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Thread: Strobes: Xenon vs LED

  1. #41
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    Thanks. Done...

    Incidentally, I don't know if there is much disassociation between colour temperature and actual spectrum, but I guess there could be, just as there are many mixes of three wavelengths that will get white. It may be that this, if relevant, is why filter gels failed to get the effects I hoped they might.

  2. #42
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    Quote Originally Posted by mixedgas View Post
    The pulse rating is there, but it does not gain you much higher average brightness. If the die is hot, on phosphor based leds, the pump wavelength shifts
    far enough to defeat the extra energy. This has been debated on electrical engineering forums for years. The consensus was, on a few early leds, there was a net gain in average output power when pulsing. Later devices did not exhibit the effect, and the myth persisted.
    Still correct, if the die is hot the extra energy goes to waste... but LEDs nowadays are efficient enough that they don't get hot enough for that to happen when pulsed. I've had good results in 2x the drive current with Cree XM-L2s (6A instead of 3A). They can even survive being driven CW if the thermal interface is good enough (direct metal contact under the led heatsink pad- no prepreg.) After you bring up the current too much, though, you get a problem of blowing bond wires.

    Quote Originally Posted by mixedgas View Post
    Tests in pulsing Luxeons, up to Luxeon III or IV showed that they were fast, a turn-on time about ~100 nS, but brightness was not significantly enhanced. I used to design for a LED flashlight company. I had access to Nichia and Luxeon of a very good binning.
    Turn on time is still fast. Luxeon III/Vs were succeeded by the Luxeon K2, then Rebel, K2 TFFC, Rebel TFFC. in the middle of the K2 and Rebel business Cree surpassed Philips efficacy wise, with release of their XR-E, MC-E, XP-E, XP-G, XM-L, XP-G2, XM-L2.. too many to keep track of (lots in between, but I'm only writing down some of the more notable ones. There are a ton of other packages with multiple dies.

    Quote Originally Posted by The_Doctor View Post
    Incidentally, I don't know if there is much disassociation between colour temperature and actual spectrum, but I guess there could be, just as there are many mixes of three wavelengths that will get white. It may be that this, if relevant, is why filter gels failed to get the effects I hoped they might.
    There is indeed disassociation between colour temp and spectrum. You'd be thinking of colour rendering (CRI) http://en.wikipedia.org/wiki/Color_rendering_index
    It's not a perfect rating(by any means) but for now, it'll do until everyone agrees on a new standard.
    Cree started naming the colour temperatures.. Warm White 2600 - 3700K, Outdoor White 3500 - 5300K, Neutral White 3700 - 5000K, Cool White 5000 - 8300K
    Incandescent bulbs are generally warm white, fluorescent tubes are usually cool white. Warm white is generally more yellow/orange, and cool white is more blue.

    Everyone has different preferences though, it's best you first dig up a specific colour temperature, then try to get the best CRI you can, either by mixing multiple LEDs (White LEDs are notoriously low in reds/ambers), or purchasing high CRI emitters. Nichia is good for high CRI emitters. Cree is good for best efficacy (they're working on colour, too, look up the Cree LED bulb. They're dirt cheap and an excellent value for the price- USA only, IIRC). Luxeon? They seem to be focusing on emitters for the automotive market.

    As for replacing the array in your light - what kind of driver is in there?

    Hope this helps.


    Craig

  3. #43
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    Anyway, if I can redirect the thread back to strobes, a bit, I was wondering if anyone was using these:

    http://www.thomann.de/gb/american_dj_freq_16_strobe.htm

    or the 5 LED version.

  4. #44
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    Sorry White-Light, unavoidably off-topic now, but at least it helps keep the thread up in the activity list..

