Metal-Case LED Light Safety

http://www.algaescrubber.net/240-120-led-light.jpg.....http://www.algaescrubber.net/open-frame-led-med.jpg


Metal-Case LED Light Safety

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This information is linked by LEDsafety.org

With the increased usage of natural algal filtration, comes the increased usage of illumination to make the photosynthetic filtering process occur. However, certain types of metal-case lights have come onto the market, and they need to be addressed because they are potentially unsafe when used on ATS algae turf scrubbers. We do not use these lights, but unfortunately other people do and sell them to unknowing consumers; the corrosion of the metal case lets water reach the dangerous 240/120 volts inside, and a UL-rated power cord does nothing to help, nor does a warranty. If you do not have these lights, then you can decide whether to get them or not. If you already have them, then you can learn how to protect yourself, although it safest to change the lights entirely yourself, or request the manufacturer to change them.

Over time, the problem of the metal case and internal corrosion gets worse, not better. At some point the metal case will reach a critical point due to the corrosive operating environment of sump-mounted waterfall algae scrubbers, which is a much harsher environment than the outdoor gardens (or indoor farms) the lights were made for. Whether this is 6 months or 2 years depends on the light, the scrubber housing, the sump environment, and the usage. The simple solution is to just not use or buy metal-case 240/120 volt lights at all. If you already have these lights, and you are not technically comfortable with electricity, the only safe solution is to have them replaced before corrosion breaks through the seal. Do not believe anyone who tells you their aluminum case lights will not corrode; all aluminum corrodes, especially near saltwater. The only thing worse than "sealed" metal case lights are open-frame metal case lights, which are for indoor use only and have absolutely no protection at all.

Even if you have 1, 2 or 6 of these lights, and they've had no problems for years, that does not mean that other people should not be informed. Imagine if your car had a defect that only rarely occurred, and you were the one that got injured. Would you want the car company saying "There is no defect. We have a customer that has two of these cars and he's had them for three years; if there were a defect then he'd know about it." Of course not. You would want the pertinent information. And as a maker of LED lights, and being an Electrical Engineer, I feel I am qualified to provide this information. If you have additional information, you are invited to post it below, especially if you are a verifiable state-licensed electrician.

Several "commercial" scrubber builders who use these lights were asked to provide input/articles to be included here, but nothing was received from any of them. Also I offered to provide free electrical design advice to improve the safety of their scrubbers, but all of them declined, saying their lights were not dangerous, even though they had no electrical training, experience, or certifications to back this up. And they still use the hazardous lights as of March 2020, continuing to let customers believe the units are safe.

The following is one person's professional opinion on the safety of these metal case, high voltage, algae scrubber lights. You should consult your own professional advice and opinion from an independent electrical engineer, electronics engineer, state-certified electrician, or safety technician before using these lights; if you are making, advertising or distributing these lights then you should also consult with a product liability attorney specializing in electrical injury. Again, we refuse to use or promote these lights.

To subscribe to the updates of this safety information, click here (must be logged in), and select "Notification Type" to be "Instant Notification By Email"...

http://algaescrubber.net/forums/subs...ription&t=3676

The "sealed" metal frame lights are typically used when people build or buy the waterfall scrubber design we invented in the year 2008:

Attachment 7538

The light is a metal-case LED lighting fixture that is bolted on, and is typically made in China and sold online, but it could be made anywhere. It is designed for gardens and patios, with some rain, or for indoor growing areas that get no rain at all:

Attachment 7539 Attachment 7540

We at Santa Monica Filtration were the first to test and use these types lights on waterfall scrubbers in the year 2010, as a way of getting away from fluorescent bulbs. Here is a side-by-side test of LED vs CFL in 2011:

https://www.youtube.com/watch?v=LKcib4YaoTc

The LED lights at first were expensive and cost $150 for one set shipped from China. But the “plant grow” color worked well, and the heat was less. The lifespan was also longer, and it was not fragile to ship to customers. So we started using them on our first waterfall ATS algae scrubbers, which we invented in the year 2008; here is the acrylic box with a bottom shelf for the lights to set on, and a top shelf above the lights for protection:

