Wattage ratings on lamp fixtures - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: May 06, 2025, 02:17:02 am
content: I understand that lamp holders/shades/fixtures will typically specify a maximum wattage for a globe, due to damage that could be caused by heat from higher-wattage globes.I picked up a lamp not long ago and the sticker inside the fixture has two values. It specifies 25 watt max. for regular incandescent globes, and 6 watt max for LED.What's the purpose of the second figure? Surely as long as you remain 25 watts or under, regardless of the lamp technology, it should be fine, right?

author: MK14
author_rank: Super Contributor
timestamp: May 06, 2025, 02:45:36 am
content: My theory (I'm open to being wrong), which seems to be mirrored, by other people, by searching the internet.Is that, for the incandescent bulbs. The bulb itself, had no problem with heat, so the only concern was its heat, NOT damaging or posing a fire-risk etc, to the lamp-fitting.But, with (usually) low wattage LEDs, it is the other way round. I.e. The lamp fitting can probably easily cope with the considerably lower wattage. But the LED lamp, doesn't like heat and can have its life considerably shortened, if it can't get adequate air-flow to keep itself cool.Hence the LED wattage limit, is probably an indication of how well an LED lamp, will be cooled (or not), by the lamp fitting.I've literally, had LED bulbs which 'burn out', too frequently. Due to 'old' style (incandescent) lamp fittings, not giving them enough air-flow. Enclosed lamp fittings, seem to be the worst (supposedly long life LED bulbs, even expensive ones, were burning out after only around 3 months, approx).

author: u666sa
author_rank: Frequent Contributor
timestamp: May 06, 2025, 02:48:46 am
content: They had to write something. That's what it is. You should be fine with 30 watts LED.

author: Halcyon
author_rank: Unknown
timestamp: May 06, 2025, 02:50:53 am
content: Quote from: MK14 on May 06, 2025, 02:45:36 amThat seems logical.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 06, 2025, 05:06:30 am
content: This may also be a stupid lawyer entry. A 30 Watt (Power input, not "incandescent light equivelant") LED could easily cause eye damage and possibly sunburn. So a liability prevention limit was posted.

author: Halcyon
author_rank: Unknown
timestamp: May 06, 2025, 05:16:40 am
content: I should add that the lamp base is an E14 Edison screw. Surely, they aren't available in high wattages? Although I suppose you can get all kinds of non-compliant junk from China these days.

author: Whales
author_rank: Super Contributor
timestamp: May 06, 2025, 05:54:12 am
content: Seems like garbage to me. I suspect it might be as simple as someone realising that 6W LED is "equivalent" to 25W incan and therefore thinking it would be useful to put that on the label, without knowing the reasons behind this limit and that this "equivalence" is not valid here.

author: IanB
author_rank: Super Contributor
timestamp: May 06, 2025, 06:01:54 am
content: Quote from: CatalinaWOW on May 06, 2025, 05:06:30 amQuote from: Halcyon on May 06, 2025, 05:16:40 amSeems unlikely that such high power bulbs would be available. When I was looking for an LED replacement for a 150 W incandescent, I could not find such a thing. I think the thermal management problems for such high light outputs make bright LED bulbs hard to construct.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 06, 2025, 10:09:37 am
content: Quote from: Whales on May 06, 2025, 05:54:12 amI think this has nailed it.

author: MK14
author_rank: Super Contributor
timestamp: May 06, 2025, 02:25:02 pm
content: Quote from: Halcyon on May 06, 2025, 02:17:02 amOther peoples replies, made me even more curious, so I've been reading up on it.(I accept room for errors and misunderstandings on my part).It seems the LED bulbs, are nowhere near as simple, or straight-forward, as they would appear.The (reduced) ratings, are needed, to meet the regulations and/or safety requirements. Because of a number of not so obvious things about them.I will detail just two of those things.Firstly, although the wattage, appears to be lower than incandescent. For some of the LED bulbs, most of the waste heat, can be created, mainly in the base of the LED bulb. So, rather than a larger amount of heat, being spread over most of the fitting, it is concentrating the heat (in some cases), in the base. Which the fitting can struggle to safely and/or without damage, handle. As it was originally designed for incandescent bulbs. (unless very modern).Secondly, the wattage is not as low as it would seem. Because the (typical) design of LED bulbs, can have a very significant capacitance. The inrush current, can be massive, especially if the mains happens to be at near peak voltage, when the light is switched on.That can exceed the ratings of the fitting. Especially as regards its switch contacts and/or other contacts.So, it seems the reduced wattage ratings, in some cases, really are needed, to preserve the life expectancy, quality and safety of the light fitting.

