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We tried upgrading our old scoreboard in the gym with LED bulbs and now they flicker rapidly. Is there a way to fix this? There are close to 200 bulbs on the scoreboard that were previously 7w bulbs.

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    Can you give any info about the make/model of the scoreboard? We'll be able to generate much better answers if we can look up details about how that specific board works. Knowing the make and model of your LED bulbs might help as well.
    – bta
    Mar 7 at 0:00
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    I’m voting to close this question because it's not about home improvement.
    – JACK
    Mar 7 at 3:06
  • probably fixable depending on how the scoreboard actually works, probably not easily fixable.
    – Jasen
    Mar 7 at 10:54
  • Measure the voltage that the led bulbs are receiving when they are all on. Mar 7 at 11:21

3 Answers 3

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You can fix it, but you may not like the answer, for it's a lot more work than swapping the bulbs.

Electronic switches and LEDs that were not designed to work together often flicker. A solution I use is to add a resistive load, called a ballast, in parallel with each LED. It makes the load on the switch, electrically speaking, "look like" an incandescent lamp, which unlike common LED's, is essentially resistive in nature.

The downsides are the expense and trouble of installing 200 resistors and the heat they generate. You might solder them to the back of the sockets on the scoreboard or more accessible connection points, e.g., at the controller.

The resistor specifications depend upon the voltage of the incandescent lamps. Assuming they are 120V, the resistors would be 2500 Ohms at 10 Watts. Be aware that 200 of them will create 1200 Watts of heat, like a typical space heater, so you'll need to dissipate it with a blower or some such so it doesn't damage anything.

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    They might be able to get away with much less power dissipated while still fixing this problem. If I were facing this issue I would try experimentally first with maybe a couple of 25k or even 50k resistors on a few bulbs. It's pretty common to only need a fraction of the original incandescent load as a resistive load in order to prevent flicker. Also since this scoreboard is almost certainly matrixed, adding the resistance at the matrix outputs could do the trick with a fraction of the total number of resistors.
    – KMJ
    Mar 6 at 16:10
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    @KMJ - I don't disagree. From afar, and with no indication of the OP's electronic skills or circuit details, I aimed for a simple answer that I was fairly sure would work. If it were in my shop, I would certainly explore more elegant options including yours.
    – MadMonty
    Mar 6 at 17:28
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Question isn't clear about when the flickering occurs.

Flickering when "OFF"

If the bulbs flicker when they are supposed to "OFF", that typically means the system is sending a small amount of power through the lights all the time. That works fine with incandescent bulbs (they would glow at an imperceptible level) but LEDs require so little power that they either glow visibly or flicker.

With a simple fixture (1 or more bulbs that are all ON or OFF at the same time) there are some relatively simple fixes. But I have a feeling they won't work in a scoreboard where each bulb is controlled individually.

Flickering when "ON"

This is a common situation when non-dimmable LED bulbs are used with a dimmer or with an incompatible type of dimmer. The solution generally is to switch to dimmable bulbs or to a different brand/type of either dimmable bulbs or dimmer. If the dimmer predates the existence of affordable LED lighting (as is likely the case with this scoreboard) then replacing the dimmer is very likely the solution.

The problem is that a scoreboard is not a typical lighting fixture. It may be constantly sending an "ON-ish" or "OFF-ish" signal to every single bulb at a high frequency, which can easily explain flickering. I can't say exactly which frequency (will vary depending on type of bulb) but sending a moderate frequency (perhaps 10 Hz) power to an incandescent bulb may appear as "ON" but appear as a noticeable flicker with LEDs. If that's the situation then dimmable bulbs may not solve the problem.

