# How fast can a 120VAC LED bulb be switched on and off? (Without serious damage)

Since LED's run on DC and the 120VAC replacement bulbs receive AC power there must be some electronics inside to step down the power.

Can these electronics handle the bulb switching on and off rapidly? By rapid I mean 1/8 second on then 1/8 second off repeatedly.

I am using an Arduino to control ~20 independent 120VAC 60w equivalent LED bulbs. I am asking the question here since it is more electronics than Arduino programing but wanted to give context to the question.

• LEDs by themselves can be switched on/off very rapidly. But you want to switch on/off the mains voltage I guess. The power supply circuits in 120 VAC LED lightbulbs are not designed for rapid on/off switching. I doubt if you can find any manufacturer willing to state that this would be OK for their lamps. Some might be OK with it, most will probably not be OK and break after a short time. Sep 5 '16 at 14:45
• You need to explain what it is that you are trying to accomplish. Without that context, this devolves into a question about how to use a product, which is off-topic here. Sep 5 '16 at 14:51
• I want to blink the 120VAC bulb off and on rapidly useing an Arduino and a Solid State Relay. I have the system working with a mechanical relay at about 2 operations a second. I want to replace the slow mechanical relays with the SSR and speed up the on/off operations per second. If this is not enough context I can explain more and post pictures. The reason I am asking about the bulbs is because originally the mechanical relay was the limiting factor on the speed. Now with the SSR the bulb might be and I wanted to try to determine a relatively tolerable on off switch rate. Sep 5 '16 at 14:54
• @FakeMoustache Yes, I want to switch off the mains voltage. I do not mind if the lights break sooner or have a shorter lifespan. Thank you for your answer. I figured that they were not designed for that but wondered if they would tolerate the rapid switching for a limited time. Sep 5 '16 at 14:57

As pjc50 says, ensuring complete half cycles would be wise.

Some LD drivers use hill & valley circuits which store energy in series capacitor chains when voltage is high and use the capaciors in paralle as Vin drops. This is arranged using diodes and capacitor - ie no active devices in the usual sense. Interupting such charge-discharge cycles at random places mid cycle could lead at a minmmum to unpredicatbel lighting behaviour and MAY lead to componen failure. Maybe not.

Zero crossing should be easily arranged - at which stage you can probably safely use individual half cycles or 100 / 120 Hz at 50/60 Hz mains.

So your 1/8th second periods becomes 120/8 or about 15 complete half cycles. I'd expect that to (probably) work acceptably with zero crossing switching.

• Thank you. Since there can be no specific answer except for test the actual components, I consider your answer with @pjc50 's suggestion to just try and see, to be a complete answer. I will try it out and just not switch them to fast. Sep 5 '16 at 15:50
• @Artentify - My key points were (1) Switch at zero crossings using a zero crossing driver. (2) As liitle as a single half cycle off or on may be OK. || You are welcome to change the "accept" over to PJC50's answer if you wish. Sep 5 '16 at 16:25

It depends.

There are various designs possible for these bulbs, some of which handle it better than others. It also complicates matters if they're supposed to be "dimmable", which means they try to detect the short on/off cycles applied by a triac dimmer and turn that into a smooth brightness level. I had a set of those that, if dimmed below about 25%, turned into strobe lights.

At least try to use a zero-crossing triac system so you don't turn them on or off while current is flowing. That avoids being detected as dimming.

• Thank you. I have the non-dimmable kind. I have the bulbs hooked up to optoisolated Solid State Relays (SSR). They are inexpensive "EcoSmart" brand bulbs from a big box store. If they have a simple switching power supply would that handle the quick pulses of 120VAC? Which type of circuit in the bulb would be the best the have? I can open one up to see what kind it has. Sep 5 '16 at 14:51
• I think the only sure way is to try it and see if it works with those particular bulbs at that particular speed. Preferably while comparing their temperature profile to a bulb that's just on all the time. And some sort of measuring system of the actual on/off times - phototransistor or fast camera. Sep 5 '16 at 15:18