Amber LED

[peza2010]

I have heard two different reasons, for why amber leds are being added to led gear, and why gear with the added amber LED's are usually more expensive.

One thing I have heard is the Amber helps create a more realistic "white" colour.

and the other is that when amber is added to RGB LED units, these can then "handle" video.

 

Which of these is true if any?

 

Thanks

[Just Some Bloke]

The first is certainly true: you can mix relative amounts of blue and amber to give you a mix between warm white and cool white (though to get the best white from LEDs then white LEDs are the way to go).

 

The second I'll leave to others.

[musht]

Amber lets you hit some of the more pastel colours, amber LED on its own isn`t terribly efficient so its an add colour to get inbetweens of Red /Green mixing,.

 

Video only has an RGB signal, extended gamuts on some stuff uses processing tricks to use the additional channels , but source will still be RGB.

[Tomo]

Amber lets you hit some of the more pastel colours, amber LED on its own isn`t terribly efficient so its an add colour to get inbetweens of Red /Green mixing,.

More colours gives better light - there are some good articles around about lighting with narrow-band emitters.

Amber itself is generally a very wide-band colour as it's not a 'native' LED colour, but made with phosphor(s).

 

The extra colours allow you to illuminate actual objects (and people) and get much closer to seeing them the colour they actually are.

RGB is (perhaps surprisingly) very bad at this - on a white or neutral grey surface it looks fine, but illuminating real pigments often gives strange results.

Video only has an RGB signal, extended gamuts on some stuff uses processing tricks to use the additional channels , but source will still be RGB.

Not strictly true - most video signals are natively in the YUV space or derivaties thereof (eg. MPEG works in that space).

 

However, the phosphor colours in your CRT telly are RGB, and they are also the colours in the vast majority of displays.

Unless you bought an extended-gamut TV in the last few months, your current TV is also an RGB display device.

 

Some manufacturers have very recently started adding amber to their high-end TV displays, which processes the YUV slightly differently to give a wider gamut, claiming to give better flesh tones.

 

However, the broadcast engineers are not currently using that kind of display as their reference monitor in the studio so how accurate that processing can be is a matter for discussion - and personal taste.

[adam2]

Amber LEDs come in two types, those made of the correct materials to emit amber light, these have existed for decades, though only fairly recently in high enough outputs for lighting.

The other type is a deep blue or near UV LED covered with a phosphor coating so as to convert the blue/uv into amber. These are a recent development.

 

Either type may be used and both have their advantages.

 

In theory any colour may be mixed from suitable red, blue and green sources. In practice though the available R/G/B LEDs are not of the right colours to achieve this accuratly.

The addition of amber and/ or white LEDs gives a considerable improvement.

 

The use of 4 or 5 colours of LED adds to costs and may require more control channels. It also may reduce the intensity of saturated coulours, since for example deep blue uses only the blue LEDs, these must be less numerous within a lantern of fixed dimensions or power, if 4 colours are fitted rather than 3.

[Tomo]

In theory any colour may be mixed from suitable red, blue and green sources.

Not true, actually. Colour is seriously complicated.

In theory a large variety of colours may be simulated using suitable Red, Green and Blue.

The variety of colours available from a given colour mixing system is known as the "Gamut".

 

The CIE range of colours known to be distinguishable by a human is shown below in grey.

The range of colours available to a normal sRGB video monitor (and an RGB LED fixture) is the region shown in colour.

http://upload.wikimedia.org/wikipedia/commons/d/d3/CIExy1931_srgb_gamut.png

(Around the edge are the wavelengths of light at each location, and across the bottom is the "Purple line" of 'virtual' colours that are not a specific wavelength but can only be made by mixing.

 

You will note that it's triangular, and doesn't come anywhere near filling the grey area.

 

The shape of the gamut is defined by the number of emitter colours - each one adds a corner to the available gamut.