author: AVGresponding
author_rank: Super Contributor
timestamp: May 06, 2025, 04:32:14 pm
content: Yep, at least in part. LEDsshouldbe way more efficient than theyactuallyare in service, which seemsmostlyto be down to over-driving them horrendously. Whether this is an intentional lifespan limiting strategy is another discussion.Though the inrush current can be quite high, it's relatively trivial on a per-lamp basis, due to being of very short duration, and only comes into play when you run arrays in office buildings, for example, when you might have to pick either a C or D curve MCB, or in extremis, use contactors.Intheoryyou should run into thecurrentlimit for a fitting long before you reach thepowerlimit, with LEDs. In practice, the LED lamps tend to cook themselves (rather than the fitting), if you watch Big Clive you'll see the two most common failure modes are dried out and dead primary side bulk cap, and burned LED segment. If they live long enough, the phosphor can degrade pretty badly too.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 06, 2025, 05:26:22 pm
content: Quote from: IanB on May 06, 2025, 06:01:54 amYou know this. I know this. Most people in this forum know this. But based on the legal warnings I see, either lawyers are totally ignorant about a great many things, or they assume people will cobble together any dumb thing possible. The latter is actually true, but it is just as silly because such people usually don't read warnings and if they do, don't heed them.

author: edavid
author_rank: Super Contributor
timestamp: May 06, 2025, 06:05:58 pm
content: Quote from: IanB on May 06, 2025, 06:01:54 amThis has changed. You can readily find 150W, 200W, 300W equivalents.For example, Ecosmart 300W equivalent, 30W, 4000 lumen - $6 at Walmart.https://www.walmart.com/ip/Great-Value-High-Output-A23-LED-Light-Bulb-30-Watt-300W-Equivalent-Soft-White-E26-Medium-Base/129040820

author: Whales
author_rank: Super Contributor
timestamp: May 06, 2025, 08:31:40 pm
content: QuoteDunno. I suspect it would be only a small difference.QuoteThis doesn't matter for light fittings.The inrush current will last far less than a second. The metal of the lamp fitting has a lot of thermal mass compared to things we normally worry about being impacted by peak inrush (eg tiny transistor dies & capacitor surface areas). This will heat it a tiny bit more than usual when it is at its coldest time anyway, normal operation for 5 minutes will bring it to a higher temperature.

author: TimFox
author_rank: Super Contributor
timestamp: May 06, 2025, 08:32:47 pm
content: As a matter of personal policy, I never advise anyone to exceed a manufacturer's power rating, especially for line-operated devices.

author: Whales
author_rank: Super Contributor
timestamp: May 06, 2025, 08:34:17 pm
content: It's ok, just use a 25W florescent light, the manufacturer hasn't specced that

author: TimFox
author_rank: Super Contributor
timestamp: May 06, 2025, 08:38:52 pm
content: Quote from: Whales on May 06, 2025, 08:34:17 pmIf the manufacturer forgot to specify against it, could one install a powerful vapor light?

author: thm_w
author_rank: Super Contributor
timestamp: May 06, 2025, 09:43:13 pm
content: Quote from: Halcyon on May 06, 2025, 05:16:40 amI can't seem to find any specs for E14 as to a hard limit.But you can find E14 sockets with manufacturer ratings of 100-200W, and E26 sockets rated up to 250 or 660W.Here is a ceramic E14 rated 500W even:https://www.ledlight.com/e14-socket-with-screw-terminal.aspxSo to say its "non-compliant", you'd have to first give some proof that a universal spec exists.

author: Sensorcat
author_rank: Regular Contributor
timestamp: May 07, 2025, 01:26:53 am
content: My explanation for the specification is different. It has the advantage to not require the speculation that everyone involved was an idiot or a lawyer.The power used in the lamp, whether it is an LED or an incandescent lamp, is split into three parts:Resistive loss, directly converted to heat, leaves the lamp by conductionVisible light, emitted as radiationIR light, emitted as radiationThe difference between LED and light bulb is the temperature. While the LED will hardly exceed 150°C, by a process that does notrequireheat, the light bulb emits light onlybecauseit is hot, usually more than 2000°C. Since the radiation, according tohttps://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_lawis proportional to T⁴ with the absolute temperature T, the light bulb emits a large fraction of the lost power as IR radiation, while the LED can radiate almost nothing as IR. Since the manufacturer must assume a worst-case scenario for specification, this would mean a mediocre LED efficiency (still far better than the light bulb).Example (not exact values):6W limit for LED, 33% worst case efficiency, 0% = 0W IR, 4W conducted into the fixture25W limit for light bulb, 5% efficiency, 80% = 20W IR, 3.75W conducted into the fixtureIn the wikipedia article, in the section 'Examples', there is a nice log-log plot to illustrate the emission vs. temperature, which allows to skip the math. While 1 m² at 100°C would emit about 1kW, it emits about 1MW at 1700°C. More convenient for our problem is an emitter surface of 0.1cm²: 100°C => 0.01W ('almost nothing'), 1700°C => 10W ('a large fraction').

