Dimming of LEDs

Dimming of LEDs can be confusing because there are several ways to dim and many different products for each method. Using the wrong products together can cause many issues.

When you think of dimming you probably think of slider-type controls mounted in the wall, like those by Lutron or Leviton, found in most homes and offices. But it’s not the only way.

They are “triac-based” dimmers, though you won’t see those words on the package. They work by chopping the 120 volt AC power signal, which basically reduces the amount of power getting to the light.
Traditional incandescent bulbs with tungsten filaments dimmed very easily by this method. However, LED lights are electronic devices, more complex than an incandescent bulb.

LED lights can come in different forms. They might be bulb-shaped with a screw base, designed to replace traditional bulbs in lamps and light fixtures. They might be linear flexible strips that are used for under-cabinet and cove lighting and many other effects. They might be “LED bars” which are similar to LED strips but in a rigid form. They could also be “LED panel” lights designed to replace fluorescent fixtures in offices.

LED screw-in bulbs are generally designed to work with wall-slider dimmers. However because the electronics inside each company’s bulb are a bit different, they may work better with some dimmers than others.

That’s a subject for another article.

Each bulb has a built-in power supply (“driver”) that converts the 120 volt AC wall power into a lower-voltage DC power to power the LEDs. That built-in driver is also responsible for converting the “chopped” AC power from the wall dimmer into a lower light output.

LED flexible strips generally rely on a separate power supply / driver to convert the 120 V AC wall power into the lower voltage suitable for LEDs. Can these be dimmed the same way, with a common wall-dimmer?

The answer is, it depends. If you use a “triac dimmable” power supply (driver), the answer is yes.

But is it the only way? No. You can use a non-dimmable power supply, and add a separate low-voltage dimming module to the 12 v or 24 V DC output to dim the output side, often using a PWM (pulse width modulation) technology.

These dimmers may include a knob, buttons or slider to set the dimming level. Some are available with a remote control so you can put the control on the wall or carry it with you, within a certain distance range. They can communicate with the dimming module by infrared (IR) light similar to a TV remote, or by radio-frequency (RF) signal.

But wait, there’s more!

There are drivers (power supplies) on the market that support 0-10 volt dimming, and other methods. What’s that?

For 0-10 volt dimming, a separate pair of low-voltage wires must be run from a special 0-10 volt dimmer to the LED driver. That seems like a lot of extra work, and it is. Why does this even exist? Basically it wasn’t that easy to design a high-power “triac” type driver, so this system was developed. It’s commonly found on drivers for LED panel lights, warehouse-type high-bay lights, but other lights might use it too. Note: some automation systems such as Lutron RA2, Vantage etc. offer modules that support 0-10 volt dimmable power supplies. However, they also offer modules for “normal” incandescent or LED screw-base bulbs – those are the modules sthat hould be used for “triac (AC) dimmable” LED power supplies (drivers).

You can buy drivers that support 0-10 volt control signals, and connect them to power LED flexible strips and bars. BUT be careful: The connections on those drivers are often just marked “DIM”.

Do not connect a 120 volt AC wall dimmer to those inputs. It won’t dim, and may even damage the driver or dimmer. Why do they just put “DIM” then? Because some of these drivers can also accept a varying resistance as a dimming control on the DIM input. That’s normally supplied by a “potentiometer” (POT) which is like a knob on a stereo system, also found on things like electric guitars. So, technically this is a “dimmable” driver, but it’s not dimmable by the common wall sliders, only by more esoteric methods!

Seems weird? Maybe it’s weird for lighting, but these power supplies are also designed for industrial applications, not just residential lighting. And they may be used all over the world, where different types of controls may be more commonly used. There are even different control protocols such as DALI, Zigbee, Zwave and more that can be used to achieve dimming and other effects.

Having read this far, you might be more confused than ever.

Don’t worry, we’re here for you. Call us, or use the contact form on the website and ask us your specific lighting and dimming questions!

“Daylight” does not mean full spectrum

Often we hear people say that they are using “daylight” bulbs to light their studio workspaces because they want to see the colours accurately.

Unfortunately, this is generally a mistake, resulting from a simple misunderstanding of the terminology. Everyone knows that sunlight is a full-spectrum light source. We’ve all been taught than when looking at paint samples in a hardware store, it’s a good idea to take them outdoors to see the true color of the swatch. Or if you’re buying clothes, you might want to look at them under natural daylight.

So why are typical “daylight” bulbs a bad idea? Don’t we want a light source that’s as much like the sun as possible?

The short answer is yes, you DO want bulbs that provide full spectrum lighting, as the sun does. However, that’s not what “daylight” bulbs do!

The term “daylight” relates to the “colour temperature” of the light. That is, whether it’s a “warm-colour” or a “cool-colour” light.

“Warm” light mean yellowish light, and “cool” light means light that has more blue content. Incandescent light bulbs give off “warm light” that’s rather yellowish. Yes, those bulbs are also very HOT, but that’s not why it’s called warm light.

Sunlight has much more blue content, so it’s considered a “cool” colored light source (even though sunlight can be pretty hot too!)

So what’s the problem?

Your typical “daylight” bulb does have lots of blue spectrum, like the sun. BUT it doesn’t have enough red spectrum. Natural sunlight has both.

And what’s more, if you are using a fluorescent bulb as your “daylight” source, not only are you missing out on red spectrum, you’re missing a lot more too. Fluorescent lights are notorious for having many peaks and valleys in their light spectrum. Each one of those valleys is a weak spot in the spectrum. That’s bad.

Why?

Because all the colour you see is actually just reflected light! Grass looks green because it reflects the green spectrum of light. Its not really a green colour, it’s a green reflector.

And we’ve all been taught that black objects absorb light. Which is true … but it’s more accurate and useful to realize that objects look black because they absorb light. If it reflected some or all of the spectrum, it wouldn’t be black!

So “daylight” bulbs usually give you the bluish cast of sunlight, at the expense of the rest of the spectrum, which is vital. You can’t see paint colors properly (or clothing, furniture etc) if those colour are not fully present in your light source.

Take a green ball and shine a red light on it. What do you see? A red ball? No, it’s impossible. The red light is absorbed by the green ball. Instead you see a grey ball! That’s an extreme example of what happens when your light source doesn’t have the spectrum required to render colours accurately.

And if you are an artist trying to paint under a deficient light source, you might as well be working blind, because you really won’t be able to see what you are doing properly. Unless of course, all your works are only blue, then you might manage. But for the rest of us, a good full spectrum light source is the way to go.

The warmness / coolness of the light source is called the “colour temperature” or CCT. That’s what “daylight” is all about. It means it’s a “cool” light.

The spectral accuracy of the light source is something different. Its measured by the “colour rendering index” or CRI. With LEDs you can get full spectrum lights in virtually any colour temperature, including daylight. But most of the time, you don’t.

Most LED manufacturers sacrifice some colour rendering accuracy in order to make their lights brighter and more efficient. Sometimes that’s ok, and sometimes it’s not.

Lighting artwork is definitely one of those times when it’s not OK to sacrifice light quality!

In case it’s not obvious yet, at Lumicrest we specialize in full spectrum, High CRI LED lighting.