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Thread: NRC Report - Assessment of Solid Sate Lighting

  1. #1
    Flashaholic
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    Default NRC Report - Assessment of Solid Sate Lighting

    https://download.nap.edu/catalog.php?record_id=18279

    Reading Online or downloadable PDF is free but you have to supply a name and EMail address.

    While the entire report is worth reading - the backgrounder info on color rendering was very helpful to me. We have a lot of discussions/arguments at CPF on what constitutes the best source(s) for true/accurate color rendering. Here is a particularly relevant excerpt(sorry for the formatting - copied from PDF).


    Good color rendering can be achieved with such discontinuous light spectra because of the properties of the other two elements in the process of perceiving object colors: the
    reflectance of the objects and the absorption of the cone
    photopigments in the human visual system.
    All objects, natural or artificial, reflect as a function of wavelength in a
    very broad and continuous manner. The reflectance factors of
    these objects (the proportion of light reflected as a function
    of wavelength) do not show sudden spikes or isolated dips
    in reflectivity across the visible spectrum. Because of this,
    the general shape of the reflectance factor can be interpolated
    with fairly coarse wavelength sampling.

    The three cone photopigments responsible for color vision have absorption
    functions that are very broad, continuous, and overlapping
    in wavelength sensitivity. Each cone type responds to many
    wavelengths, although sensitivity does change depending
    on the wavelength. The outputs of these photoreceptors do
    not signal the wavelength composition of the stimulus to the
    brain. For instance, a certain level of activity from one cone
    type could result from a small amount of energy at every
    wavelength it is sensitive to or a lot of energy at only one
    wavelength it is sensitive to. The visual system makes absolutely no distinction between these two situations (Rushton, 1972).

    The perception of color arises from combining and
    comparing the activity among the three cone types. There-fore, countless combinations of input wavelengths can lead to the exact same perception of color. These circumstances,
    in which objects reflect in a fairly predictable manner and
    the visual system interprets incoming light in terms of three
    broadly sensitive channels, allow a great deal of flexibility
    for the spectral content of light sources.

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    Flashaholic* uk_caver's Avatar
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    Default Re: NRC Report - Assessment of Solid Sate Lighting

    I guess that (depending on the person) when it comes to colour rendering there may be quite a distance between 'good' and 'best', or even between 'good' and 'adequate'.

    Personally, I only tend to notice colours looking 'wrong' rather than 'different' when it comes to LED lighting of foliage, where compared to daylight, colour contrasts between various things may decrease or increase, and some colours can seem strange even bearing in mind the mind/brain's fairly serious ability to generate colour constancy.

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    Flashaholic* Lurveleven's Avatar
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    Default Re: NRC Report - Assessment of Solid Sate Lighting

    You will never get foliage etc. to look like daylight, simply because the difference in light direction. The underside of branches/leafs may also have different color than the top, and at daytime the underside is only lit by ambient light while the top is lit by direct light. At night time, when you shine your flashlight, you may shine more on what is left in the shadow at day time, and less on what is lit up at daytime, so things will look different and some things you will see much better at night with a flashlight. You should also notice how things look different during the day as the sun changes position.

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    Flashaholic* uk_caver's Avatar
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    Default Re: NRC Report - Assessment of Solid Sate Lighting

    In one way, I should notice how things look different under varying natural lighting conditions, and when I make an effort, I do, but then my visual system is putting a great deal of work into making things not look different under different lighting conditions, since the practically useful things to see are the constant optical properties of objects, not the colours of light coming from them at any particular time.

    I like LED lighting, and find it good for lighting most things, but there do seem to be particularly weak areas depending on the LED.
    When doing some experiments with a few self-built headtorches a while ago, I shone them into my garden to see how they looked at different power levels.
    One was cool white (Cree 1A or 1C), and a couple of others were neutral through neutral-warm.

    On one target (branches/twigs and a trellis in front of a wooden panel fence), with the warmer LEDs I could distinguish things quite clearly in terms of colour, but with the cool white it was much harder to tell what was what - even though there were some intensity differences, everything seemed to be almost the same hue of brown.

    It might well be that the 'real' difference between, for example, incandescent and LED lights or one kind of LED and another might not be too great, but that even for incandescents or warmer LEDs the visual system is on the limit when it comes to making things look 'normal' and some LED lighting is a step too far, especially for natural scenes.

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