LEDs

[RobertKendall]

Things that may interest?

 

http://www.pixelpar.com/pixelrange/default.aspx

http://www.martin.com/product/product.asp?product=stagebar54

http://www.pulsarlight.com/ChromaRange.htm

http://www.mushroomevents.co.uk/

 

 

Good Luck :)

[DavidLee]

Surely RGB is all you need for any form of full colour full spectrum light..like the phosphors on a TV.

For coloured LIGHT you are correct and RGB mixing is great for projecting images or washing plain backcloths. However the problems start when you want to use the light to illuminate a coloured object.

 

Your eyes have only three colour sensors - red, green and blue - with very broad and overlapping spectra and it's the relative strength of the excitation of the three sensors that determine the colour you see. Yellow light (for example) will excite both the red and green sensors and give you a sensation of seeing a yellow colour. If you mix monochromatic red and green light - as from an LED colour changer - in just the right proportions to give the same balance of excitation of your red and green sensors then you will see exactly the same yellow colour of light.

 

However the light does not actually contain any yellow frequencies at all - only red and green - so if you try to use it to illuminate a pure yellow object (ie one that reflects only yellow frequencies) all the light will be absorbed and nothing reflected and the object will appear dull and dark.

 

Try it with some yellow textile and compare the effect when lit with red/green and yellow gelled lanterns.

 

David

[Tomo]

Your eyes have only three colour sensors - red, green and blue

No, they don't.

There are four sensors in an individual with 'normal' colour vision, and their colours are Blue-Violet, Turquiose (rods), Green and Yellow.

 

(Weird, eh?)

 

The Turquiose, Green and Yellow sensors have extremely wide bands, so the peaks are not distinct.

Blue-Violet is much narrower and doesn't overlap with G and Y much, but does with Turquoise.

 

Turquoise is shoved to near maximum in daylight, so doesn't play much of a role in bright light, and becomes much more important as the light dims.

- This is why everything looks a bit 'blue' at night, and why we use a blue tint to indicate night in TV and theatre.

 

The main reason for there being no magenta LEDs is because it isn't actually a particular light wavelength - it's an appearance of a mixed colour along the "Line of purples" at the bottom-right of the CIE diagram.

So you can only get it by mixing different light wavelengths together - 380nm (deep violet) mixed with 700nm (red) has a gamut along the entire length of the line of purples, and could make a good magenta.

- you won't see these in a real fixture though, as the "Green",

 

RGB light sources (eg displays) work because of the way the G and Y sensors overlap and are processed - the overlap is used to determine the brightness AND wavelength of the incident light.

- If you look at the CIE 1931 diagram you can see how this works.

 

David is correct about reflected light though - an RGB parcan produces very narrow bands of Red, Green and Blue light, so something with narrowband reflectivity would appear dim.

- More disturbingly, something that reflects light outside these, but also within these colours can completely change colour.

 

For example, you have an item that has two narrow reflectivity peaks - 470nm (deep blue) and 580nm (yellow), and looks orangey-purple under tungsten and sunlight.

Stick it under an RGB parcan, and it would appear dark blue!

[musht]

if I bought an LED par can, it would last ages, but eventually some of the LEDs would start to go off colour or just die; Could I then replace individual LEDs in a par? or would I just have to chuck it and buy a new one?

 

Entirely feasible to replace individual LEDs, depoending on how close to original or matching with others it needs to be.

 

Courtesy of Clive Mitchell, www.bigclive.com , a less than year old clock at a major railway station, from a few years ago. Sometimes its worth spending that bit more......

 

http://www.emanator.demon.co.uk/crapleds.jpg

[DavidLee]

Your eyes have only three colour sensors - red, green and blue

No, they don't.

There are four sensors in an individual with 'normal' colour vision, and their colours are Blue-Violet, Turquiose (rods), Green and Yellow.

To enter panto mode - Oh yes they do!

 

Monochromatic Rods play little or no part in colour vision - they are much more sensitive than the cones and are very much more numerous but they are wired together in clumps and so have grossly inferior acuity. They also have a very much slower response and crucially are not present in the fovea and so make no contribution to detailed vision.

 

Thus there are three varieties of colour sensors used in "normal" colour vision - the cone cells. The long wavelength sensor - the L-cone is generally known as the Red receptor because it is entirely responsible for perception of red light even though its peak response lies in the yellow region of the spectrum. Indeed there is not much difference between the spectral response of the red and green cones and their spectra are closely overlapped with peak separation of only about 30nm compared to a peak separation of about 110nm between the green and the blue cones.

 

Whilst normal colour vision uses three cone sensors there are genetic abnormalities. A significant number of people (mainly men) have only two effective sensors - most commonly resulting in red-green colour blindness - and there is some recent evidence that up to 10% of women may possess cones with 4 spectral ranges. Other species have many more - tropical fish and birds frequently use 4 or 5 receptors and the Mantis Shrimp has vision based on about a dozen types of cone cells. At the other end of the scale most non-primate mammals use only two and marine mammals generally only have a single cone receptor and hence have no volour vision at all.

 

David

 

Edited to remove an irritating rogue apostrophe!

[whitehousejamie]

Anyone know the price to buy these units, and whether there is a UK distributor?...

 

http://www.movingled.us/IMG_0106_1024.jpg

 

Pretty sure Butlins is now playing with a few of them.

[smalljoshua]

Anyone know the price to buy these units, and whether there is a UK distributor?...

 

http://www.movingled.us/IMG_0106_1024.jpg

 

Pretty sure Butlins is now playing with a few of them.

Not exactly the same but similar Vari-Led from Thomann About £2000

[IanR]

The MovingLED information is available here http://www.mlt.gb.com, we sell it.

Current UK List Price is £2520 Ex Vat.

Butlins Currently have over 70+ Units which (fingers crossed) have all been very reliable. (Im biased though!!)

If anybody would like to see one in action give me a shout!

[andyc]

Just to add a little here about the cost issues associated with high quality LED fixtures. Most high end use the Luxeon led which is of a particular process and technology. Due to the manufacturing process each led comes off the production line with a slightly varying wavelength, color temperature from a fixed voltage curve. Because of this the led's need to be sorted into batches of similarity within a tolerance which is a process known as binning. Combined with expense of individual high quality led's and the actual process of "binning" contributes to the expense of led fixtures.

 

Andy