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 07, 2025, 02:44:31 am
content: Quote from: Sensorcat on May 07, 2025, 01:26:53 amWhile these numbers happily match the posted limits the analysis is oversimplified. That doesn't mean it wasn't what was used, just means it gives answers which don't really pass muster. The hidden assumption is that base temperature is the limit and that 4 W conducted into base will cause unacceptable heating. Seems very unlikely to me. Particularly for a base rated for incandescent use, where a sizable fraction of the IR does not leave the area but is reabsorbed by either the bulb or the base. Where some sizeable fraction is then conducted to the base or re emitted at still longer wavelengths.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 07, 2025, 10:14:11 am
content: It seems the only answer is to actually measure the temperature of the light fitting with various incandescent and LED bulbs. Then we'll have hard data.

author: Psi
author_rank: Super Contributor
timestamp: May 07, 2025, 10:19:07 am
content: My advice is to forget lamp fixtures and find a way to use quality LED strip lighting instead. It doesn't have thermal issues, or you can set the brightness if it does get a bit hot, so it lasts forever and you can replace the PSU module if that dies without needing to replace the lighting.

author: MK14
author_rank: Super Contributor
timestamp: May 07, 2025, 11:40:27 am
content: Disclaimer: I don't design light fixtures, or work on light fixture regulations. So, please don't take it as advise.Hypothetical thought experiment, if just for this post, I was to outline how the regulations/ratings might be determined, from a sketch on the back-of-an-envelope, quality level. To make it more obvious/easier to explain/understand.There was mains voltage wiring near the base, with some material thermally insulating it from the base itself.If the base gets too hot, it could over-heat those wires, making them unsafe (electric-shock hazard, fire-risk, etc).So, we (hypothetically), would need to consider the worst case scenario. So it (the base) might run fairly cool, normally, MOST of the time. But it is the reasonable, worst-case scenario, the regulations would need to worry about.So, with a 25 watt incandescent bulb, the worst case base temperature can be calculated/estimated.With LEDs, they would need to consider the worst LED (manufactured) type that the users might install into it (with most/all of the electronics crammed in the base, with the least efficient LED bulb out there, on the hottest day of the year, etc).I'm not clear, if they would also consider reasonable fault situations, such as when the LED bulb, finally packs in (lights up for the last time). When one or more of the components, especially due to the heat stress, has given up and gone open or short-circuit.Because (certainly for my experience of compact florescent bulbs), the base can actually start smoking (Edit: I don't think mine actually were smoking, when I saw them. But as well as experiencing the smell, I then read reports, where others claim to have seen smoke, IIRC). Which I've experienced (along with a bad smell, IIRC), on a number of occasions.So, that 6 watts rating:Quote from: Halcyon on May 06, 2025, 02:17:02 amPossibly increased, to cater for reasonable fault conditions, such as end of (LED bulb) life. When a diode or something, might go short-circuit, and over-load the rest of the circuitry, causing the base to rise in temperature even more than usual.So, they might consider almost all of that 6 watts, going into the base (with a worst-case LED bulb design type, and worst-case efficiency rating), plus various extra safety factors, if they also consider fault conditions, such as end-of-life (LED bulb), component shorts, etc.Hence the lower rating, compared to incandescent bulbs, which don't (usually) have addition electronic components, that might short-circuit at the end of its useful life. Also don't put most of their inefficient heat-generation, into the base, and may be regulated (in the laws of some countries), to have to build in safety fuses.

author: TimFox
author_rank: Super Contributor
timestamp: May 07, 2025, 02:40:11 pm
content: During normal operation, the screw base and “neck” of the glass-envelope incandescent bulb can tolerate a much higher temperature than the base and neck containing semiconductors in the LED bulb.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 07, 2025, 03:39:20 pm
content: Quote from: Psi on May 07, 2025, 10:19:07 amThis is the best advice so far. The rest is just pencil whipping. For example, how in the world do you relate worst case fault mode power dissipation for an unknown design to the nominal operation power rating.

author: tunk
author_rank: Super Contributor
timestamp: May 07, 2025, 03:57:40 pm
content: Maybe they just took a few LED bulbs and measured the sockettemperature and then compared to a 25 watt incandescent bulb?

