's a really interesting site

Follow the various page links to the chromaticity chart, and " More information on LEDs" at the bottom. I didn't realise that they were already in use in street lighting. There is mention of higher colour temperatures improving human night vision. There is also an interesting LED colour chart, which shows one at 4500K called "incandescent". A couple of years back, I was in Disney when they put on a show in front of the Magic Castle. There was a stage spot set up on the top of a pole, projecting a brilliant white beam of considerable strength. I didn't take much notice of it, until it suddenly changed colour. During the show, it produced a whole range of colours, but I couldn't see that the enclosure was anything like big enough to accommodate a coloured gel wheel. I remember wondering at the time, if this had been implemented using very high power RGB LEDs. I suppose that it is also possible that it could have been a plasma lamp with dichroic mirrors and LCD panels. Are any LEDs actually powerful enough to make stage lighting from ? Can they be mounted in any way that allows light collection and direction through beam forming optics ?

Arfa

LED's are being used for stage lighting, but not in the high power movers or Ellipsoid's (YET). WHat you probably saw was a martin MAC2000 or such at disney. They have full color mixing onboard VIA DMX

THere are some interesting new LED stage lighting also:

BOB

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BOB

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It didn't look quite like that and didn't have remote move capabilities, but was remotely controlled in as much as the colour changing and intensity, so I guess it was on a DMX bus. It was on the top of a pole, so clearly made to work in outdoor conditions, and small and squat, which was made me think that it used technology that I hadn't seen in that application before. I also seem to recall that I was particularly struck by the range and intensity of the colours it produced. Guess I'll never know for sure. The links contained some interesting stuff on high power LED lighting. Seems to me that the LEDs themselves have pretty much evolved to the point of usefulness, and that it now needs more developments in the optical part of the equation, and colour temperature rendition. BTW, did you get the partial schematic for the 'HT70 that I sent you, as requested in your post of a few days ago ?

Arfa

"Arfa Daily" wrote in news:7hzli.8397$ snipped-for-privacy@newsfe4-win.ntli.net:

Hmm. :) Last post after a long day, that was. Should have seen that it needed DC.

No, i did not get it. could you resend it? Email has been funky lateley......

Bob

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OK, it's resent to the same address that you used to post this, but from a different one of my addresses. Attachment is a 434k PDF, which shouldn't be a problem. Let me know that you get it ok. If any issues, just contact me direct on the arfa daily address that I use to post here.

Arfa

Got this one. thanks.

Bob

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