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  • How does this help solve the problem?
    – MadMonty
    Mar 15 at 2:07
  • It doesn't solve the problem. It separates the problem into one of a few possible causes, which might help lead to a solution once we have more information from OP. Mar 15 at 2:19
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If the problem is the bulb charge cycles synching up and starving themselves of charging current, rewiring them onto more busses (eg rather than using a single common neutral-side bus for all the bulbs) may improve matters. I have a 16-bulb chandelier with dimmable LEDs, and when dimmed down past a certain point the bulbs will flicker randomly as they fight to draw current to recharge in competition with the other bulbs. Feeding half the bulbs off a separate lamp cord would probably solve my problem by reducing input resistance and lowering the RC timer value.

Note that an issue also exists if the old bulbs were being multiplexed; sufficient current to get an incandescent to glow at a low level may not be enough to charge up an LED bulb. Dimmable LED bulbs may or may not do better in that case. Circuits that rely on dimming/pulsing incandescent bulbs may not be good drivers for LEDs.


Since folks asked for an explanation: The issue occurs when current available to the bulbs is limited and the bulbs are using switching power supplies.

Example: I have a 16-bulb chandelier which is now running with small dimmable 129V LED bulbs, all wired in parallel at a single point. Each bulb only draws a few watts average so this is far below what the chandelier would normally require.

However, the bulbs draw that power in brief pulses of relatively high current, charging up a capacitor, letting it discharge, through the LED, charging it up again. If full power is available they can all get enough energy, often enough, to stay lit continuously.

If I dim the fixture down, then below a certain point the bulbs start competing with each other for the available power; they can't all get enough current to stay lit continuously. At that point, variation between bulbs causes them to recharge at slightly different rates, and rather than continuing to dim smoothly they will fall out of synch, with each one going dark, drawing power until it can light up again, stopping it's recharge cycle (making that power available to other bulbs), staying lit until its capacitor runs down enough to need recharging, going dark until it can complete that recharge, and repeat. The result is random flashing over the whole chandelier, at rate determined by just how far I've turned down the dimmer. This does not seem to happen with a smaller number if bulbs where the peak inrush current if they all try to recharge at once isn't enough to cause the contention.

If the scoreboard is multiplexing the power across the bulbs rather than having a relay per bulb, that could be an equivalent of my dimmer setup, where the bulbs are getting enough voltage, in theory, but may not be getting it at the time when the switcher needs to grab it

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  • What is the basis for the assumption that LED's are competing (and being starved) for current? How would another buss make a significant difference in current flow, given the presumed near-zero resistance of the existing bus? For a 3 Watt 120V LED lamp, I = P/V = 0.025 A, and for 4' of #20 copper wire, the resistance R=0.018 Ohms, the voltage drop V=IR = 0.025x0.018 = 0.00045 V., delivering 119.99955 V instead of the 120 V supply. Even if you added an infinite number of busses in parallel, the best you could do is raise the voltage from that to 120 V, a trivial difference.
    – MadMonty
    Mar 15 at 2:01
  • Not assuming, proposing, based on known behavior of larger numbers of 120VAC LED bulbs wired in parallel. Near-zero is not zero, you're dealing with the effect of switching power supplies competing for current. and the effect can be demonstrated. Reducing the competition reduces the risk of tipping over into flickering mode. I did point out an alternative, which is that if the bulbs are multiplexed that's equivalent to putting them in a dimmer and if they aren't getting enough average current for the switchers to keep their capacitor charged they will fall into the same flickering mode.
    – keshlam
    Mar 15 at 2:45
  • Proving any theory requires experimentation on that scoreboard, eg unscrewing most bulbs to see if flickering stops and, if it does, determine whether which bulbs are screwed in reliably makes a difference (and then consulting the scoreboard's schematics to understand what the differences are).
    – keshlam
    Mar 15 at 2:48
  • I am unfamiliar with the "known behavior of larger numbers of 120 VAC LED bulbs wired in parallel", perhaps you could elaborate. (All such bulbs in my house are in parallel, as are all the bulbs on any phase in any office building - literally thousands in many. None flicker unless they are defective.) As for "non-zero isn't zero", my point is that it's not enough to make a difference. Put a scope on any power line and you'll see much larger variations of all durations with no flickering LED's.
    – MadMonty
    Mar 20 at 2:29

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