I have just shared a new project: “Salvaged Street Light Conversion”
IntroductionI salvaged some decommissioned street lights from the local transfer station. I suspect they adorned the main street of Woodend in the past and would now look good in our garden. They were banged up but mainly intact.
So I straigh…
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Hi @MarkMakies
Very neat conversion.
As a lighting engineer, and as a theatre lighting designer, I think that your partners ‘guidance’ re the designed appearance of the illumination is a great choice.
I must admit I also like the warmer colour temperatures in my household lighting - the current fashion for ‘sharp, white light’ is an uncomfortable choice for the living environment.
FYI here is a basic colour temperature chart for reference.
High Pressure sodium lights operate at about 2700K with a colour rendering index of about 85 (out of 100)
Low pressure sodium lights operate at about 1700K, and being monochromatic, have a colour rendering index of 0.
Cheers
Murray
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Hi Murray,
Thanks for the feedback. I never looked into the colour rendering index or knew much about it until now. I suspect that the CRI obtained from the GlowBits is pretty low given RGB values are 255,139,21 and the fact that the LED’s have a kind of discrete emission output.
Even though my Nikon SLR shows a similar colour temperature (reflected off a standard gray card) to the other commercial lights, it looks very red to me, especially indoors and in certain outdoor natural lighting conditions.
Can one easily measure CRI, or is specialist equipment required?
Cheers,
Mark
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Hi @MarkMakies
CRI is ‘interesting’ as it tries to represent how a coloured surface visually appears under a specific light source, when compared to the same surface viewed in ‘daylight’. Think of someone buying something, and asking if they can take it outside to look at it to ‘check the colour’. This was particularly prevalent in the early days of fluorescent lighting as they often had a nasty greenish tinge.
It was originally quite subjective, as there was no simple way of determining it empirically.
Now there are very specific measurement criteria and processes for it, but it can still be contentious.
Here are some useful links describing what it is, and how it is currently determined. And why it can be very important, i.e. hospitals etc.
And colour temperature is also interesting since technically it can only be applied to a black body radiator as it heats up. But by plotting the colour spectrum of a given source onto the CIE chromaticity diagram, and determining ‘how close’ it is to the black body line, an ‘equivalent colour temperature’ can be assigned to the source.
This is only an approximation, since most current sources do not have a continuous spectral output - there are gaps and peaks rather than a smooth, continuous output.
LEDs are in the ‘do not have a continuous spectral output’ category.
Here is the CIE chromaticity diagram, the black line is the black body temperature line. (the equal energy point is defined as ‘white’)
Hopefully not too much info (TL;DR)
Murray
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Hi @MarkMakies
Here is a simple visual image comparing light sources at various (simulated) colour temperatures
Murray
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It appears that this design may not be suitable for a permanent outside deployment. To date, 3 modules have melted down. In a few cases I suspect a power surge down the 100+m of wiring has taken out the DC convertor.
In this case the convertor on the MPU board has blown. Maybe a code glitch caused the entire LED array to light up, which due to the current would fry the reg. I know better than to design a system which would allow a software glitch to destroy hardware - this is what happens when you take short cuts!
For a permanent solution I would use a better protected and resilient DC convertor which would also provide power for matrix, rather than through the MPU module. And a few TVS diodes wouldn’t go astray.
Looks a lot worse on the back
mark
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Hi Mark
It probably has nothing to do with your present situation but do you think it is a good idea to reticulate DC voltage around your installation.
There is a very good reason your household mains and house wiring is AC. And have you noticed (particularly on this Forum) that all control devices like water valves etc used in watering systems where the humidity could be high (indoors) are 24VAC, NOT DC.
I note you seem to have minimised the potential problem by soldering the DC connections but if you have any screw type connections I don’t think they will last long before the positive wire becomes black with oxidisation and eventually fail. I don’t think soldering the connection eliminates the problem completely but would delay any damage.
Cheers Bob
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I found this so interesting.
Thanks for sharing 
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Hi Murray.
Jumping on this thread because I’m interested now too.
Does the hue of a light, like an LED, change as you move further away from it?
Hey Bob,
Absolutely right and I would run 48VAC if I could. My irrigation is all 24VAC solenoids and other systems are PoE or solar/battery, both DC.
However I’m stuck with a lot of legacy stuff on this particular circuit that I don’t want to fiddle with, because it’s working fine. At house end 18VDC and at the far end 10VDC, mainly due to a high load and high wiring resistance in some critical long runs. So nowhere near ideal, but if it ain’t broke I don’t fix it.
mark
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This pic gives you an idea of how the light renders this scene, especially with the moon in the background, and a black cloudless sky for reference.
It kind of looks like this pic for real, strangely, until Murray’s post anyway.
mark
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Hi @Pixmusix, @MarkMakies, @Robert93820 et al,
The question was: Does the hue of a light, like an LED, change as you move further away from it?
Short answer: No
Longer answer below:
The word ‘colour’ is meaningless to a blind person and it is dufficult to explain in text (…) a subject which can only properly be described by personal expression and comparison. The fact that natural adjectives are often used to describe colour illustrates the basic difficulty in attempting to specify colour in technical terms. Even when the technical terms are understood, the description ‘blood red’ gives an inaccurate but more acceptable impression of a red colour than (…) CIE 0.6x, 0.3y.