Attachment 7541

Currently, all waterfall scrubbers for sale by others use this same open source free-to-copy waterfall scrubber design because it kind of works, and because the design was given away for free by us. It has problems, but again, it’s free to copy. And almost all pre-made scrubber builders also now use those metal-case LED bolt-on lights, mainly because they now cost only $5 including shipping from China. This makes the cost of those pre-made scrubbers artificially low, because they don’t have to make the lights safe (or even test the lights for safety), and this transfers the electrical risk to you, the customer. This typical Ebay listing of 20 lights for $99 even says "U.S. stock" to make it less apparent that they are from China:

Attachment 7542

Having invented the waterfall scrubber design in 2008 (water flowing down a screen), we are fairly familiar with how the scrubber works. And how the lights work too. Many people DIY their own scrubbers, and for these people the metal-case LED lights are fine to use as long as safety is observed. This is because DIY people tend to have experience with electricity, water, etc, and they are trusting their own skills to make things safe for themselves. If something goes wrong, only they get hurt. But commercial makers of scrubbers are expected to provide a safe product, because it will be purchased by consumers who are not expected to have experience in electricity. We don’t use those lights anymore. Here’s why, with a focus on safety:

The biggest problem with those lights is the fact that a line voltage of 240/120 volts comes directly into the metal-case light which is a non hermetically sealed compartment; and the light is placed within inches of splashing saltwater and salt-creep that comes out from the top of the scrubber. The scrubber is then placed on top of an open saltwater sump, where there is more splashing and more salt creep. The sump is almost always under a tank, with a simple front cabinet door that lets light out; larger tanks with sumps like these are usually located in a common area of a house such as a living room. Where children play. And it’s commonly known, and almost predictable, that the floor area in front of the sump gets wet, even when the cabinet door stays closed. It does not take much to imagine one’s child opening the cabinet door to see the “pretty pink” light, and then trying to touch it, while standing on a wet floor at the exact moment that that salt creep has shorted the internal 240/120 volts of the light to its metal case. So, the idea of writing this information is to prevent this from happening.

If any scrubber maker can say that this won't happen, I'll listen. As of March 2020, I've heard nothing. And no verifiable state-licensed electrician has spoken up either.

As an electrical engineer (BSEE), people like me are sometimes asked to be expert witnesses in court cases about electrical safety liability. In the USA, electrical safety is tested, and accepted most readily in industry, by Underwriter’s Laboratory (UL). Unfortunately this testing is expensive, and if a Chinese LED light maker pays for the UL certification, the cost of their lights will be much higher (and the certified product will have a “eXXXXXX” number on it). But UL certification shows that a third party has inspected the power supply to be safe, instead of just the maker of the product saying it’s safe. Also unfortunately, none of the Chinese LED lights described above are UL certified, as far as I know. This problem becomes bigger because the metal case of the light (metal is needed to remove heat) is what “protects” the wires and electronics inside. However this metal case in not hermetically sealed (not truly “waterproof”), and indeed because of the $5 cost it is often rushed through assembly where even the rubber seals are incorrectly inserted, or forgotten altogether. Here is an example "waterproof" light from ebay, fresh out of the box; you can see the "waterproof" seal on the 240/120 volt wire is completely not sealed:

Attachment 7554 Attachment 7555

There have been cases on aquarium forums, and on youtube, where the metal compartment screws have not been tight, or were missing. Ground wires were loose, or just cut off. Internal drivers loose and rattling around. Heat sink compound too thin or missing, causing overheating and melting of wire insulation, and even causing steam from water that was splashed on it. Because of this, it’s my personal opinion that using these metal bolt-on LED lights is potentially unsafe in the saltwater environment of scrubbers which are setting on sumps. Googling “chinese led light danger” finds too many results to read, but here are typical ones:

https://www.youtube.com/watch?v=vbt2ojkXPuo

https://www.youtube.com/watch?v=1Pubk8Ets2I

For people not familiar with salt creep (maybe you only have freshwater), it gets into everything. Any crack, surface, or other area inside a sump will eventually get at least a light coating of salt creep, even if the direction of the surface goes upwards. Areas closer to the sump top will get a coating that you can wipe with your fingers, just like dirt on the ground. Areas on the top rim of the sump where scrubbers are placed will get coatings thick enough to require scraping tools. And salt creep is always wet, so yes, it’s very conductive of electricity. It’s the single biggest cause of shorted-out power sockets in sump areas. Any 240/120 volt electrical device in a sump area needs to be hermetically sealed, or else it will eventually get salt creep into it. It might take months, or years, but it will happen. Here are examples:

