Not So Easily LED

I keep hearing that the incandescent light source is dead – a light source that’s shuffled off this mortal coiled-coil. But I wonder if perhaps we are being actually being let down by our lighting manufacturers.

Is LED technology really that close to replacing traditional incandescent light bulbs that we can walk away from an attachment we’ve had with hot glowing things since man first stumbled across fire? An emotional connection we’ve had since well before the invention of the wheel, before even sliced bread?

Is it concerning that our manufacturers are abandoning incandescent sources in favour or LED technology, or is it yet another case of the unstoppable march of Technology. As the compact disc was to the vinyl microgroove record, will we slowly see the quality of our ‘tools’ degraded in the name of progress?

PLAYING WITH FIRE

Humanity’s affection for fire is deeply embedded in our DNA. Most people can spend hours staring into a fire or looking at a candle in some sort of mesmerised state. The very essence of our connection to incandescent light sources arises from those same feelings, albeit that an electrically-heated tungsten wire is lot more stable and controllable than a naked flame. We are drawn to it like the animals that we are.

I’ve never seen someone enamoured by the sensation of an LED source. Sure people get excited at the energy efficiency, technology and possibilities that LEDs present, but we don’t have that built-in resonance a simple 60W lamp can evoke. Like watching a fire, one can watch an incandescent lamp heat up and emit light with wonder. The characteristics the globe takes on as the filament heats and cools bring a similar complexity, dynamic flow and rich range of spectral colours that we see in fire. That sort of visual journey just doesn’t exist with an LED source. At least not at anything approaching a practical cost, and even then, not without some outboard processing. 

KELVINS AIN’T KELVINS

The big problem is that LED source manufacturers are so caught up in getting an LED source to look convincingly like a tungsten source at 2800 to 3200K they’ve overlooked that many of us actually use the variations of colour along the tungsten dimming curve as part of the palette for our art. Not just in shows or on camera either, but in our lounge rooms and offices. My hallway has expensive LED downlights that dim: great. However, when they dim, I don’t get that same warmth I have in my lounge room when those venerable incandescent globes are dimmed. Sure, my hall is darker when I dim it, but the mood barely shifts. Unless I want to go to the effort of colour mixing RGBAW LEDs in my hall to simulate that colour (but even then, not the colour rendering), I’m not going to recreate that feel. Certainly not in an efficient way that doesn’t make me look like the lighting geek that I may be.

So, are we just romanticising the incandescent sources, or is there some technical logic behind the Don’t Make Me Stop Using Incandescent Light movement? Let’s begin with the colour spectrum. An incandescent lamp by its very nature as a hot glowing object emits the full visible colour spectrum in varying amounts, which is what the colour temperature scale measures. By definition, an incandescent source has a Colour Rendering Index (CRI) of 100 because it can reflect off (render) every colour present in an object it is illuminating. During a fade up or down of a tungsten source, while the relative mix of the spectral colours may vary (colour temperature shift), the whole visible spectrum is still being emitted.

Every non-incandescent type of light source such as fluorescents, metal halides, and especially LEDs, produce their light by some physical principle other than simply heating something up, and consequently don’t produce the entire colour spectrum in ‘natural’ proportions. Most of these sources are substantially more efficient at producing light than incandescence due to heating, but to make them useful for tasks such as viewing coloured objects like people, artworks, full-colour images, and food, we have to resort to various tricks to approximate the light that our brains have evolved to see. The CRI of a light source is an attempt to measure how well those tricks work. 

Any LED, even one with a relatively-good CRI, may have obvious spikes and troughs in its output spectrum. Whilst some of these shortcomings may not be very noticeable to the human eye because our brain compensates for them, they are often quite obvious on camera where the film or the sensor chip can’t be as easily fooled. To make matters worse, LEDs often vary in colour output between manufacturing batches, even on the same model of light, depending on the batch they were sourced from and when they were purchased. 

NEVER MIND THE EMOTIONS: FEEL THE TECH

Then there are the technical aspects of LED application. Take for example a community theatre group. Perhaps they have 16 luminaires to play with – a mixture of incandescent fresnels and profiles. If the local council gives them a grant to buy six new high-efficiency fixtures using a source such as LED (that has a constant colour temperature, rather than the varying colour of an incandescent lamp on a dimmer), will those new sources sit equally among the others? It’s likely they will be so different that those new fixtures will always need to perform exclusive duties so they don’t stand out as being different types of lights.

Let’s shift perspective and look at a video production studio. Is it possible to blend new light sources that not only have a different control system (internal dimming control as opposed to traditional external dimmer control) but also have drastically different colour temperatures across the dimming spectrum? Well, in a pinch, sure they can. However, the question arises, does your average studio want to spend hours a week shuffling different sources around the grid to perform the same jobs? Do they want to sacrifice the ability to re-purpose a light on a whim? Not really.