Mastering LED Lighting: The Art and Science of True Colour Rendering

In Partnership with CHAUVET Professional

From Source to Subject 

An overview of the colour science that determined the Ovation Rêve light engine design. 

When designing an LED luminaire for live and broadcast use, there are two main goals: brightness and light quality. These can also be competing goals. Achieving the highest output and the broadest light spectrum from the same fixture is challenging. It requires overcoming some issues with LED technology. These issues affect developers of professional luminaires intended for professional use. 

LED fixtures with multicolour light engines, as found in the Ovation Rêve family of luminaires, employ additive colour mixing to create tunable whites and a palette of colours. The quality of white light and the range of colours depend on the LED sources used in the light engine design. They also depend on software algorithms. They manage the complex task of combining multiple colour sources to produce a desired output. This output could be a true white at a chosen colour temperature, a deep purple, or a saturated pastel. 

Using the Rêve RGBAM (Red-Green-Blue-Amber-Mint) LED array as our guide, we will explore the benefits and limitations of each colour source. We will also explain the terms Green Shift and Red Shift in the context of multicolour LED lights. 

RGB (Red-Green-Blue)  

The familiar Red-Green-Blue configuration is common at this point, so we will treat RGB as one component of this light engine. RGB colour mixing was a welcome advance for many uses. It moved us away from traditional subtractive colour systems. This eliminated the need for gels, allowed native colour mixing, and led to cooler-running fixtures. But, RGB alone leaves gaps in the colour spectrum. It has spikes around the narrow wavelengths of its three primary colours.  

Ford Sellers, Senior Manager for Product Development at Chauvet Professional, describes a hypothetical scenario. It introduces the concept of colour rendering. It also explains why RGB-only LED light engines can be inadequate for applications that require accurate colour rendering. 

“When someone is looking at an object (a painting, for instance) the colours that they see are not being generated by the paint in the picture – the colour is being reflected by the paint. For instance, if you are looking at Van Gogh’s Starry Night, you are seeing a lot of blues. This isn’t because the painting is making blue light, but because the paint is actually absorbing all of the colours except blue and reflecting the blue light back at your eye.  Now imagine viewing that painting under a light that did not have blue in its spectrum. There would be very little reflected light and the painting would look mostly dull black. The issue with colour-phosphor based lighting (like LED) is that the colours generated by the LEDs are very specific.”  

Although Red, Green, and Blue are the primary colours of light, mixing RGB LEDs falls short both in colour rendering and colour production. Their hues lack saturation and appear dull, like the poorly-lit Van Gogh painting in Ford's example. 

A (Amber)  

Enter Amber.    

Mixing red and green produces an unsatisfying unsaturated amber-adjacent light.  Adding a native Amber source to the colour mix is what makes punchier pastels and warmer whites possible. Amber also combines well with Mint to enhance other shades of white. Amber LEDs have low output. So, their benefits are not seen unless a light engine's design includes enough Amber sources. Counting the Amber LEDs in the Ovation Rêve E-3 shows this. The Rêve light engine's design addresses this reality: 12 Red, 19 Green, 3 Blue, 9 Royal Blue, 24 Amber, and 24 Mint.    

RB (Royal Blue)  

If you checked the LEDs in the Rêve E-3 source array, you may have noticed an unexpected colour: Royal Blue. RGB is limited in its colour rendering and producing. This is true regardless of the quality of the Red, Green, and Blue LEDs. With blue, there is more than one blue to choose from when designing an LED array.    

Royal Blue is lighter and more vibrant than the Indigo shade of blue with which it is often confused. The Royal Blue wavelength adds visual pop to the colour mix. It works well with red and green sources to expand the colour range. Royal Blue also improves illuminated red and blue objects. It helps mix convincing shades of purple, cyan, and turquoise. It can also boost white light at warmer temperatures.   

It remains accurate to describe the Ovation Rêve light engine as an RGBAM system. Rêve luminaires with two Blue sources use firmware algorithms. They work in the background to deliver the benefits of Royal Blue without needing a sixth DMX colour channel.   

M (Mint)    

The Rêve E-3 array has more green LEDs than red and blue ones. Those familiar with RGBW fixtures may suspect why, based on their experience. RGBW systems can produce a too-blue white light when mixing colors. This happens because their efficient blue sources can overpower the green.  

The human eye links green with brightness. For apps needing high output and a broad spectrum, adding more green LEDs to a color-mixing system yields diminishing returns. Green LEDs have a narrow spectral distribution. This gives them a low colour rendering index (CRI). They also produce unsaturated green hues. These issues challenge developers of professional lighting fixtures. They want to accurately light performers' skin and costumes, along with stage elements, studios, and film sets.     

The solution comes in the form of Mint. As an LED source, Mint shares traits with blue LEDs. It is much more efficient than a green LED. Mint provides higher luminous flux at a given current. It also has a broader spectrum, improving color rendering, putting CRI scores above 90 within reach. Mint also combines well with green, amber, and red LEDs. It expands the usable colours to match those from gel filters in subtractive systems. It also offers new ways to produce white light.                 

In an RGBAM colour mixing system, Mint is key. It boosts lumen output, improves efficacy, and delivers the widest range of saturated colours. It also achieves the highest quality broad spectrum light.  

The other G:  Green Shift  

Green is magenta’s complementary colour and when combined will produce white light. Colour temperature (CCT) is key for lighting professionals. But, it does not fully cover the effects of the green-magenta axis on light's colour. In subtractive lighting, a Plus Green gel can mimic a fluorescent light. A Minus Green gel can filter out the green of a fluorescent light. It will match incandescent lighting better.  

In additive LED colour mixing systems, firmware-level software enables these adjustments. It translates to user-selectable settings for +/- Green as a DMX value.        

And a final T:  Tungsten emulation, otherwise known as Red Shift  

Much of the visual drama of entertainment lighting occurs at the lowest dimming levels. LED technology poses a challenge. Its dimming can look too digital compared to the warmth of traditional tungsten sources. This is a concern when matching LEDs with incandescent fixtures in the same rig. Like Green Shift, Red Shift is a solution of algorithms. They manage the complexity of combining colour sources. This lets operators simulate tungsten dimming with a simple DMX setting.       

For more information on LED lighting and upgrading your venue's lighting email hello@stage-electrics.co.uk