Autor Tema: O svetlosti: Zašto su jeftine fluorescentne sijalice loše za fotografisanje?  (Pročitano 9042 puta)

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O svetlosti: Zašto su jeftine fluorescentne sijalice loše za fotografisanje?
« poslato: Februar 21, 2012, 10:56:58 posle podne »
Jedna zgodna i koncizna priča o teoriji spektruma... (hvala Zoranu Rodiću za link)

Pokazuje zbog čega su jeftine fluorescentne sijalice (čitaj: "štedljive") loš izbor za fotografisanje, ali i duži boravak u njima osvetljenim prostorima. Grafici pokazuju pokrivenost referentnog spektra sunčeve svetlosti, kako u odnosu na talasnu dužinu svetlosti, tako i njihovim intezitetom.

Pošto je originalni članak napisan na ruskom jeziku, verovatno ima i grešaka u prevodu (Google Translate). Ipak mislim da je suština dovoljno jasna:


Why cheap fluorescent lamps are poorly suited for taking pictures (+ a bit of the theory of the spectrum)


Gas discharge tubes (fluorescent lamps) are used everywhere. Previously, we only worked and studied in the light of this, and today the state is positioned as the standard energy-saving lamps and home lighting.
 
This is unfortunate, because many of these lamps is not only half-cycle pulse with a frequency of alternating current (due to low inertia of the glow), but also have discontinuous spectrum, all of which vision is tiring and does not provide the correct color. Today, many companies offer kits for photographers to shoot a subject on the basis of energy-saving lamps. And you can with 100% certainty that there used lamps are not polnospektralnymi high-quality light sources with a colorimetric point of view.    Why is it important and why I brought it all on the spectrum?

Many people believe that if the light source visually white and gray card-pointing after the pipette is neutral gray, then we have an exact color reproduction. But this is misleading. Let us turn away from our head, the reference star. In nature, there is only one natural source of light, bright enough and constant in time within the human existence as a species, so that you can regard it as a reference - it is the sun .    This spectrum of sunlight ( hereinafter spectra schematic):


The mixture is heated and ionized gas components that make up the Sun and its corona, its glow fills the visible spectrum, and even goes beyond it in the ultraviolet area.

In terms of colorimetry and color vision, this means that objects in different colors that lie within this range, and illuminated by sunlight, are seen as equally intense (of course, apart from the features of the psychology of color perception, which initially gives some color darker "character", and others - lighter). Theoretically, this provides the spectral linearity of the system, "the Sun - the subject - the eye (camera)."

This largely explains the fact that most cameras provide the best color in the sunlight (and do not forget that even in the matrix Bayer mosaic filter with its characteristic curve).

Close to the solar light flash . These flasks commonly used gas xenon, which has now such a spectrum:


The spectrum of a line, but the lines are quite frequent and uniform, to be regarded as relatively continuous. Excess cold blue of the spectrum is partially cut off by a special coating of yellowish color, marked on the bulb flashes. Incidentally, the quality of the flash, you can easily identify it on the quality of the coverage and accuracy of color temperature. The result is a nearly continuous spectrum, very close to the sun. Therefore, the flash can also be regarded as approximately correct colorimetrically light source. Light bulbs are almost hundred percent in terms of CRI (Color Rendition Index).

Here is the spectrum of incandescent light bulbs:


It is also continuous, but dominated by yellow-red light and not enough blue. Color adaptation of the human visual apparatus can partially compensate for this, although the color from purple to green will be perceived darker and warmer than they actually are. In photography, a low color temperature is easily compensated by a proportional shift in the processing of all colors in the cold part of the spectrum. Can use conversion filters. It is important that this is still the range of reproducible colors is continuous, as in the sunlight.    So, we looked at three sources, each of which gives a relatively continuous spectrum, and therefore preserves the relations, proportions, colors in general (although they all can move in warm or cold side). For these sources, the color temperature of light is completely or almost completely characterizes the tone and what impact they will have on the color reproduction when viewing or for photography. Accordingly, such a spectral shift is easily compensated by adjusting the white balance (ie - color temperature). Of course, it may make more visible photon noise, but the issue is already in a completely different field, and today we did not say.    Now let's look to what we want the world to teach environmentalists and the state (as well as manufacturers of cheap sets of constant light for photos and video).

So, drum roll! cheap energy-saving fluorescent lamp:


A strange picture, isn't it?

The light appears white because it does when adding color bands in the spectrum will turn white. But imagine that we cover in this light, photographed the scene - get that many colors in it generally will not be lit, corny "fall out". Incidentally, this is due to the fact that under the fluorescent lights so visible skin blemishes in portraits - just as it lost the intermediate sections of the gradients, the bright line spectrum of the "highlight" of the narrow shade and obscure failures are the same narrow region. Take expensive one:


In general, the situation is better, but still has a range of dips is almost deaf, where the color will be distorted, and transitions to lose plasticity. Moreover, these failures can not fix the white balance setting, there really is not even a profile will help. It is clear that in order to capture high-quality light sources are used not. And something tells me that the eyes are at least uncomfortable.

However, there are very good and very expensive fluorescent lamps that have a flat spectrum and a high CRI and are used for example as a reference light in the printing industry. Quality lamp and put a light in expensive monitors. But this is more the exception than the rule. Another serious drawback of fluorescent lamps is that they have low inertia of the luminescence and thus fed with alternating current, and hence a greater or lesser degree of "blink" at a frequency half-period of the lighting network. First, it is harmful to the eyes. Second, it creates two unpleasant effect. The first of these - the strobe when shooting video when the refresh rate of the matrix close to the line frequency, and the image appeared running band or flicker. The second phenomenon - it is "bouncing" the white balance between adjacent frames due to the fact that aging can be shorter than the oscillation period and capture the moment of extinction of light, which color temperature is very different from the original.

Recently appeared in stores, and even a very promising version - LED light bulbs :


The range of their almost complete, although there is a small failure, but on the whole quite adequate. Much depends on the manufacturer, but in general this type of light source is very promising, especially given the low power consumption and, consequently, the opportunity cost of the battery power on the road.

Great advantage of LED lamps is that, unlike fluorescent, they work from DC due to its principle of action and therefore does not pulsate half-AC, which means their light is constant and is suitable for video recording, without the effect of strobe, and there is no problem with a different white balance from frame to frame, as in fluorescent lamps. UPD: It is strongly recommended that you read and here this addendum , which I clarify some questions.



Originalni članak na ruskom jeziku: LINK
Preveden na engleski pomoću Google Translate-a: LINK

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Van mreže Zoran Rodic

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Odg: O svetlosti: Zašto su jeftine fluorescentne sijalice loše za fotografisanje?
« Odgovor #1 poslato: Februar 22, 2012, 08:14:06 pre podne »
Posle sunca i blica, ispade da je obicna sijalica najbolja u celoj prici. I ako sam svojevremeno konstatovao da najbolje rezultate postizem sa sijalicom, ali onom DayLight (u prilogu prikacena), ja sam to ignorisao i odabrao kontinuirano i kontrolisano neonsko osvetljenje.

Sad bi mogao malo da predefinisem uslove rada :) ... pa da ponovo isprobam ovu kombinaciju.
''Ne moze da svane pre zore''