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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorTonyt
    • CommentTimeDec 12th 2011
     
    <blockquote><cite>Posted By: Gotanewlife</cite>Gusty what are you on: "watts are meaningless...you only need the lm". Grief man, I think I'll give up - except because its you I'll blame it on a bad hair day - you do have some hair I presume......

    2 LEDs, identical specs, manufacturer, certifications etc, identical aside from from Watt value. First LED has 290lm second has 300lm - which one is best Gusty? Can't tell can you? The answer is in one of my posts above as these 2 bulbs actually exist.</blockquote>

    Gotanewlife,

    Bulbs go in the ground, lamps go into light fittings
    •  
      CommentAuthorJSHarris
    • CommentTimeDec 12th 2011
     
    <blockquote><cite>Posted By: Tonyt</cite>Will some post a link to all these great leds they are buying? </blockquote>

    No direct link, but a look at this thread will get you a good start on where we're shopping:
    http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=7769&page=3

    It's a bit of lottery deciding what to buy, and Alibaba gives you a staggering array of choices, but there are definitely bargains to be had.
    • CommentAuthorGotanewlife
    • CommentTimeDec 13th 2011 edited
     
    <blockquote><cite>Posted By: Tonyt</cite>Will some post a link to all these great leds they are buying?</blockquote>

    OK here is the order that just arrived:

    http://www.aliexpress.com/product-fm/495888808-best-selling-10pcs-lot-new-design-100-Cree-led-chip-cool-white-gu10-9W-LED-light-wholesalers.html

    9W (made up of 3x3w), CREE Chip, 800lm, they told me 50,000 hrs. Non-dimable (dimables don't last as long LP told me). I bought cool white and 45 degree lens. I paid $174 plus 26 Euros for 30 luminaries. Note, however, I did a deal through live chat to pay zero for DHL courier delivery for 30 items. Also they completed good customs paperwork in English which prevented me filling out 2 forms here before they would deliver. Finally they kindly stated without me asking that the total value of the goods was $30, ie $1 each - and that saved me a load of tax too. In all then about £4.55 each (depending on the exact exchange rate).

    How long will they last - don't know but at least as long as the EBay ones.

    They cost less than my 3w ones, same chip. Gusty, I really don't think price can be used to gauge efficiency (ie lm/W), even if it were a perfect market, which it most certainly isn't. Obviously I am a novice at all this but for me and any other novices I think it is ESSENTIAL that the lm and the Watt value are known before buying an LED luminary.
  1.  
    One quick suggestion: when shopping for LEDs, try to determine the "colour rendering index (CRI)" of the light. To quote wikipedia: "The color rendering index (CRI) (sometimes called color rendition index), is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source".

    If you've wondered why some LED lamps produce a slightly "spooky" light (where skin tones look slightly pale and ghostly and food can look distinctly unattractive), it's probably because that lamp has a low CRI.

    A few manufacturers state this metric; if not try to determine which LED chip the lamp manufacturer uses and then look up the CRI for that chip. (Personally, I think all lamp manufacturers should state CRI on the packaging).

    Some examples (from WikiPedia):

    A Low pressure sodium lamp has a CRI of ~5
    A basic halophosphate warm-white fluorescent has a CRI of around 51
    A posher tri-phosphate warm-white fluorescent has a CRI of around 73
    An incandescent lamp has a CRI of 100

    LEDs seem to have CRIs from around 50 to 92.

    Basically: the spectrum produced by an incandescent lamp is a smooth continuum from IR to violet. The spectrum produced by LEDs and fluorescent lamps, on the other hand, is "spiky". You can produce a light which looks, at first glance, like white light by having a spike of red, green and blue; but this light will fail to render objects with realistic colours. When viewing familiar objects like the skin of other humans or the food on our dinner plate, a serious deviation in colour rendering can be distinctly unpleasant. I've heard people refer to LED light as "spooky" or "ghostly" or "artificial". I'd be willing to bet that what they're perceiving is a low CRI.

    Building an incandescent lamp with a CRI of 100 is easy. Building a CFL or LED with a high CRI takes some serious engineering effort.

    Colour perception is an interesting and complex beast.

    http://en.wikipedia.org/wiki/Color_rendering_index
    http://en.wikipedia.org/wiki/LED_lamp#Remaining_problems
  2.  
    Fiar point. I would try and purchase a sample initially every time before a larger purchase. If you are buying from China then you can usually buy a sample in the UK to save on shipping and hassle factor. When you are happy then go direct. This is providing you are sure the LED's are exactly the same though!!!!
    •  
      CommentAuthordjh
    • CommentTimeFeb 24th 2012
     
    Posted By: dan_aka_jackA basic halophosphate warm-white fluorescent has a CRI of around 51
    A posher tri-phosphate warm-white fluorescent has a CRI of around 73

    Right, but that's because you have chosen lamps that are designed not to render colour correctly! In the same list, if you choose instead

    Tri-phosphor cool-white fluorescent 4080 89

    you get a better figure for triphosphors, if you actually wanted one that renders colour properly. And if you want better, there's always places like http://www.topbulb.com/find/cri.asp

    Also, women's eyes are better at colour discrimination, so get their approval :) (that's in general rather than individuals. They may have an extra cone type http://en.wikipedia.org/wiki/Tetrachromacy )
  3.  
    Posted By: djhRight, but that's because you have chosen lamps that are designed not to render colour correctly! In the same list, if you choose instead

    Tri-phosphor cool-white fluorescent 4080 89

    you get a better figure for triphosphors, if you actually wanted one that renders colour properly. And if you want better, there's always places like http://www.topbulb.com/find/cri.asp


    I totally agree. Sorry, I didn't meant to give a biased view; I just wanted to select a small handful of lamps as a quick example.

    I definitely agree that the top-end of fluorescent technology currently outperforms the top-end of LED technology in terms of colour rendering. I have some Philips TL-D 90 Graphica Pro Triphosphor linear fluorescents with a CRI of >98 in my office and they're gorgeous. If I had my way, I'd use linear fluorescents with high frequency ballasts in every room of the house. The tubes are far cheaper than LEDs (a 2 foot 18 watt Graphica Pro is only £8), have excellent colour rendering and are dimmable with the correct ballast. Not quite as efficient as the most efficient LEDs though (the graphica pro produces 950 lumens at 18 watts = 53 lumen/watt; it seems you have to give up some efficiency to achieve a high CRI with fluorescents; some fluoros have an efficiency of around 100 lumen/watt)

    *update* It looks like LEDs with a CRI of 98 are being developed:
    http://www.ledsmagazine.com/news/8/10/15
    http://news.thomasnet.com/fullstory/Stem-Mounted-LED-Lighting-Fixtures-offer-CRI-of-98-596383

    And an interesting thread about using 92 CRI LEDs: http://www.candlepowerforums.com/vb/showthread.php?298253-Nichia-High-CRI-119-LED
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