    Quote Originally Posted by csshih View Post
    There is indeed disassociation between colour temp and spectrum. You'd be thinking of colour rendering (CRI) http://en.wikipedia.org/wiki/Color_rendering_index
    It's not a perfect rating(by any means) but for now, it'll do until everyone agrees on a new standard.
    Cree started naming the colour temperatures.. Warm White 2600 - 3700K, Outdoor White 3500 - 5300K, Neutral White 3700 - 5000K, Cool White 5000 - 8300K
    Incandescent bulbs are generally warm white, fluorescent tubes are usually cool white. Warm white is generally more yellow/orange, and cool white is more blue.

    Everyone has different preferences though, it's best you first dig up a specific colour temperature, then try to get the best CRI you can, either by mixing multiple LEDs (White LEDs are notoriously low in reds/ambers), or purchasing high CRI emitters. Nichia is good for high CRI emitters. Cree is good for best efficacy (they're working on colour, too, look up the Cree LED bulb. They're dirt cheap and an excellent value for the price- USA only, IIRC). Luxeon? They seem to be focusing on emitters for the automotive market.

    As for replacing the array in your light - what kind of driver is in there?
    Thanks for posting. The driver is a 37V current limited DC output supply that came with it, and also a thing I devised based on an LM317 for linear dimming, duped into wanting 0.25V across its sense resistor instead of 1.25V, reducing total voltage drop and saving power. The array Vf is about 32V and the open-circuit supply output tops out at 36.6V, more than enough difference to allow insertion of my dimmer. While I designed it for a 12V LED floodlight with grounded cathode, I was able to adapt it successfully to this high power lamp because the LED array is not electrically connected to its baseplate at either end, so a couple of low power zener diodes were used to manipulate grounds for op-amps to allow the regulator to handle the large LED Vf. So long as the replacement LED is about 32Vf and isolated from its baseplate, and has an emitter area of 7/8'' squared I can use it.

    It's actually a 30W lamp fitted with a 50W LED, but I rarely use it at full power. Even when I do, I find that the heat is modest (ambient tenmperature never gets very hot here so I risked it), there's no significant shift in colour like I often see in LED flashlights with different power. The seller's original LED options were cool white and warm white. (3500K, I forget what the cool white temperature was, and can't find my records of buying it). The mixed-phosphor one was intended to balance the two but the resultant colour is horrible, so instead of trying to correct it (suggestions and requests to the maker failed, as have filter gels), I'm going on the basis of hopeful recognition of familiar LED's. The Luxeon Rebel RB100 used in a Fenix P3D 'premium' flashlight is as good as I have ever seen. I'd settle for 50 watts of that! So long as it came on a physically and electrically compatible baseplate for the big lamp...


    It could be worth mentioning here that my dimmer can be modulated. Fast. Might be useful in a high power DIY strobe...

  5. #45
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    Talking of LED strobes, has anyone seen the new Philips Showline SL 510?
    Apparently they'll be cheaper than the SGM X5, so I think in a year or 2, the writing will be clearly on the wall for traditional strobes.

    They use an SMD LED, anyone who knows about LED's got any idea what type?

    I was looking at the Showtec Technoflsh 448 a few months back which says it uses 392 pieces of '5050' leds. Anyone got experience of these and whether theyy would cut it in a bright strobe role?
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  6. #46
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    Tried doing a comparison Norty but ones in Lux and the other lumens, so I'm non the wiser which is a pity as the Philips is a definite contender as well for me.

    The philips look bright in the Youtube videos but on some chase effects, I prefer the ADJ as I don't personally like the small LED matrix effect.

  7. #47
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    Al, I think the Philips will be in a different league to the ADJ strobe.
    I still wish they would show strobes in action by showing the stuff being lit. they all have the facility to overload the camera when viewed from the front, so it makes it very hard to compare. I like what he did with the room in the ADJ video.
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  8. #48
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    Are there any predicted prices on the Philips units Norty? I searched the web but can't find any indications.

  9. #49
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    Cheaper than the SGM but that could still make them pretty pricey. I expect at least Atomic money.
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  10. #50
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    I might risk an ADJ unit then. £800 for a strobe is a bit rich for me especially just for at home.

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