14

I recently replaced a ceiling light fixture with a ceiling fan with two light sockets that have a maximum rating of 9 W for LED bulbs. The bulbs in the original fixture are 10 W LED and dimmable. The bulbs that came with the fan are non-dimmable. Can I use the 10 W bulbs in the 9 W max socket? My understanding is that heat is the main reason for the wattage rating, but does 1 W make that much of a difference? That’s barely 0.01 A if I’ve done my math correctly.

Both bulbs are 60 W replacement bulbs. The 10 W is a Satco S9703. The 9 W is an Ecosmart (I think it’s this). Fan is a Hampton Bay Rothley II 52050

Peter Mortensen
  • 333
  • 2
  • 8
linux2647
  • 151
  • 1
  • 1
  • 5
  • 1
    if the light is open on top and not a globe it should be fine; heat can escape. Worst case you reduce the bulb life; 1w isn't enough to start a fire or anything... – dandavis Mar 22 '21 at 01:31
  • 17
    You say it has "Maximum rating of 9W for LED bulbs" Does it have a rating for incandescent bulbs? I've seen things rated 60W Incandescent / 12W LED, which is clearly nonsense. – SiHa Mar 22 '21 at 08:35
  • 8
    @SiHa not necessarily, LED heat tends to be hot at the base and dissipated by convection whereas incandescent is hot at the filament and dissipates by radiation – ratchet freak Mar 22 '21 at 09:03
  • 1
    In particular (as @ratchetfreak implies) a poorly-ventilated fitting with the lamp base at the top tends to run the electronics rather hot. Running hot will shorten the bulb life, probably not by much unless it was run at close to its limits already – Chris H Mar 22 '21 at 12:24
  • 4
    Heat is proportional to power, not current, so "0.01 amps" doesn't mean much of anything if your concern is overheating. – Phil Frost Mar 22 '21 at 13:21
  • Anecdotally, I have a desk lamp (probably 15 years old at this point) which has 60 watts max rating. Works great with 9 watt LEDs but as soon as I put in a 13 watt LED it will not power on at all. You may experience something similar in your situation. I do not claim to understand the inner workings nor safety features but it seems like the manufacturer has prevented me from starting a fire. Yes, the bulbs work fine in ceiling fixtures. – MonkeyZeus Mar 22 '21 at 14:22
  • 10
    @ratchetfreak It's maybe been long enough that personal experience with incandescent bulbs is waning, but I guarantee you that the base of an incandescent 60W bulb gets MUCH hotter than a 10W LED bulb. The heat from a LED bulb is concentrated in its base, yes, but the total quantity of heat it is shedding is still much lower. – J... Mar 22 '21 at 15:13
  • 2
    @J... this makes sense when you are trying to not destroy the fixture. But... in a fixture that can take the heat from a 60W incandescent simply by being thermally resilient, rather than providing good cooling, a 60W LED bulb would be cooked dead in short order. – rackandboneman Mar 22 '21 at 22:52
  • 3
    @rackandboneman That's a pointless statement. – J... Mar 22 '21 at 23:00
  • Have you looked for a 9W bulb with the same lumen output as the 10W bulb you're wanting to use? – ThreePhaseEel Mar 23 '21 at 00:15
  • 8
    @J... they are unrelated goals. It's OK for an incandescent to get hot - not OK for it to set other things on fire. LEDs don't set things on fire, but it's not OK for them to get hot. These thermal objectives are totally unrelated, so there will be no connection between a fixture's incandescent rating and its LED rating. – Harper - Reinstate Monica Mar 23 '21 at 01:06
  • @Harper-ReinstateMonica Yes, my point exactly, albeit more eloquently expressed. – J... Mar 23 '21 at 01:19
  • Accept Harper's answer, that is the best one. You have to know what each limitation is attmepting to achieve. – Neil_UK Mar 23 '21 at 05:46
  • 1
    @PhilFrost Heat is perfectly proportional to current. At constant voltage (which is the case here) watt and ampere are trivially convertible between each other (and the OP did just that). – Peter - Reinstate Monica Mar 24 '21 at 23:39
  • @rackandboneman Have you ever experienced a household LED going out on you? I haven't had any long enough to see that yet. If "cooked dead in short order" for an LED bulb means it's going to last only 6,000 hours instead of 30,000 then so be it. Fine. See you in 10 years. – Peter - Reinstate Monica Mar 24 '21 at 23:44
  • @Peter-ReinstateMonica "Heat is perfectly proportional to current." Only if everything else remains constant. If things start varying according to temperature and/or voltage in a non-Ohmic relationship, that's no longer true. – nick012000 Mar 25 '21 at 03:13
  • @nick012000 Unless the voltage changes (which it doesn't in this scenario) I couldn't care less about anything varying: The heat stays perfectly proportional to the current (which surely may change, sure). – Peter - Reinstate Monica Mar 25 '21 at 09:27
  • @Peter-ReinstateMonica I have seen household LED bulbs fail, yes. But, what I was hinting at is what would happen if you put a LITERAL 60W LED bulb - not a 60W equivalent - in a fixture designed for a 60W incandescent. – rackandboneman Mar 25 '21 at 16:03
  • 1
    @rackandboneman Need some serious light there, don't you :-). Yes, that can go bad very quickly. I'd be surprised if such a bulb were available at all, for that very reason, actually: No normal fixture is suited for such a bulb. The seller would make themselves liable for fires. As an aside, few people would need it (the same way few people needed 600W incandescent lights). – Peter - Reinstate Monica Mar 25 '21 at 16:29
  • @Peter-ReinstateMonica not that kind of light :) But I did get the joke I think. – rackandboneman Mar 25 '21 at 16:31
  • @Peter-ReinstateMonica Yes, you can calculate power from current, if you know some other variables. But to perform any thermal calculations you need to know power, so calculating current in this case is utterly pointless. We already know they are 10W bulbs, that means 10 joules per second of thermal energy that has to go somewhere. It doesn't matter if that 10W came from 0.1A or 1000A: it's the same heat either way. – Phil Frost Mar 29 '21 at 13:22

