THE LED Conundrum

12207676 - a setting of light diodes, photographed at different stages of exposure to achieve this effect of detail in the light, that would be hidden otherwise

By Seth Waltz
Principal, AVL Designs

“Everybody says they wants LED theater lighting, yet we hear many people saying they have it and hate it. Totally believable because they got the wrong LEDs for their application.”

In the old days of analog lighting (meaning incandescent and halogen lights) lights pretty much turned on and off and up and down when you told them to. If you wanted to dim those lights there were a variety of devices that would dim them pretty well with the occasional lamp sing noise. (For those of you who don’t know what lamp sing is, it’s a buzzing of the filaments in the lamp that is audible as a buzz when the lights are dimming. Good dimmers don’t produce that noise, but cheap ones produce it in various forms,depending on the type.)

Thanks to flat-screen TVs we enter the wonderful world of LED lighting. Yes that’s right — television is at fault for LED lighting. Somebody realized that a nice flat screen display actually made colors and light all of the same time. That seemed like a good idea for lighting, which it is except that it also has a bunch of problems (what a surprise).

LED accomplishes a variety of things other types of lighting technology could only hope to do. Energy efficiency is one of those. About 25 percent of the energy for the same light output, but the best thing about LED is the ability to change color. Being able to pick any color of the spectrum without a gel being inserted in front of the fixture is really kind of spectacular. The problem is that getting the color requires a sophisticated array of LEDs and a driver which is basically a computer telling a variety of LEDs what to do (a room full of small computers).

Another problem with LEDs was how to get them to look like theatrical lights do. Most theatrical lighting uses lenses to provide focused tight beams of light. These beams of light have sharp edged capabilities that allow lighting designers to light just what they want and not have light spilling all over the place.

The first group of LED offerings couldn’t really do that because they were groups of individual LEDs that provided a wash of light, not a focused beam. (In the wash of light, there were also issues with the use of the individual color LEDs to create the lighting field so the whole thing wasn’t smooth and consistent.)

LEDs have come a long ways and some are just as good as traditional fixtures (not the cheaper ones).

Many specifiers select LEDs from catalogs, or the recommendations of manufacturers. LED should never be selected without actual experience with the specific product, and a full understanding of how they operate and are used in theater.

Some of the problems with LED lighting that were never issues with incandescent:

  • Color Rendering Index – Incandescent Quartz stage lighting has a high CRI in excess of 90. What his means in simple terms is your eyes like it as a white light source. Many LEDs have poor CRI , your eyes don’t like them.
  • Color Consistency – Pick a few LEDs from different manufacturers and check their red/green/blue base Led colors – they are not the same. This makes it impossible to get various fixtures to match when trying to create white or a specific color. (With some manufacturers pick two of the same fixture and they won’t even match)
  • White Light color Temperature – many LEDs do not have a good “white “period. When the red green blue base colors don’t work white doesn’t either.
  • Poor dimming
  • Stepping, flickering, etc.
  • Noise – Some LEDs have fans that kick on that are louder than HVAC noise.
  • Lack of light output  if you make the fans quiet. Many “quiet mode “ settings restrict light output  by as much as 50 percent.
  • High Frequency noise when dimming in some fixtures. A squeal or whine when dimming. Changes depending on the color selected.
  • Colors at the edge of light beams – “rainbowing”
  • Life spans that are much lower than expected – High output devices for theater are made possible  by overdriving the LEDs so they last much less than the 50,000 hours people expect. As low as 20,000.
  • Comparing data is not simple as many standards that do exist are not published by many manufacturers. You can’t compare what isn’t published.
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Summary — You have to test to select appropriate LED fixtures.

At AVL we test equipment and test fixtures extensively before we specify them. We test fan noise, dimming, color, rendering, dimming noise and overheat behavior. Based on those tests we will specify different fixtures for different projects based on budgets, needs, field conditions, etc.

Examples:

  • High fan noise isn’t a problem in mall, but is in a theater.
  • White not a big deal if I’m lighting in blue.

LED is a fast moving industry so we are testing fixtures regularly. The latest offering may or not be an improvement, and in some cases the latest and greatest have new issues that didn’t exist before.

LED Replacement Lamps and the dimming problem

What about just using LED lamp replacements? There are many “dimmable” LED replacement lamps on the market. You would think if it fits in the socket and says it dims it will right ? Not so much. Here is a brief discussion….

Incandescent Dimming

  • Incandescent dimming has been  easy and for the most part reliable. Many dimmer types will dim an incandescent lamp pretty well.
  • The hope has been that LEDs would be better. That is not the case.

Dimming of LED fixtures or Lamps:

  • LED lamps are called thing like “dimmable” and “truly dimmable,” and “really dimmable”
  • Unfortunately, “dimmable” can mean many things. It may mean they will dim well, not dim well or not dim at all. Dimming can also shorten the LED lamps life if the drivers and the dimmer type are not compatible.
  • Any dimmable LED solution needs to be a designed solution. LEDs have solid-state drivers within the lamp or fixture, which need to be compatible with the type of dimmer being used. Dimmer types : ELV, MLV, SSR, TRIAC, SINE WAVE AND IGBT dimming are all options, but not all will properly dim a particular LED lamp or fixture or in some cases a particular quantity of LEDs on a circuit.

Data Control Dimming

  • Some Led fixtures  dim directly via DMX data, some with 0-10VDC (which has its own issues), some over DALI and other control schemes. These control schemes are more reliable where the fixture is self-dimming, but the solid-state driver circuit boards within the fixtures can be subject to damage from surges and low voltage.
  • In essence these driver boards are mini computers, which need to have protected power, and have their power fully shut off when not in use. If this is not done the fixture life may be shortened by data driver failure. This requires an additional layer of control in the form of remote control relays or switches to kill the power feeds when the fixtures are dimmed off.

There are also issues of LED consistency device to device. A row of LEDs where all but one dims well is  likely a bad LED lamp  not necessarily a bad dimmer. It may also be conductor resistance, a bad LED driver, phase reversal or a host of other issues.

Substitutes when dealing with LED’s cannot be simply a cut sheet saying a lamp or device is “dimmable.” Specific combinations of LEDs, quantities,  and dimming devices must have been tested as a system to verify they will actually work.

A well written on online resource that describes the issues of LED Lamp dimming is available here.

The department of energy has authored this, as they recognize the issues moving forward.

Their basic recommendation is not to use any design without a mock up. Therefore when a contractor wants to substitute a lamp for a specified LED they will need to verify with the manufacturer that they have test data to support the dimming of the lamp in the configuration on the plans with the dimmer types and curve being used.

At AVL, we keep dimmers in our office and test lamps we might specify as replacements.

Seth Waltz is an acoustical consultant and principal at AVL Designs. Find Seth on LinkedIn here and AVL online here or on Twitter @avldesignsInc.

This blog was reprinted with permission from Seth Waltz and originally appeared here.

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