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