Attachment 7586

https://www.youtube.com/watch?v=3QAwXCDm8R0?t=96

And here is a more thorough description of residue build-up, which is similar to salt creep but occurs in freshwater too:

https://www.researchgate.net/publica...ity_do_not_mix

What does hermetically sealed mean? It means it's air-tight. And if it's air-tight, it's waterproof. It would be difficult to make the metal-case lights air-tight, because you would have to basically weld the case together. The most common way of making electronics air-tight and waterproof is make them a solid component, like we did with our GEM lights. No air space inside at all:

Attachment 7587 Attachment 7588

All other aquarium sump equipment has the 240/120 volt area hermetically sealed: power heads, heaters, etc. The metal-case LED lights that are being used for algae scrubbers by some people seem to be the only equipment not sealed properly.

Related to salt creep, is corrosion creep. Because the metal case of the bolt-on lights is aluminum, it can corrode slowly (even in freshwater) where the seal is located, especially at the top of the light where water splashes onto it. So even a seal that is designed and assembled correctly can be pushed sideways by corrosion creep, and eventually the seal will not be sealed anymore. And if it’s on the top of the light, water can now drain directly down onto the 240/120 volt electronics inside, and you won’t see it because the corrosion is on the inside of the seal area. A stainless steel case would prevent this, but low cost metal-case lights are never stainless. Stainless enclosures are used in underwater 240/120 volt pool lighting, but those lights start at $100 each. Here is a pool accent light with a single 3 watt LED inside, and it is $40; note how much stainless steel is needed to protect it:

Attachment 7607

The best way to slow down corrosion is during disassembly inspection: coat both sides of the metal case (where they touch together) with grease or petroleum jelly, and re-insert the seal, and re-assemble. Ongoing disassembly and inspection every 6 months is advisable. Unfortunately, each month that goes by will allow more salt and corrosion creep to occur, and the seal will only get worse, not better. And, just like the Chinese do, you might actually mess up a seal during re-assembly, which was fine before you took it apart. So be careful.

Interestingly, most commercial scrubber builders use absolutely no metal in their main boxes which hold the algae growth, because of course the metal would corrode. There are many low cost metal boxes that could be used, which would not crack during shipping like acrylic/perspex does, but builders instead take the time to hand-construct boxes out of acrylic/perspex so that corrosion will not be an issue. So why then do they allow metal on the lights (the most important area for safety) if they know it will corrode?

The reason again is simple: Cost. Just $5 to $8 each, including shipping from China. But the Chinese know that if someone is injured because of these lights, nobody will be going to China to sue them. So the Chinese have absolutely no need to make things safer. It’s up to the DIY person to check each light (by taking it apart), and it’s up to each commercial scrubber maker to request UL certification, non-metal construction, low voltage operation, and hermetically sealed enclosures. Like we did with our GEM lights.

It's my opinion that all of the low cost metal-case lights are made in China, even if they have been relabeled to look otherwise. I've spent hundreds of hours trying to find lights (and other parts) in the USA, only to be directed to China every time. The cost of the metal castings for the case alone would be $10 or $20 each, if made in the USA. And the labor to assemble the electronic and other parts would be another $30 at least. So manufacturing in the USA is not an option for these types of lights, and if they say “Made In USA” you should assume this is not true. This was yet another reason for us to abandon these metal lights (and their internal electronics design) and go with our non-metal cast molded low voltage design instead, which we make right here on our desks in Santa Monica, California, USA. But even if the bolt-on metal Chinese lights were made in the USA, and even if they were UL certified, you still have the problem of the electronics enclosure not being hermetically sealed. So if water, or steam, or salt creep gets inside, and you touch the metal case, it’s not going to matter who made it, or who certified it, or what the warranty is. This was the final reason for us separating the power supply away from the light, so that the 240/120 volts would be 2 meters away from the splashing and salt creep:

Attachment 7608

Some people will say, "These lights are safe, because they were made for outdoor use in the rain".

First of all, this is assuming that the lights were put together correctly in the first place. Open up a few and check for yourself to see if the ground is connected properly, or if it was just cut off completely. If it's not connected properly, you can forget any safe usage, anywhere. As a matter of fact, if the ground is not connected properly, usage in the corrosive saltwater environment of a sump is (at least) very dangerous, and in my opinion could be described as deadly, when the operator is an unsuspecting and non-electrically-aware consumer (or worse, their children, standing on a wet floor) who bought the scrubber thinking the manufacturer did all the proper safety designs and certifications.

