Using 100W/120V Light Bulbs with Arduino

I want to use an Arduino Mega to turn 8 100W Light Bulbs on and off. I am not sure what to use to supply power and control the light bulbs.

I wanted to use these light bulbs: Ace 100 watt PAR38 Floodlight Incandescent Bulb E26 (Medium) Green 1 pack - Ace Hardware

Any advice would be appreciated to accomplish this project.

Thank You.

Might be nice to know what exact LEDs you are using. Just on/off or control brightness (fade)?

I want to use an Arduino Mega to turn 8 100W Light Bulbs on and off. I am not sure what to use to supply power and control the LEDs.

Light bulbs or LEDs ?
Which is it ?

@TWA2020 - editing a post that has already been commented on as you did is impolite at best as it can make nonsense of the comments. Please do not do it again

From the linked page.

Ace 100 watts PAR38 Floodlight Incandescent Bulb E26

Incandescent bulbs. 110VAC? You can use a mechanical relay or a Solid State Relay (SSR). A mechanical relay will need a driver to be controlled by an Arduino or buy relay modules with the driver included. Make sure the relays have the right current and voltage ratings.

Check the total curreent.
In the U.S. we have an 80% rule.
You can use up to 80% of the rating of a circuit breaker.
15 smp and 20 amp breakers are common in the U.S. with 20 amp the minimum for receptcles.

Do you have an example mechanical relay and Solid State Relay I could use with an Arduino?

Google "arduino relay" or "arduino solid state relay" for examples.

There are commercially made units available which allow uC control to be done safely.

iot2spec.pdf (188 KB)

100W at 120V = 0.96 Amps, these SSRs are rated 2 Amps.
SSR Board
Or to switch all 8 at once:
Single SSR

When I look online for a part to buy what specifications do I look for?
Such as what voltage and amperage are necessary for these light bulbs?

120V/20A

JCA34F:
Or to switch all 8 at once:
Single SSR

The Amazon page says this is a 5V Solid State Relay Board. Will it power the 120V light bulbs?

Your household wiring powers the light bulb.

The Amazon SSR (solid state relay) can be switched on/off by a 5V Arduino output, connected to the relay control input, and will in turn switch 120 VAC circuits on/off.

Beware that there are very dangerous fakes of that Fotek SSR on the market.

Finally, when starting up, a 100 Watt incandescent bulb draws about 10 Amperes, or 10 times the normal current, so that relay is rated to switch only two 100 Watt bulbs in parallel. If switched on at the same time, eight 100W bulbs in parallel will probably pop your circuit breaker, so you should plan on switching the bulbs on sequentially.

What is the difference between a FOTEK SSR-25DA and one of these?

So, it does not matter what the output of a relay is as long as the input is 5V, which is within the range of what will work for an Arduino. A 5V relay can handle any input voltage, even if it is straight from the wall power outlet at around 120V and 20 amps. Is that all correct?

Also, what difference does it make if I buy a SSR rated at 25 amps (FOTEK SSR-25DA) versus one at 40 amps (FOTEK SSR-40DA)? would the 40 amp SSR provide too much power and not work for light bulbs?

would the 40 amp SSR provide too much power

Your household wiring provides the power. The SSR is just a switch.

What is the difference between a FOTEK SSR-25DA and one of these?

There are hardly any similarities, except that both use SSR switches.

The latter is totally inadequate for your project.

The Amazon page says this is a 5V Solid State Relay Board. Will it power the 120V light bulbs?

Yes. It's controlled by 3-32VDC and it can switch 24-380VAC at up to 25 Amps.

The current rating on a relay is the maximum. It's OK to use a high-current relay in a low current circuit. Except there is some leakage current with solid state relays so a low-power light bulb might glow dimly when the relay is "off". (Your 100W bulbs will be fine.)

Wattage is calculated as Volts x Amps, so at 120VAC 100W is about 1 Amp. But as jremington says , the initial turn-on current for an incandescent bulb is a higher so you should allow some safety margin, and you should allow some safety margin anyway. I don't think you'll pop your breaker. Circuit breakers have a little delay. I've made a sound activated lighting effect with 4-channels and it doesn't blow my 15A breaker with 2 100W floods on each channel.

(If you ever use a motor with a relay, motors have even-higher start-up current.)


There are solid state relays (such as the one suggested) that can be directly driven from the Arduino's 5V, low-current outputs.

These "industrial type" of solid state relays with screw terminals are super-easy to wire-up and mount. (The relay board also has screw terminals.)

The output-side of a solid state relay is a little trickier than a regular relay because AC & DC relays are not interchangeable and sometimes there is a minimum switching voltage.


Regular electro-mechanical relays have a coil (an electro-magnetic to pull the contacts together) and there relays with 5V coils, but 12 or higher is more common. The Arduino can't supply enough current for a relay coil, so you need a driver circuit, but you can buy relay boards with a built-in driver and relay.


Then is the 25/40 amps a measure of how much input power (amperage) can come into the relay switch to control it, which is irrelevant with the low amperage of the Arduino?

The 25/40 amps is an indication of how much current the relay can switch. It has nothing to do with the voltage used to actually switch it on which is provided by the Arduino

The whole point of a relay is to allow a high current and/or voltage load to be controlled by a lower voltage/current signal as provided by the Arduino

@TWA2020

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