6 Answers6

31

There are two completely different thermal objectives

First, don't set other stuff on fire. That's decided by the thermal insulation of the fixture (think: thick insulation in down lights) and limits the size (in actual wattage) of any bulb, but it's mainly aimed at incandescents. Incandescent bulbs love hot places and work better there.

A fixture succeeds at this goal if it has plenty of insulation and creates a little "oven" for the incandescent to burn in.

Second, let the LED keep cool. The LED cannot tolerate high temperature - neither at the LED proper or the electronic driver. Its worst worst enemy is itself: even with their good efficiency, still nearly 85% of its actual wattage is turning into heat at the LED or driver. The heat will cause premature failure of the LED.

A fixture succeeds at this goal if it provides an easy way for heat to be convected away from the bulb location.

These objectives are at best unrelated, and at worst conflicting. For instance a well-insulated, embedded-in-ceiling downlight might protect from incandescents but cook LEDs. An antiquey lamp with "lamp chimneys" might work great to convection-cool LEDs, but with incandescents, scorch the ceiling above it.

The fixture's LED limit applies to the second thermal objective. It is saying "Above 9 watts, we can't guarantee we can keep that LED cool enough for it to have a long life".

Harper - Reinstate Monica
  • 300,628
  • 26
  • 286
  • 734
  • 4
    What do you mean by “nearly 90% of its actual wattage is turning into heat”? Certainly, energy loss to heat for LEDs is much lower. – bodo Mar 23 '21 at 10:30
  • https://www.ledsmagazine.com/leds-ssl-design/thermal/article/16696536/fact-or-fiction-leds-dont-produce-heat quotes 85% for heat, 15% for visible light (still 3x as efficient as incandescent). Not sure if that's for just LED or LED+driver in a package (aka led bulb). I would be interested in a proper explanation. I do see drivers and to some degree LEDs getting hot/warm, so there's definitely heat leaking. – domen Mar 23 '21 at 11:15
  • 4
    9W LED has ~800 lm. 600lm = 1W (give or take. It is wavelength dependent so it depends on spectrum). So, this LED is 15% efficient. There are more efficient LEDs but those tend to be quite expensive. – Zizy Archer Mar 23 '21 at 11:17
  • It needs to be pointed out that LED and incandescent bulbs might have different "set on fire" limits - after all, LEDs have heat concentrated in base unlike incandescent bulbs which radiate most of heat away - so the base might get too hot for the fixture to handle safely even if total power draw is lower. But I guess any fixture that can take 60W bulbs will be able to safely handle at least 15W LED. – Zizy Archer Mar 23 '21 at 11:32
  • 5
    "Incandescents love hot places and work better there." - that needs some sort of reference... – MikeB Mar 23 '21 at 11:52
  • 1
    @domen I'm a bit skeptical about the numbers quoted in that article. The equivalence numbers for LED bulbs indicate that they're about 6x as efficient as incandescents, not the 3x between the typically 15% and 5% figures in the article. FWIW the 5% number is familiar to me from prior reading. – Dan Is Fiddling By Firelight Mar 23 '21 at 11:53
  • @ZizyArcher The Dubai Lamp is probably the best example. They've mandated a minimum efficiency of 200lm/W there by law and, as the name suggests, though, they're hard to find outside of Dubai. And pricey. The 40W equivalent there is only 2W, and the 60W equivalent runs at 3W. – J... Mar 23 '21 at 14:50
  • 1
    @domen "ledsmagazine.com/leds-ssl-design/thermal/article/16696536/… quotes 85% for heat, ..." - That article is from 2005, LEDs have improved since then. As a single data point, consider the €1 Ikea Ryet LED bulb; specced at 470lm @ 4.5W, for 104lm/W. Optimal is about 340lm/W, so those cheap Ikea bulbs are already about 30% efficient. – marcelm Mar 23 '21 at 15:00
  • 4
    @bodo That's your lay impression talking. Your error is assuming incandescents "certainly couldn't have been <2% efficient!" Yeah. They were. – Harper - Reinstate Monica Mar 23 '21 at 19:17
  • 2
    @J... An axiom of LED marketing is to hoodwink you into accepting less actual light... because "enough LED emitters" cost more than lies. A real 60W incandescent is >=800 lm. "60W equivalent" LEDs are typically 440-600 lumens. Better CRI is no help, since the incandescent was 100% CRI. – Harper - Reinstate Monica Mar 23 '21 at 19:28
  • 6
    Incandescents are 8-16 lumens per watt depending on size (smaller = less efficient because they have to reach their target temperature to function at all). Perfect is 683 lm/w. While some raw LEDs have some impressive lm/w figures, that ignores driver losses, which become a larger piece of the pie as LEDs get more efficient, and the mere existence of hyperefficient LEDs does not mean they are readily available. – Harper - Reinstate Monica Mar 23 '21 at 19:41
  • 2
    @Harper-ReinstateMonica If you're interested, I believe the Dubai spec lamps achieve their efficiency by increasing the number of LEDs in the bulb and running them below their rated output. LED power consumption goes as the square of the voltage but light output is linear with same (ie: half the light needs only 1/4 the power). It means you need 2-4x the LEDs in the module, at higher cost, but the total module efficiency goes up. CRI is 80 for the Dubai lamps, which is reasonable. For an oil kingdom with indoor ski hills in the desert, though, it seems a weak greenwash overall... – J... Mar 23 '21 at 20:54
  • Comments are not for extended discussion; this conversation has been moved to chat. – BMitch Mar 25 '21 at 00:23
17