Second, even if it was put together correctly, usage in an outdoor area or garden usually means the light will be staked into the ground, or will be attached to a metal conduit, both of which provide a ground path if the internal 240/120 volt circuit gets shorted to the metal case. Plus, you don't normally touch, grab, or usually even go near these outdoor lights in a garden. So even if they shorted internally to the metal case, and even if the ground wire were missing, you would not be anywhere near it.

Third, the water falling onto the lights in a garden area is just freshwater. Compare these things to a saltwater sump:

It's bad enough that the ground might not be connected, but regardless, the installation is on the top of sump that is not grounded. It's not a garden bed, and it's not a metal conduit grounded to a house. Instead it's an electrically-floating acrylic box filled with water. It's a really, really bad place to have a possibly non-grounded product, or even a grounded product that is likely to eventually leak.

And the usage requirements of these scrubbers requires weekly, and sometimes daily, touching and grabbing of the lights. With wet hands, and while standing on a wet floor. Ask any licensed electrician if he would like to be doing this.

The 240/120 volt power supply in these lights is inside the metal case which holds the rubber seal in place. All metal corrodes, especially aluminum, and especially in saltwater, and when the metal corrodes enough around the seal, the seal will leak. And the most dripped-on part of the light is the top, and that is directly above the internal power. So, the water drips down directly onto the high voltage inside. Look at how the lights are usually mounted: the seam of the seal at the top is directly over the internal power supply.

They're terrible. I bought some with 660nm leds in and they came supplied with only live and neutral had to fit a new 3 core cable. Amazes me how UK sellers are not prosecuted for selling these.

My understanding is that UK/EU sellers are required to have proof of safety certification of the entire product before selling or distributing it. This requirement does not exist in the U.S., however, when a consumer injury occurs in the U.S., a product liability attorney will usually go after the manufacturer and also the distributor/reseller that sold the product to the injured consumer.

When they come in direct from China that is bypassed because so much stuff goes unchecked at customs. Unfortunately, a lot of the "UK" sellers are based in China, so difficult, if not impossible to enforce upon them. Mention it to genuine UK sellers and they act shocked and "don't realise"!!!

Another dodgy area is 13A plugs in the UK. Some items don't need to be earthed, so a plastic earth pin is acceptable. Class 1 appliances must be earthed and plugs must comply with BS1363. This means the earth pin should be completely metal. Some cheap plugs/ pc leads come with a earth pin with plastic at the top totally illegal!! Finally, I have purchased items with a dummy UK plug which looks identical to a real one, but.... There is no fuse holder inside!!!

Lets be careful out there folks. The World is easier to trade with these days, but safety standards are universal!!!

Another problem with most of the metal 240/120 volt lights, is that in order to save more money, they often make the 240/120 volt cord very short, usually just a few inches:

Attachment 7726

This means that the rest of the 240/120 volt wire needs to be connected at this point, and almost any connection made by anyone is not going to be hermetically sealed. This connection is going to be placed directly over open areas of sump water, and therefore it’s going to get a lot of salt creep and even direct splashing. There is no fix for this; the wire should be replaced entirely.

If you are going to DIY and already have a set of these metal-case lights, you are best advised to not use them and just get a safer light instead. At the very least, use a GFCI protector, available at any hardware store. A safer option would be a low voltage DC version of the same light, with a remote power supply that either comes with it, or that you get and connect yourself (just make sure to get a UL certified supply if it's for the USA). With a really long 2-meter DC cord like we use, the 240/120 volts can at least be placed far away from the sump. However, this does not solve everything for these metal case lights.

Splashes from the sump, and from the top of all-in-one nano tanks, can easily reach the power supply box especially if the box is kept in the sump cabinet or behind the cabinet on the floor. A splash (or even very thick wet carpet) can short the 240/120 volt AC side of the box to the low voltage DC side, effectively electrifying the "safe" side to 240/120 volts.