(Ch 3 introduction, Lighting (3rd Ed.) by D C Pritchard ISBN 0-582-30529-2)
Having said all that, one also considers some of the various methods of ‘defining’ colour
- CIE tri-chromaticity co-ordinates (very mathematical)
- Munsell Colour system colour atlas with Hue, Saturation, and Value figures, based on comparing paint samples
- Printing inks using Cyan, Magenta, Yellow and Black inks (CMYK)
- Pantone colour swatches as used in the graphics, marketing and art industries
- Theatrical filter gel swatches used with stage lighting equipment
- RGB numbers vs HSV numbers vs CMYK numbers vs CSS codes
- etc etc …
However, if we generate a particular colour (a.k.a. a ‘hue’) with a light source (i.e. a LED), and given certain pre-conditions we can state the following:
- the light source and all measurements are shall be in an environment that is a perfect vacuum.
- if it is a mono-chromatic source, it shall emit only a single frequency of light (electromagnetic) radiation.
- assuming it to be a point source, it shall radiate a given quantity of light equally distributed in a completely spherical pattern (a 4*pi steradian solid angle).
- the intensity of light emitted in a particular direction at a particular distance can be calulated, based on the original quantity and the original distribution pattern.
- if the measuring distance is doubled - all other factors being equal - the measured intensity will be one quarter of the previous value. (This is the Inverse Square Law in action)
Nothing in the above statements changes the frequency ( the apparent colour or hue ) of the light emitted by the source, so answering the question again;
Does the hue of a light, like an LED, change as you move further away from it? No.
And in the typical test environment here on earth, in air rather than in a vacuum, the answer remains (effectively) No.
What does change is the intensity as the distance increases (which is perceived by the eye as ‘brightness’, not intensity), and being human, we often register the decrease in brightness as a small change in colour - “It doesn’t look the same”.
NOTE: we are still only considering a mono-chromatic source here - it only radiates a single frequency.
Going on further … . (TL;DR)
What can happen with ‘real’ sources, ones that are not a mono-chromatic source, is that
(a) the ‘red’ (or ‘green’ or ‘blue’) light emitted actually is a related range of frequencies (including some that may be very unrelated to the basic perceived colour), and
(b) the air itself, pure and/or with various chemical contaminants present, can absorb certain frequencies of light (a.k.a. electromgnetic radiation).
This occurs because the energy in the radiation can cause certain temporary changes in the energy structure of atoms, and by doing this ‘work’, be reduced or lost from the overall emission, thus causing an actual change in the range of frequencies that were originally emitted by the source. And so the perceived colour ‘changes’.
N.B. LEDs are not mono-chromatic.
This would be more noticeable with a more general light source, and over a great distance. The frequencies ‘most likely’ to be absorbed are the higher frequency (more energetic) ones, i.e. the blue end of the spectrum.
Wrapping up:
- With a real source, in the real world, in the strictly technical sense, yes the range of frequencies received MAY not be equal to the range of frequencies emitted. The ‘colour’ changes.
- With a real source, as perceived by a human eye, an actual colour change is probably not distinguishable. However, human perception, pre-conceived impressions, and environmental factors may cause the observer to decide that the colour has changed.
- Describing the apparent change to someone else may be problematic and cause disagreement (refer to the intro paragraph)
Murray
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This is great writing. I think this gets to the heart of it for me.
I now realise that, even though it is not what I wrote, I was wanting to ask about our perception of colour over distance… I was trying to ask about a psychological effect in an empirical way but the questions isn’t sensible.
So to repeat this in my own words to make sure I understand:
The hue of an LED is governed by the physical property: frequency of the emitted light. We talk about hue in this way, because it’s the only objective/universal way that we can discuss it. In this way distance can’t really effect the hue of an object just it’s luminosity.
Did I get that right?
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Ah interesting point. I had to write about similar topic very recently regarding laser safety over distance.
When it comes down to it, at the end of the day, colour is determined on the wavelength of the wave or frequency the photons are resonating at (because we model light as both a wave and a particle at once thanks to the (in)famous double-slit experiment illustrated below for posterity with a link to the wiki page for people to read more)
The cones and rods in the retina of your eye become excited by these photons/electromagnetic-radiation when they’re absorbed which then go down your optic nerve as signals, depending on what those signals are (highly simplifying this of course), your brain recognises light hitting a particular part of your eye as some colour and intensity which is how we see.
That is exactly right, and luminosity (measured in lumens, lux, candela) is really just a measure of intensity (well sort of but not really). In non-relativistic environments (speed or extreme astronomical distances) no, light travelling through a vacuum will always remain the same colour.
However, travelling through a nitrogen rich atmosphere as Murray noted, or through water, etc. certain wavelengths of light will be absorbed and scattered which is why we see the sky as blue. So in that sense, yes, if you take an LED kilometres away it’ll appear more blue although it should be nearly imperceptible (especially if there was very little blue light being emitted to begin with).
There’s one other condition which is at relativistic speeds at which you’ll get red shift or blue shift from the doppler effect, although the LED wouldn’t be around for long if travelling close to 3x10^8
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Unfortunately you are mis-using another technical term …
Luminosity is an absolute measure of radiated electromagnetic energy (light) per unit time
Your concept is correct here
What you are talking about is Luminance and Brightness
Luminance is a mathematical and measurable quantity which is the quotient of Intensity and projected area
Brightness is a physical sensation perceived by the eye and interpreted by the brain according to which a surface appears to emit more or less light
and the ‘correct’ wording you should use is:
In this way distance can’t really effect the hue of an object just it’s luminance (mathematically) or its brightness (by perception).
Murray
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Oh interesting!
I’ve always used brightness and luminosity interchangeably.
Learnt something.
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Noted - I should have added another pre-condition
- the source and all measuring systems are absolutely stationary relative to each other.
no relativistic perturbations please
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My mistake, thank you for the clarification 
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Yep, it is generally a consideration outside of astronomy or particle accelerators. Thought I’d bring it up out of interests sake for anyone curious 
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I can’t remember where I first learned about this experiment.
Right up to this day, I find it haunting information.
It’s very woo woo; It’s also very very, scientifically so, real.
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