author: Halcyon
author_rank: Unknown
timestamp: May 08, 2025, 03:25:58 am
content: Quote from: Psi on May 07, 2025, 10:19:07 amIt's just a desk lamp and I was just making an observation which got me thinking, hence the original question. I'm not really looking to change things up, it was just a "huh?" moment.But yes, sound advice for those looking at LED lighting for different applications.

author: EPAIII
author_rank: Super Contributor
timestamp: May 08, 2025, 03:58:36 am
content: I don't know how many people and even how many of the more informed people on this BB realize just how conservative the ratings of things like desk lamps have ALWAYS been. By "ALWAYS" I mean long before the days of LED bulbs.Many of those fixtures have had ratings like 40 or 50 Watts. But we all have put 60, 75, and even 100 Watt incandescent bulbs in them for years. And by "we" I most certainly include myself.Did the average person realize this? NOPE! Even good old, educated me did not really notice such things for many years.I doubt that many houses have burnt down due to this. A shorter life for the fixture? Yes, but this would be measured in years. A shorter life for the incandescent bulbs? Well yes that too. But who really noticed. Frayed cords were and still are a much more dangerous thing.I strongly suspect that the same things will apply to the use of LED bulbs in those same, old fixtures as well as in new, modern ones.If we can invent it, we can f... it up.Quote from: TimFox on May 06, 2025, 08:32:47 pm

author: EPAIII
author_rank: Super Contributor
timestamp: May 08, 2025, 04:26:29 am
content: Use LED strips?Oh great and when they go bad, and they will, just how do you replace them? I have a number of four foot, LED tubes in the same external form as the fluorescent tubes that they are intended to replace. They have LED strips in them. Guess what is failing in a small percentage of them. Some PSU module? NO! It is the strips themselves. Individual LEDs are going bad and at least the designers were smart enough to have a mechanism that bypasses a bad LED so the rest of them still work. The electronics for the tube as a whole are all 100% OK.I recently purchased around 12 track fixtures for better illumination in the bar area of my den. There are track fixtures that do have an integrated design. By "integrated" I mean you can't just replace the bulb, you need to get a new fixture if one goes bad. But with a dozen fixtures in the tracks, you would never be able to buy the same fixture a few years from now and would wind up with either an odd-ball fixture or a bill for another dozen fixtures. That's going to be an expensive replacement if you want things to match.Not going to happen? You should still be able to buy matching replacements for years to come? Really! The church that I attend has 12 large, multiple bulb fixtures that date, I believe from when it was built. They expanded the seating and needed one more, matching fixture for the additional area. I am sure the contractor ordered the same fixture, probably from the original source. It did come close, but it definitely isn't an exact match. Any number of things can mean that a fixture purchased today will not be a good match for even the same model purchased 5 or 10 years ago.Sorry, I can't afford a new set of fixtures every time one burns out. When I selected my track light fixtures I VERY deliberately avoided the ones where the LEDs were integrated. I bought ones that used the good, old Edison base so just the bulb can be easily replaced.But yes, setting the brightness is probably a good idea. I did buy dimmable LED bulbs and a couple of dimmers to control them. I don't plan to run them at full brightness and, due to the sheer number of them, I doubt that any future user will either.Quote from: Psi on May 07, 2025, 10:19:07 am

author: AVGresponding
author_rank: Super Contributor
timestamp: May 08, 2025, 05:09:32 am
content: Quote from: EPAIII on May 08, 2025, 03:58:36 amThe primary risk is unlikely to be fire, directly. In my experience, what will happen is premature and severe embrittlement of any plastic parts, and if the lamp uses solder to attach the conductors to the cap, this can soften and form around the lampholder contact, and make removal difficult for bayonet fittings, and cause bad contacts (and then potentially a source of ignition) on Edison screw types.

author: Zero999
author_rank: Super Contributor
timestamp: May 09, 2025, 08:20:28 am
content: Quote from: Whales on May 06, 2025, 05:54:12 amI don't think so. A 6W LED is equivalent to much more than 25W incandescent. More like 40W to 60W, depending on the quality and whether it has any other features i.e. high CRI, dimmable etc.I think MK14 is right. Many fixtures don't allow sufficient cooling for LEDs. It's true, it's somewhat dependant on the LED lamp. Some designed for more enclosed fittings are built to tolerate higher temperatures, because they have better heatsinking and 105°C electrolytic or film capacitors, but it's better for the fitting manfucature to err on the side of caution, otherwise they'll get loads of complaints and bad reviews from unsatisified customers.https://www.eevblog.com/forum/chat/wattage-ratings-on-lamp-fixtures/msg5905450/#msg5905450