These low voltage DC lights typically are not grounded on their DC side, so when the 240/120 volts hits the LED diodes inside, the diodes are either going to fail open, or fail closed. If you are having a bad day, they will fail closed. The lights typically use Chip-On-Board (COB) designs which put the diodes within one millimeter of the ground plane, and a 240/120 volt shorted diode will easily arc to the nearest piece of metal which is probably now going to be the metal case. So you once again have a 240/120 electrified case waiting to be touched in your sump area, and you will no doubt be touching and grabbing the light to inspect why it is no longer turning on. Thus even low-voltage metal case lights can be electrocution hazards.

The metal case of these lights is a major problem for safety. Metal obviously conducts electricity, and any 240/120 volt wire that touches the inside of the case is going to electrify the case and cause an electrocution hazard. Especially when you remember that the floor where you are standing is often, and predictably, wet. Unfortunately since the metal case is also the enclosure for the electrical parts, there is no DIY or pre-made solution for this. All you can do is disassemble each light and inspect for visible problems, and test for electrical safety. And if you don’t know how to test, get an electrician to do it for you; the metal case must be grounded to earth.

I have noticed that these lights are now on sale with a 12v supply. I have 2x 230v of these lights with 660nm led in that I have never used because of the safety aspect. I think the 12v supply is a good way to go, but finding a seller that also sells them in other than white! Another suggestion could be to remove the 230v driver from the light casing and extend the 12v side, leaving the driver outside of the aquarium environment.

This is better, yes. But for manufacturers, you can never depend on what the customer will do. They may set the 12v supply next to their sump and easily spill water on it, thus shorting the line to the case/LEDs and once again putting 230v into the case as described above.

Also can't depend on customers using a GFI.

Some scrubbers, both DIY and pre-made, have an open top. We created the first open-top scrubber box, but decided even in 2008 to put a cover over it because of the large amount of spray and salt creep coming out of the top. Here is one of our forum posts in 2008 showing the design:

http://www.reefcentral.com/forums/sh....php?t=1424843

Before this design in 2008, scrubbers were either dumping buckets or horizontal rivers. Those worked but had even more problems than our waterfall, and the buckets/rivers were not 2-sided like our waterfall was (with lights on both sides of the growing surface; very important for filtering). But even with our waterfall, the screen sometimes would fill with growth and would clog the water slot, causing water to spray up and out of the box, onto the lights. Back then we watched for this, and DIY people even expected it. But using metal-case lights on a open-top box could have water spraying directly onto the lights, which as shown above, could leak right into the case through a seal that is no longer sealed.

Attachment 7795

The DIY and the pre-made solution is to close the top of the scrubber box. However this does nothing during cleaning/harvest time, because the pipe and screen need to be lifted up and out of the box, and this causes lots of saltwater to drip down directly onto the lights. Even pieces of algae will fall onto the lights, seeping into the seal:

Attachment 7796

Our solution with our RAIN design was to switch to a dome with our submersible non-metal GEM lights:

Attachment 7797

Another hazard of our previous waterfall design, especially when there is no top “shelf” covering the light, is that in order to lift the screen out of the box (for cleaning) you need to place your other hand onto the box to hold it down; the proximity of the lights (to the top) causes your hand to touch the metal case when doing this. This is the worst case scenario for electrocution because as you learn when repairing televisions, it creates the most direct and shortest path of electricity from one arm to the other, directly through your heart. The DIY solution for this is to make a large top shelf over the lights that will absolutely not allow your hand to touch the lights. The pre-made solution can be similar, but the real solution is to change the power supply to a remote low-voltage, AC/DC isolated, UL certified power supply. Like we did.

A safer solution that all DIY and commercial scrubber makers can use is a remote “switching” power supply with at least 3000 volts isolation from the mains, with a long 2 meter DC cable so the 240/120 volt box can be far away from any splashing, wet carpet, interested children, pets, etc. The power supply needs to be UL certified with the “eXXXXXX” number on its label, so you can cross-check its manufacturer yourself on the UL website. We have had more than one Chinese supplier say they had UL certification, but upon checking, they were actually using the number from another company and thus providing an inferior untested product, even though the price was increased! Lastly, the enclosure for the lights should not be metal, even if they are low voltage. This will protect the customer even if the power supply box is splashed because the 240/120 volts will not have a metal case to conduct to, and injure, the customer.

