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Thread: Down lights, 220v lamps in 12 volt fittings?

  1. #11
    Diamond Member AndyD's Avatar
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    Quote Originally Posted by murdock View Post
    and does anyone know why they make it with a glass cover?
    I'll stand to be corrected but I think it improves the colour rendering and the efficiency by reflecting the UV portion of the emitted spectrum back at the filament. In the earlier days of this type of lamp they also used to be more prone to exploding when the filament failed so the glass cover shield also offered some user protection if this happened.

    I'm not sure about the temperature difference but I don't think there would be one. There's a direct relationship between filament temperature and the colour of the light, the colour is given as a temperature in Kelvin. Warm white is around 2500K upward and as the temp increases above 4500K it becomes cool white. Eventually as you get hotter you get 'daylight' colour around 7000K so to answer Martinco's question, if the filament temp was higher then the light colour would be different.
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    Gold Member Martinco's Avatar
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    Are you then saying that in theory a warm white should last longer than a daylight due to the lower temperature ?
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    maybe one of the reasons for the glass cover is that it can then be used in bathrooms.the open type are not allowed.

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by Martinco View Post
    Are you then saying that in theory a warm white should last longer than a daylight due to the lower temperature ?
    That's a damn good question and I honestly don't know the answer for a fact. From what I remember of my somewhat blurred university days mean time to failure analysis curves are generally kinda logarithmic in shape. In other words there's relatively little difference in failure times within a certain band of operating variables....but, and it's a big but, as soon as you exceed a certain threshold for a variable such as operating temp then the mean failure time would decrease very rapidly with even a very small temp increase.

    Sounds complicated but it's not; take a car for example, if unmaintained it might run failure free for 100,000 km if driven at a constant 2500rpm. At 5000 rpm it might run for 95000 km without failure but as soon as you go past the red line to 6500rpm it might only run for 10000 km before it fails, at 7000rpm the engine might only last 20km and at 8000rpm only 100 meters.

    I'm guessing that the lamp OPERATING temperatures within the colour temperatures of warm white through to daylight would fall under the 'red line' of the lamps design so differences in mean time failure rates would be insignificant.

    Quote Originally Posted by bergie View Post
    maybe one of the reasons for the glass cover is that it can then be used in bathrooms.the open type are not allowed.
    I think they're legislated for bathroom use because they're more splash-proof/shatter proof with the glass cover shield.
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    someone once told me that the reason for the glass was to disapate the heat...the glass was used where they wanted the heat to go up into the roof space and the ones without the glass were used where the light was fitted in a confined roof space...so the heat could go go down...i dont know how tru that starement was...after doing some research...i was told that according to the european standard it is a safety requirement...for when the lamp explodes it contains the small pieces of the lamp...sounds logical...but you never know what to believe.

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