What is colour shift?
Colour shift is a deviation from the originally selected colour which happens on the LED chip. Generally, this shift usually goes to the blue end of the spectrum – so you lose the spectrum outside of the blue emissions. However, this deviation can affect green and red emissions too. Different chips will deviate to a different colour depending on the characteristics of the phosphorus used in the LED chip.
Perhaps the easiest way to think of colour shift is that it’s effectively lumen depreciation in specific parts of the LED’s colour spectrum.
Why does it happen?
Colour shift can happen for a number of reasons.
One of the most common is caused by defects in the chip during the production of the LED. Another reason is due to a problem with the application of the chip’s phosphors coating. This coating converts the invisible, pure UV emissions into visible light and can change its characteristics over its lifetime.
The biggest cause though is nothing to do with the chip itself but is due to its misuse by the luminaire manufacturer. This can be because:
- They’ve mounted the chip on the board incorrectly.
- They’re driving the LED too hard beyond its effective design parameters.
- Or, because of luminaire design issues, it isn’t being cooled sufficiently.
How do you recognise it?
Easily. You can see it with the human eye and measure it with the right equipment, such as a spectroradiometer. The extent to which you can recognise it – by sight or measurement – depends on how bad the colour shift is. This in turn can depend on how poor the product quality is, or how much the chip is being overheated. Either way, a rapid colour shift will usually result in the complete failure of the LED board in a very short time.
How can you prevent it?
A good place to start is chip selection. Using the right chip for the required application will help stop any colour shift. So, when you choose this crucial part of your luminaire you need to assess its lifetime depreciation by looking at its LM80 data. This will give you a good guide as to how a chip will age. You can find out more about LM80 here.
Also, make sure the PCB board manufacture has good quality assurance systems in place and follows the chip manufacturer’s mounting instructions to the letter.
The best way to prevent it however is by putting extra care into the heat management of the luminaire. A well cooled, quality LED, even if it’s being driven by high currents, will rarely suffer from colour shift. This is why when we’re developing a new product, we always put heat management at the top of our key considerations – unlike some companies we won’t mention.
How does it differ from lumen depreciation?
General lumen depreciation is where the total light emission decreases across the whole spectrum. And, as we’ve already said, colour shift is in a way is lumen depreciation that happens more in certain parts of the spectrum. For example, a shift to blue just means you’re losing more flux from the rest of the spectrum and not an increase in the blue area.
Does it affect all the luminaires in the same location in the same way?
It depends on the cause of the shift. If it’s due to a production defect, the luminaires may be affected in different ways in the same location.
If it’s a result of poor heat management or poor chip choice, then all the luminaires in the same location will be affected in the same way.
Does it only concern high-temperature climates?
No. But it is more likely to happen in them because the high working temperatures will cause it to happen faster. A light that may show colour shift in Finland will almost certainly suffer from it in Qatar. So high-temperature climates in a way are the ultimate test in terms of quality and heat management.
Paolo Corno, Technical Director & Co-Founder, Midstream Lighting
With over ten years of LED lighting industry experience, Paolo is an invaluable and highly regarded member of our core leadership team.
Coming on board as one of the company’s co-founders in 2013, Paolo’s responsible for overseeing our Lighting Design, Engineering, and R&D Teams. He personally leads the design and development of Midstream’s comprehensive product portfolio – including the Atlas, Titan and Modus Floodlight Series – which are installed in over 85 airports globally.
An experienced designer, who holds a degree from Bocconi University in Milan, Paolo has led the design of over 100 LED lighting solutions in the aviation, maritime, sports and horticultural markets. ensuring that all national, local, industry and customer requirements are met.
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March 11, 2021