The 'purer' the colour (ie the narrower the band), the closer to the edge of the grey area - a colour made up of a single wavelength of light would be right on the edge. (Some of the original work was done using monochromatic lasers)

 

This is true of all three-colour LED luminaires, though the exact location of each corner varies depending on the chosen diodes.

- You more or less get to pick whether you want a good yellow or a good cyan.

 

So, if you add more emitters, you can get even more colours.

- For example, Amber means you can go with an RGB trio giving a better cyan, and fill the gap with Amber.

 

Secondly, so far all this is merely simulation.

Simulated colours are great if you're looking straight at them, or using them to light neutral grey or white surfaces.

However, when it comes to lighting pigmented objects, they suffer limitations because not all the colours exist in the illuminating light, so the apparent colour of the object changes even though you're lighting it with light that looks to be the 'same' colour as an equivalent gelled tungsten luminaire.

 

As an extreme example, if you make a light that has adjustable brightnesses of 480nm Blue and 575nm Yellow, you can trim it quite easily to get what appears to be a reasonable white when you look straight at it.

Use it to light a deep red object though, and it doesn't work because there's no red light there.

[adam2]

Yes, I had oversimplified the matter.

However looking at the informative figure in the previous post, it may be seen that ALMOST any colour can be mixed from SUITABLE RGB sources.

One would have to choose LEDs or other sources very close to the "corners" of the triangle in the figure above. Linking the three sources with staight lines in the diagram would then include ALMOST all the colours visable to the eye.

 

Red and blue LEDs are available that are at the extreme ends of the spectrum, but these are not widely used because the perceived brightness is low for a given power.

The human eye does not respond well to wavelengths at the extreme ends of the spectrum.

 

Blue leds in practice stimulate the green receptors in the eye to an extent, unless LEDs of a very short wavelength are used.

Most red LEDs stimulte the green receptors in the eye to a limited extent, unless very long wavelengh reds are used.

[musht]

Really are limited to the triangle formed by the points, to stretch the triangle need to move the points further out or add more points.

 

Tomo has politely not mentioned , as he is involved with ETC, Selador the 7 colour LED luminaire line ETC now own.

 

http://www.etcconnect.com/products.ledfixtures.aspx

 

Sure there is some gamut diagrams buried on the ETC site somewhere........

 

CRT, LED, LCD and Plasma screens all have a limited colour gamut relative to the real world but human brain is good at guessing what`s meant.

 

Other thing about CIE diagram is it is from the 1930`s there is now an idea that we may be able to see more blues than were obtainable by 1930s light sources and the diagram is under review.

 

Yellow phosphor LED is stil relatively rare , be suprised if lower cost amber stuff uses phosphor LEDs rather than `conventional ` amber:

 

http://www.ledmuseum.candlepower.us/led/ledyel.htm

[musht]

When is orange actually brown or vice versa, why RGB can look like colour

 

[Tomo]

Thanks musht.

Yes, Selador is intended to fill exactly that gap in the LED market. (A few other manufacturers are also going that way, though most appear to have stopped at adding Amber and a multi-phosphor White)

 

If you'd like to see some in use, the ITV Daybreak studio is almost entirely lit with Selador, and you can see the fixtures in many of the wide shots.

 

The original work in the 1920s resulted in the CIE 1931 XYZ colour space (Z is omitted from the above diagram).

- There are also a lot of useful distortions of the original diagram to show things like 'perceived difference' between colours, among other things.

 

There is a lot of very interesting reading on the subject, if you want to investigate further.

 

There's also more 'raw' work to be done - the CIE only used male test subjects, and it's quite possible (nay, likely!) that women see colour slightly differently.

- Just for a bit of fun, xkcd.com did a quick study of the 'names of colours' - it's not really a good study of colour perception as every respondent was using their own computer screen of unknown colour rendering, but it is interesting!

 

EDIT - The xkcd results page may not be safe for work. I just noticed that there are some expletives in some of the respondent's answers.