Pexels.com,Sebastian Stam
LED lighting has some interesting attributes that have frustrated people ever since it was created. While some of those frustrations have eased, some still remain. For example, we know that LED lighting can dim – those LED PAR lights you hung over your client's stage dim nicely. But when they replaced all the light bulbs in their recessed can house lighting fixtures with LED flood light bulbs from the local hardware store, they dim down to a certain point and then "poof," they go from medium brightness to nothing, instantly. Or worse, go from black to 40% instantly, causing groans from the congregation.
So, what’s the deal here?
First, a note to fellow nerds or electrical engineers out there: this article is not intended to be part of Electronics 101. It's just the basics, and you may find it helpful to share with your clients.
One thing your clients should understand right off the bat: LEDs do not dim. Ever.
Part of the frustration lies in not understanding how LED lighting works. One thing your clients should understand right off the bat: LEDs do not dim. Ever. None of them. The way that LEDs work is that as DC voltage is applied across an LED emitter, there’s a threshold that gets reached. Once the voltage goes above this threshold, the LED emits light at full intensity. In other words, if you looked at a graph of light output vs voltage, it would not be a linear line – it would be a stair step.
How, then, do LED lighting fixtures "dim"?
For theatrical fixtures, there are electronics in the fixture that always receive power, and look at the control signal coming from the lighting console to determine how bright the fixture should be. It then blinks the LEDs very fast, so that your eyes average out the off times and the on times and see a lower level of light. The LEDs are blinking at thousands, even tens of thousands, of times per second—so fast your eyes can’t see the actual blinks. Depending on the speed at which they are blinking and the shutter speed of your clients' video cameras, the video camera may actually “see” the blinking, and that’s why you can get video that has LED lights flickering. This tends to happen on older and/or cheaper fixtures that don’t have as sophisticated control electronics in them; newer and better fixtures have a sophisticated enough design to avoid showing flickering on camera.
Now, in the case of replacing a standard light bulb in a house fixture with an LED bulb, it’s a similar situation but without the control signal. The electronics are powered by the voltage being applied to the socket by the room's dimming system. When it sees the line voltage dropping, say from 120v to 60v, the electronics blink the LEDs to simulate the light bulb dimming, much like in the theatrical fixtures. However, at some point, the line voltage to the bulb (and thus the electronics) will drop below the point at which the electronics can operate. Once the electronics shut down from being “starved” of voltage, it can no longer blink the LEDs, and the bulb turns off. Likewise, when dimming up, the line voltage has to get to a point where the electronics start working, and then it starts blinking the LEDs – jumping from off to 20%, 30%, or maybe even 40% instantly depending on the specific bulb.
This is also why there are dimming and non-dimming LED bulbs. The non-dimming bulbs are cheaper because they lack all the control electronics that blink the LEDs to achieve dimming.
And by the way, those 50,000-hour warranties on LED lighting fixtures? Make sure your clients know that, yes, the LEDs will probably last that long. However, the control electronics that blink the LEDs that aren’t covered by that 50,000 warranty—well, they might want to read the rest of the warranty….
