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LED A-19 and PAR Screw-In Replacement Bulbs

Bulletin Number: 165
Released By: Jim Fackert
Product Family: Dimmers
Date: 5/31/2018
Classification: LEDs

Stage and studio dimmers generally use “forward” phase controlled or “phase cut” dimming, and are designed for dimming incandescent lamps. LED lamps for stage and studio generally have internal power supplies and dimming, controlled via DMX and do not require external dimmers.

In some installations, dimmers are used to dim house lighting fixtures that have screw-in A19 or PAR incandescent bulbs. With the prominence of led based replacements for these bulbs and their energy saving and longer life, it is tempting to replace these incandescents with “LEDs”. This is not as easy as it looks, and should not be attempted without careful experimentation and research. See the references below if you really want to research this further. You are on your own!


First, there are issues with the appearance of objects illuminated with “LEDs”. Different and inconsistent color temperatures and color rendering make many of these bulbs unsightly in architectural installations. They must be chosen carefully.

Second, even though many models are claimed to be “dimmable”, there are issues with LED dimmability. Some are dimmable only with specialized dimmers designed for LED bulbs. Most are not dimmable over the full range of light output, and many do not dim smoothly or consistently. Unlike incandescents, there are no power line dimmable LED bulbs that dim smoothly down to zero light output as the power line is reduced to zero voltage. Because they have internal electronic circuits they inevitably must have a reasonable percentage of power line voltage to start to function at all. This means that LED bulbs cannot begin to generate light output until the power line reaches 20 to 50% of full. The best LED units dim smoothly up from zero beginning at a consistent power line level, but many do not, and so there is significant inconsistency in their startup level and significant issues with flicker or other misbehavior. To make matters worse, they present inconsistent and non-linear loads to the dimmers. This makes many phase controlled dimmers misbehave as well. Some people have had some improvement by leaving one or more incandescent lamps in a group of fixtures, to present a “normal” load to the dimmer. This does not solve the dimming range issues however.

Setting up a special dimming curve in the dimmer or console so that outputs “hop” to a significant percentage as soon as they are faded up from zero, then fade smoothly the rest of the way up can be a workable solution but will take some work to implement! Curves designed to dim fluorescents may work for this.

If smooth and consistent dimming is required in your application, stick to incandescents, possibly converting to halogen incandescents for power savings.

Another option would be to convert to LED lamps that operate on un-dimmed power, and use wireless control protocol such as Zigbee Lighting, WIFI, etc. to make them dim smoothly. Control of color and of individual lamps that are on the same circuit can be a bonus if you do this.

We would love to hear about any successful use of LED bulbs in phase controlled dimming. LED bulbs are improving all the time, and manufacturers are working to make replacement of incandescents painless, but it is a difficult quest.

References on the web:

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