Dimming to Warmer CCT’s – On Second Thought

Posted: February 21, 2012 in Art and Design
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When LEDs first emerged, I was one of the many who expressed the opinion that a lighting system that could dim to a warmer CCT, imitating incandescent lamps, would be desirable. I want to take this opportunity to retract that original opinion and thought. I’ve played with it, seen the products available that do it, and have experimented with the approach… and can say unequivocally that I really don’t like it at all.

One of the problems with incandescent dimming has always been the patchwork of CCTs one gets through a space from different dimmer settings for the various products in a room. This has never been a good thing. Further, the change in CCT of an old school incandescent lamp is significantly different than halogen lamps, as it the character of the color. I for one have fallen out of love with the old incandescent lamp long ago. Over the last 20 some-odd years, I have come to use halogen sources over all incandescent forms, preferring the cleaner white color over that yellowy dinginess of the incandescent lamp. Incandescent lamps (non-halogen) produce a decidedly ugly color that I personally feel is misrepresented by their high CRI rating. The fact that the CRI formula will show a dimmed incandescent lamp with the same high CRI number, even when it very noticeably distorts color in a space, is a condemnation of our poor color performance metrics, not an indication of this lamps superior color performance.

Working with SSL has changed my views of colored light sources that distort color perception. I have come to find that having every light source producing the same color, at all light levels is far superior to the hodge podge of incandescent lamp colors, and much cleaner than the halogen lamp. I find the integrity of blues, greens and oranges, and the balance between them being maintained, even when the light levels are adjusted, much more pleasing than the odd yellowish haze that incandescent dimming creates, killing blues and amping up the reds disproportionately.

While it seems to be a cool innovation to force LEDs to move more and more to incandescent behavior, I feel the result is less attractive in real world application. That said, I will say also that the selection of colors used within a space must be made using the source what will be used in that space. With this, I contend that the results of selecting colors off surfaces, fabrics, carpet, etc… under a 3000K LED system, with at least 80CRI, can produce as warm a space as you desire. When dimmed, the color balance will not need to change at all, as you will have set that atmosphere with proper color selection. Overall, this will produce a far more attractive space, with less distortion of colors, including the skin tones of individuals occupying the space. Personally, having everyone in a room look as though they are on the liver transplant wait list when the lights are dimmed is hardly a good result of dimming.

On the other hand, if the colors were selected under incandescent lamps, then expect a significant difference in appearance under any other source, halogen or LED included. This is the primary issue with fluorescent lamp retrofitting. It creates a shift in light color character that was not anticipated when the space was originally designed with an incandescent light source. Of course it is not going to be as nice looking, it was not designed to work with the new light source. The same will occur with LED retrofits, simply because down-converting phosphors are weaker in reds and oranges, and stronger in the blue and green regions, than incandescent lamps, so the color will not be the same.

Now to the LED products themselves. I have seen several strategies for attaining the warming shift under dimming. One uses red-orange LEDs to simulate the yellow orange shift under dimming – which creates significantly more color distortion than incandescent lamps, due to the over-saturation of reds as the product was dimmed. Another uses a very warm white LED (2000K) and a warm 2800K LED to produce a marginal level of warming. Unfortunately the two together are only 70 CRI, and when dimmed drop to 65, so the color effect is really bad across the board. There are RGB systems as well, and when measured, most generate really poor CRI, often in the 35 to 45 CRI range, regardless of white mode, so color distortion is really bad and must be tested on the interiors involved. Another I tested uses RGB+A and another RGB+W, both create a wide range of whites with CRIs in the 80’s. However, they also cost a lot more, require complex controls and when one light is dimmed differently than those around it, the color differences between them became very noticeable and unattractive.  With some effort in fine tuning color balance, some of this could be reduced, but in the end, its not a clean approach.

Ideally, a dimming system would have two settings. Dim individual loads within a space to suit the mood. Color setting for the entire room to suit the desired color balance. In this case, I would operate in the 4000K down to 2800K zone, at 85+CRI no matter what color is selected. This can be done with DMX controls and complex luminaire designs. However, failing that, I have found that simply selecting a good LED to start with, at a CCT of around 3000K, and using that to select the colors in a space, with intensity control alone, leaving the color static, is the next best approach. I have come to believe that the desire for dimming to warmer CCT’s nothing more than our romance with the old incandescent technology, attributing its faults as a desirable feature. While the ability to dim an LED and not experience a significant color shift while maintaining proper color balance may not intuitively sound as good, in application it can be far better than what we experience with incandescent lamps, and blows the dim-to-green/blue of fluorescent lamps away completely.

Once you get used to it, and learn to look past it being different, re-appraisal of incandescent lamps will reveal just how ugly the color shifts really are under dimming. I contend that as time passes, we will look back at this and wonder just what were we thinking? For me, I have found the 2800K incandescent color to be unattractive overall as far too yellow orange, made truly bad using LED sources. After living under 3000K for some time now, and 4100K in my shop spaces, I no longer see the light source color around me. I have also done experiments where I temporarily re-lighted these spaces with the incandescent lamps that once served… and am taken aback at how dull everything appears, and how much the cooler surfaces and white materials are transformed from vibrant to dingy and washed out, with a pall of tan/brown over every surface in the space.

  1. PartyMan says:

    As a consumer, there is one function I wish I could achieve with LED lighting and that is “mood” lighting — either warm, dim light like for romantic dining, or party lighting which would also be on the dim side with flattering warm color. This is an application where it would not matter what decorating choices I made under 3K or 4K lighting, we can’t change the color of people’s faces to match the lighting, we have to change the lighting to make people feel attractive.

    • kwillmorth says:

      As I stated in the article, the issue is not with dimming to warmer tones, it;s with the dimming of a room with more than one source, resulting in a mish-mash of colors, which is not desirable. I proposed using a single CCT to get rid of the patchwork quilt of colors in a space. I also noted that a strategy where there could be two modes, a dimmed mode at a lower CCT, and a full bright mode, centered on a higher CCT – again getting rid of the patchwork. However, for me personally, I see nothing compelling in the argument that just because an incandescent lamp goes yellow when dimmed, that this represents a specific advantageous human visual effect. As noted, I personally have experimented with the concept, and have found that a better approach is to select a high CRI source of a warm enough CCT to provide the flattering effect, and not mess with the complexity and issues of mixing LED sources necessary to copy the failure of incandescent lamps to maintain color when dimmed. It’s obviously a subjective call.

  2. […] is an interesting opinion piece from Luminique SSL, discussing a point of view on the value of LED replacement lamps dimming to a warmer color […]