Speaking of injury, when a personal injury attorney contacts a commercial scrubber maker because of an injury claim, it might go something like: “So, you are saying that your 240/120 volt device, being sold in the U.S., has no UL certification. And it places 240/120 volts within a single hand’s distance from saltwater. And the pink light, known to attract children, is visible from outside the aquarium cabinet, and the floor in front of the cabinet is often, and predictably, wet. And your device has no GFCI or RCD circuit or other means of breaking an electrical short. And, these waterfall scrubbers are known to spray water upwards and outwards, onto surrounding surfaces, such as the surface that my client’s child touched?” This will be indefensible.

240/120 volts simply has no business being inside of a non-hermetically sealed metal enclosure that is subjected to hand placement, salt creep, and direct splashing by saltwater. The commercial pre-made scrubbers using these lights are the only aquarium equipment I know of that does this, and they need to be made more safely. So I challenge all pre-made commercial scrubber makers to replace their metal case lights with safer options. Yes these options will cost more, and you will lose a lot of your profit. But I bet you can do it. Like we did.

Further, all customers that already purchased metal-case lights should be offered to have the lights replaced with safer alternatives. Each month that goes by allows corrosion and salt creep to penetrate into the seals further, and so the sooner these hazardous lights can be replaced, the better. Eventually, all the seals will leak.

Commercial scrubber makers have the final say in obtaining professional electrical safety design advice; specifying safe components; assembling the components properly, marketing them accurately, and standing behind them with personal injury liability insurance coverage. Here is a checklist that you can send to anyone you want to buy a pre-made scrubber from (you can also use it for buying just the lights, although some of the questions will not apply). The fewer answers you get from these questions, the more concerned you should be:


- Is their overall scrubber design certified by an electrical engineer, electronics engineer, electrician, or safety technician who can testify as an expert witness in a personal injury court if required to?

- Do they have personal injury liability insurance for their customers?

- Are they a licensed business in their city?

- Do they have a DBA (Doing Business As) license in their county?

- Do they have a reseller's permit in their state?

- Is the enclosure for the 240/120 volts certified (in the USA) by Underwriters Laboratory, with an "eXXXXXX" certificate number printed on it?

- For metal enclosures, has every enclosure had it's ground path tested to the ground pin of the power plug before shipping?

- If the lights are placed into saltwater, will they continue to function indefinitey? This is the amount of time that salt spray will be attacking the seals, indefinitely.

- If a remote power supply, and if the power supply box gets wet, is the metal case insulated from the 240/120 volts?

- If the 240/120 volt cord goes into the enclosure for the lights, does it have a non spliced length all the way to the plug?


Thank you for reading, and for wanting improved safety in your home!

Note: The above is one person's professional opinion on the safety of algae scrubber lights. You should consult your own professional advice and opinion from an independent electrical engineer, electronics engineer, electrician, or safety technician.

Now I would like to point out an even more dangerous light: the open-metal-frame indoor plant grow light. The "waterproof" lights I covered above are bad enough, but now people are starting to actually use indoor non-waterproof lights that not only have an open-air frame for water and algae to get into, but also have open 240/120 volt connections in the direct path of water:

Attachment 7812

Not only are these lights not going to last in the salt air humid environment of a sump, but out-of-the-box they create an extreme electrical hazard:

- The open frame allows water to drip down directly onto the high voltage components inside.
- Salt spray is going to get pulled through the unit, via the fans, which will corrode and/or short internal components.
- The open high voltage power cord connections are in the direct path of splashing, dripping, and even simple accidental dropping into the sump.
- Internal condensation, which already happens with the "sealed" type of lights when moisture eventually gets inside, is going to happen on the first day with these open-frame lights.
- Placing these lights into enclosed scrubber boxes reduces the circulation of cooling air, which further stresses the internal components.
- Using this type of light is the same as putting a toaster near a bathtub; all circuitry is directly exposed to water. Even if it's a UL rated, it's irrelevant.

Since these lights are clearly labeled (or should be labeled) as indoor-only, any usage of them in a worse-than-outdoor situation (such as a wet saltwater sump) puts a manufacturer or distributor in a very bad situation of negligence and possibly willful negligence. Please do not use these lights in a waterfall algae scrubber.

Here is an example of how truly waterproof submersible lights can go underwater safely.

Attachment 8252

Here is what can happen if a drop of water gets on the AC connection (or inside) of an open-frame LED light, or if the AC cable of a 240/120V light gets corroded:

https://www.instagram.com/p/CveFoIUsXmP

Attachment 8567