Color is so much stranger than it seems at first glance. When we were children learning red, green, yellow, orange, blue...it seemed so straightforward. So easy to get the right answer. When did you realize that it was all a sham? An illusion? For me it happened in high school when I always wore socks to match my shirt (yea 80's!) I bought a pair of royal blue socks - perfect - until I got them home under the incandescent light. They were purple. What? Okay, then, fine. I'll wear them with my purple shirt - until - I got to school and they were blue again. How mortifying. What had happened?
Notice the cool blue color temperature in the middle of the bottom row.
In the previous post we looked at the color temperature, or color of the light. That actually has little to do with color rendering, which is the color of the objects under the light. See the difference? Either a warm source like incandescent or a cool source like daylight can render the color of objects nearly perfectly (my socks were blue under both.) It has to do with how much of the pigment is reflected back to your eye by the light source.
The three pictures above subtly illustrate differences in color rendering (or color accuracy) on the apple. The apple is the same, but it appears more pink, orange, or deep red under different lights. In the picture on the right the yellows in the apple are easier to see; In the middle picture, the dark lowlights are well defined; The one on the left seems smooth in color - neither the lowlights nor the yellows are obvious. It is important to know not only whether a source is warm or cool (color temperature) but also how it renders the objects under its light (color rendering.)
The new Lighting Facts Label (at left) required on light bulbs (lamps) sold in the US lists the color of the light, but not its color accuracy. Another new label (below) uses both. As a consumer of today's complex lighting sources, you need to know both. The color accuracy scale goes to 100. In most cases, choose the highest number you can afford. Something in the 80s for fluorescent and close to 90 for LED. If you have the opportunity to try multiple sources to see how they look in your final application, that is even better. Check color accuracy to avoid disappointment and purple...no, blue...no, purple socks - or worse!
As a student at the University of Kansas I worked for the EADC - Energy Analysis and Diagnostic Center. This was a fantastic DOE-sponsored program (now called IAC) which employed college students to perform free energy audits of manufacturing plants and commercial office spaces and then provide them a report full of Energy Conservation Opportunities (ECOs.) One of our most common ECOs at that time was: replace existing T12 fluorescent lamps and magnetic ballasts with energy-saving T8 fluorescent lamps and new electronic ballasts. One of the added benefits of this upgrade was the elimination of "flicker." Though imperceptible to some, flicker can be quite problematic for sensitive individuals, causing headaches or even seizures. Flicker happens with the natural cycling of AC power, but with the higher frequency inherent in electronic ballasts, the fluorescent phosphors do not have time to dim, and therefore flicker is eliminated.
We had a handy tool that we could use to verify whether the existing ballasts were magnetic or electronic. It was a top, called a flicker checker. When you spin it under electronic ballasts, you see a series of concentric gray circles like in the first video below.
However, if the existing fixture had magnetic ballasts, the flicker checker displayed choppy squares instead of concentric circles, illustrated in the video below.
The thing is, this second video wasn't a top spinning under a fluorescent lamp with a magnetic ballast. It was spinning under a dimmed LED fixture! Once again we need to watch out for flicker in our lighting. The great news is that this time almost everyone is armed with their own personal flicker checker! No...maybe not a top. Pull out the camera on your phone and point it at the nearest LED source. If you see a series of bars or stripes on your display, the source is flickering. If not, then you have a high-quality LED with a compatible dimmer and/or driver.
Try it. Let us know what you find!
I have just returned from another Fabulous Las Vegas Lightfair - the biggest annual lighting trade show in the US. Three years ago I returned from Lightfair on a rampage. It seemed that everyone was showing off their "new" LED product, and every one of those products was failing at everything that matters to lighting designers: glare, color, flicker... Then last year I saw improvement. The story wasn't just, "hey we have LED" but rather, "our LED is better because of its color" and "we have improved the optics by..." Thank goodness the manufacturers have continued this trend. There were some LED products that actually made me hopeful. BUT...
This year my favorite question to ask became, "What do you mean by that?"
I was repeatedly told, "Our LED fixture is fully dimmable." If someone says something is fully dimmable, I think that should mean FULLY dimmable, as in it can dim from zero to 100% without flickering and can be switched on or off at any point along that dimming curve without flickering. We are NOT there yet, folks. None of the products I saw had that capability. None of them. But I was told at least 20 times that various products were fully dimmable.
What does that mean?
Sometimes they meant the product would dim down to only 10% before turning itself off or beginning to flicker. In the best case scenario they meant it would dim to 1% and then off. I know that is close to full dimming and most of the time that is good enough. But that is fluorescent dimming at its best. That is not equivalent to incandescent dimming. The language with fluorescent dimming has always been 10%, 5%, 1%. I don't recall it being described as fully dimmable. I don't think LED should be described as fully dimmable yet, either. But I am still hopeful it will get there. Don't settle for less. And don't forget to ask, "What do you mean by that?" until fully dimmable truly means fully dimmable!
Lisa J. Reed, lighting designer and Principal at Envision Lighting Design, LLC