LED For Galleries And Museums

LED For Galleries And Museums

ETC have just released the Desire D22 LED wash light. This high quality LED wash has all of the features and colour rendering capabilities that museum and gallery applications require. It may be small, but it packs a punch. With 22 Luxeon® Rebel LED emitters, the budget-friendly D22 offers efficient ETC Desire®-quality lighting in a small 20cm footprint weighing less than 3kgs.

ETC Desire D22Tapping into the power of the x7 Color System™, which combines up to seven LED colours onto one unit, the D22 comes in three arrays: Studio Daylight, Studio Tungsten and Lustr®+. Using cool-white LED emitters, the Daylight version emulates natural sunlight, with a colour temperature of 5,600K. At 3,200K, the Tungsten model can replace less-efficient conventional luminaires for warm-white light. Lustr+ is the most flexible array, providing nearly limitless colour possibilities, from adjustable whites and subtle tints to vibrant, bold colours sure to make an impact in any installation. The D22 is available in three installation types: a portable version, a canopy-mount design, and a 3-circuit track-mounted model.

The D22 features a handy Desire-style user interface that lets you customise its functionality to fit any lighting task. RDM capability means you can adjust the luminaireís settings from any RDM controller, such as an ETC control desk. Or the D22ís Stand Alone mode lets you recall up to 32 presets and one sequence from the user interface, without the use of a desk. The D22 can be used wherever larger fixtures canít go, providing professional-quality wash lighting for art galleries, lobbies, museums and more.

So following the release of this fantastic fixture: here is a recap as to the importance in choosing a high quality LED fitting, like the ETC D22.

With the recent advancements in LED technology it is now possible for Museums and Galleries to make the change to LED fixtures without a large sacrifice in performance. LED offers obvious benefits for galleries and museums in the areas of efficiency and lowering maintenance costs but in order for these savings to be made the LED must address the specific performance needs of any gallery and museum. An artwork or an artefact is a fragile, sensitive and important object and therefore must be lit with a source that not only brings out the full natural characteristics of the object but protects the object from degradation. Previously, LED source wasn't capable of achieving this and therefore there was no replacement for the traditional Tungsten Halogen, but now by keeping in mind a few important concepts with regards to colour rendering and colour spectrum and with the progression of LED technology especially with regards to white LED's they are now a viable alternative to the traditional Museum/Gallery fitting.

As a result of the solid state manufacturing of light the spectrum of a white LED is much more limited than its tungsten halogen counterpart. The white LED is produced by coating a blue LED in a phosphor coating so it glows white. Obviously this way of manufacturing white light can't contain all of the colour spectrum so in order to fill out the spectrum the manufacturers add small amounts of red green and blue LED to the white diode array. This slightly fills out the spectrum but the white LED can still contain large gaps in achievable colours. These gaps can wreak havoc for real life rendering of lit objects. When we light an object with white light the colours that we are seeing from that object are the reflected part of that white light's spectrum. So if we light an object with a limited spectrum white LED then we can be missing a huge number of complex colours that will appear duller and more "gray" because of the limitations in the LED. This is particularly harmful in a museum/gallery situation where the complexity of the artefacts require "true to life" colour rendering, imagine viewing Jackson Pollack under a bad LED light... It may look something like this:

Figure 1 - Original Jackson Pollack    Figure 2 - Jackson Pollack Impression
Figure 1 Original Jackson Pollack                                                  Figure 2 What it could look like under a limited spectrum 
                                                                                                               LED (Impression Only)

If we are to speak of this concept technically, we would be referring to both the colour temperature of the LED in relation to the Black Body Locus, and this colour temperatures ability to render real life colours, the colour rendering index (CRI). The Black Body Locus is the path that the colour of a Black Body takes as the temperature of that body changes, therefore it is the benchmark that LED colour temperatures are tested against, think of it as the true white colour line. The locus ranges from Full Red at low temperatures through orange, yellow and up to bluish white at high temperatures. I have been speaking before in relation to a Tungsten Halogen fitting and a similar colour temperature LED replacement. We always need to compare apples with apples, like with like. So, if we are replacing a Tungsten Halogen fixture that normally burns at 3000K with an LED fixture we would need to compare the correlated colour temperature of the LED fixture against the benchmark Black Body Locus for 3000K, shown here as the black line. A stated LED colour temperature is always a correlated colour temperature, because as I stated before a white LED isn't perfect and it contains chromaticity variations and spikes in certain colour ranges and therefore requires LED manufacturers to make a correlation to the Black Body Locus to state a colour temperature.  The closer to the Black Body Locus at the 3000K point the closer to an "ideal' result for the fixture. This may sound very confusing at first but it is important to realise that the LED although stating a colour temperature of 3000K is not a perfect tungsten temperature although it may look close to the naked eye once you try and render colour on an object you may see an unexpected result due to the spikes and valleys in the spectrum.


The measurement of real life colour rendering is quantified by the CRI (Colour Rendering Index) of a fixture. The CRI refers to a light sources ability to render colours when shone at a series of real world test colours spread across the spectrum compared against a Black Body Locus source (3000K). The fixtures are then given an average score based on how they perform the rendering, with 100 being the best and below this being less so e.g. Natural Sunlight has a CRI of 100 while low pressure sodium has a CRI of -47. The CRI measurement however should be used as an indicator only as it is fraught with errors. The CRI is an average measurement so a fixture can have large gaps in the yellow spectrum yet still perform well on the blues and reds (LED's Sweet spot) and still maintain a high CRI although it misses a large part of the spectrum. CRI is also a computational measure, that is it is a formulaic measurement of the fixtures ability to render colour and the fixtures themselves are never actually shone directly at the colours, therefore can be weighted by the manufacturer. This sounds all doom and gloom but the point to be made here is that there is no substitute for real world testing of a fixture as the measurement devices can be weighted in any direction, but the CRI measurement does allow you to find a fixture that may work for you without having to trawl through the glut of fixtures and test everyone yourself. Also you can probably make the assumption that if a manufacturer doesn't mention a CRI in its marketing, it probably hasn't achieved a very good one, and might not be the best fixture for a highly specific Gallery/Museum Market.

All is not lost though as there are manufacturers that ensure their white LED's have the maximum possible spectral coverage. These are usually the dearer LED's as it takes precise measurement and calibration to get the right colour coverage, this is why if you need closer to life colour rendering it pays to fork out a little extra cash for a well manufactured LED product. For example the LED's used within the Source Four LED Tungsten are Philips Luxeon Rebel Bin 1 LED's which achieve a CRI of 98, plus in the below diagram you can see the region in which this bin performs against the Black Body Locus line. It is by looking for this information and selecting the correct LED fixture for the application you can now start making a real change to LED fixtures for all your Gallery/Museum Lighting needs, it is about being informed with the knowledge and using that knowledge to make the best decision.
BlackBody Locus PhilipsLuxeon 
Click here for more information on ETC's Source Four LED and other high quality LED products.

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