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eGospodarka.plGrupypl.misc.elektronikaoswietlenie LEDRe: oswietlenie LED
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    Date: Thu, 26 Jul 2012 00:33:43 +0200
    From: Paweł Pawłowicz <p...@w...up.wroc[kropka]pl>
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    Subject: Re: oswietlenie LED
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    W dniu 2012-07-25 23:53, Ghost pisze:
    >
    > Użytkownik "J.F." <j...@p...onet.pl> napisał w wiadomości
    > news:1iy4c6hkaq1eb$.1cxmb6k20n4wz$.dlg@40tude.net...
    >
    >>> a kandela jest liczona w scisle okreslonej czestotliwosci,
    >>
    >> Eeee, jakiej ?
    >
    > http://pl.wikipedia.org/wiki/Kandela

    Nie chcę być nieuprzejmy, ale nic nie rozumiesz. Tu masz parę słów
    wyjaśnienia:

    The simplest way to proceed is to note that illumination
    engineers measure illuminance in units of
    lumens per square meter or lm/m2, and this flux is
    defined as a lux (lx). Therefore, the
    lumen , under certain conditions, is proportional
    to energy per second, and it looks a bit like a watt.
    The difference between watts and lumens is that
    a watt of green light appears to be much brighter
    than a watt of red light, while lumens have been designed
    so that a lumen of any color in the visible
    region appears to be equally bright. Th is sounds like psychophysics,
    and it is. We have to ask human
    observers to match the brightness of different
    colors of light, or to measure by some means the
    sensitivity of the average human eye to light of different
    frequencies. This has, in fact, been done for
    light-adapted (photopic region) and dark-adapted
    (mesopic region) human eyes. The standard lm is approximately 1/683 W or 1 W
    produces 682 lm at 555 nm, and values for the other
    wavelengths are based on the photopic luminosity
    curve. For example, at 400 nm, 1 W produces 0.27
    lm, and at 700 nm, 1 W produces 2.8 lm.
    Suppose a light beam containing a variety of colors
    (wavelengths) is viewed by a human observer.
    Furthermore, let the spectral-power density be
    given by the function J(?) in watts(unit wavelength).
    The apparent brightness of this beam can
    be computed if the standard luminosity function
    y(?) is known:

    Flux(lumens) = 683 ?y(?) J(?)d? ,

    where the range of integration is 400 nm to 700 nm.
    This just means that each increment of the powercurve has to be adjusted
    by the luminosity curve
    before it is added to obtain the total number of
    lumens.
    Th is comparison of units is necessary for understanding
    the characteristic curves for film and
    sensors. However, I have not related the lumen to
    the other units in common use. This is tedious, but
    necessary for understanding the literature. Consider
    a light source at the center of a sphere having
    unit radius. If the source emits 1 lm/steradian uniformly
    in all directions the output is defined as 1
    candela (cd). (A steradian is defined as the solid
    angle subtended by 1 m2 on the surface of a sphere
    having a radius of 1 m.) Furthermore, 1 footcandle
    (fc) is defi ned as 1 lm/ft2 just as we defi ned 1 lux
    as 1 lm/m2.

    Pozdrawiam,
    Paweł

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