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Thread: Xt-E Bulb, anyone?

  1. #1
    Flashaholic* degarb's Avatar
    Join Date
    Oct 2007
    Akron, Ohio

    Default Xt-E Bulb, anyone?

    in 2000ish, I got rid of all my incans for CFL's. Now, I want to dump these 55 lpw electric hogs for something closer to 140 lpw. The bug has bitten me.

    I want 5 watt light bulbs that put out 450 lumens, or more! And, 2 watt light bulbs with 250 lumens!

    So, the Cree xt-e is cheap and 140 lpw; when will we start seeing these in $10 or under bulbs? Comon manufactures!
    Some people are all lumens and no lux, while others are all lux and no lumens. Some just thank God they have neither.-- All of my lights have throw--some pretty darn far, into the garbage.

  2. #2

    Default Re: Xt-E Bulb, anyone?

    The problem is that absolute efficacy of the latest emitters just doesn't translate directly into OTF (out the front) lumens of LED bulbs. It slowly trickles into the market, but right now we're averaging maybe 70 lumens per watt in the $20 category? I'm also cheering to get these things to at least break the 100 lumens per watt barrier before I get my AARP card, but manufacturers have to make their profit first

    Just another cool emitter to build a wacky lamp with though.

  3. #3
    Flashaholic* LEDninja's Avatar
    Join Date
    Jun 2005
    Hamilton Canada

    Default Re: Xt-E Bulb, anyone?

    " the XT-E LED delivers up to 148 lumens and 148 lumens per watt in cool white (6000 K) or up to 114 lumens and 114 lumens per watt in warm white (3000 K), both at 350 mA, 85°C."

    'UP TO ...' is a dead giveaway that most of the production units are way below the quoted number or the wording would be 'MINIMUM ...'.

    '114 lumens per watt in warm white (3000 K)' Most A style LED light bulbs sold in North America is warm white/soft white to closely match incandescent tints. So you are down to 114 LED lumens per watt or less.

    Now your power in is 115VAC. There are losses converting it to the required DC. This is made worse by the requirement that electrical equipment needs to have a power factor of 0.9 or better in North America. Figure in another 15-25 % loss bringing your lumens per watt down below 97 lpw.

    Then comes your optical losses. The venerable Maglite had been tested in both incan and LED versions and only 65% of the LED lumens come out the front. While LED A style bulbs are not as bad a loss of another 10% would bring lpw below 90. That is the best case.

    So much for an XT-E bulb producing 140 lpw.

    BTW for maximum efficiency LEDs and their electronics need to keep cool. So a big heatsink is a must. Take a look at the SIZE of Cree's prototype light bulb:

    The most efficient bulb on sale right now is the Philips L-prize winner. MSRP is $60 though you can get it for $50. The bulb is using high efficiency cool white mixed with red LEDs to get to 94 lpw. The extra complexity means it won't go under $10 anytime soon.
    Keep an eye out for coupons for this bulb in your electricity bill. Should bring the prize down to $22 to $25.

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