I think you misunderstood the instruction manual. Where it reads "LED bulbs (9-Watt, Maximum)" is in the parts list. This is not giving the fixture rating. It is saying that the included lamps will use a maximum of 9W. As the manufacturer may source the lamps from multiple vendors, this makes sense.

You will need to look at the fixture to determine the actual rating. There should be a sticker or stamping with the information.

Richard O
  • 171
  • 4
  • 4
    The supplied bulbs are 9.5W, per the manual. – P2000 Mar 22 '21 at 23:22
  • 1
    No, this is quite common to see on a modern lampholder. – MikeB Mar 23 '21 at 11:49
  • @P2000 I was unable to find where that is stated. I did follow the product link to the Home Depot site and then searched the manual linked from the product page. In any event, my advice in the second paragraph still stands. – Richard O Mar 23 '21 at 13:42
  • 1
    @Mike Brockington I have no idea what statement you are referring to. – Richard O Mar 23 '21 at 13:43
  • 1
    The lamp on my desk a foot away from me has a sticker on it, just below the actual lamp-holder socket, which says: "Max 60W E27 GLS / Max 11W E27 CFL" each line being followed by a symbol for that type of bulb. If I go into B&Q, most of the lamps and shades will have similar, clearly displayed, markings. These are warnings, not ratings, since bulbs are sold separately. – MikeB Mar 23 '21 at 14:59
10

The maximum power ratings are set by the design of the fixture. If it says 9W max. then you run a risk or damage or fire by exceeding that. Going from 9 to 10 W is a GREATER than 10% increase.

jwh20
  • 23,250
  • 2
  • 32
  • 65
  • 3
    ...and dimmable 9W (or less) LED bulbs are easily available for not much money. Nothing is forcing you to use the bulbs that came with the fixture OR the bulbs in the fixture you are replacing - put those somewhere else suitable. – Ecnerwal Mar 22 '21 at 00:24
  • 5
    Just for the record, "GREATER than 10%" here means "11.1%". I suggest being clearer about the position you are taking. Are you saying that with a 10W bulb it might actually catch fire, or our you saying that if we admit it is still well within the margin of safety, someone will get the idea that the limits mean nothing. – David42 Mar 22 '21 at 15:00
  • 4
    I'm saying if the manufacturer of the device said "9W max" they very likely had a good reason for that rating. – jwh20 Mar 22 '21 at 15:44
  • @David42 Its unclear to me what jwh20 is actually saying is more than a 10% increase. Power usage? Chance of damage or fire? Your numbers are right for power usage but the chance of damage or fire isnt proportional to power. Which is probably the number people really care about. – Matt Mar 23 '21 at 20:38
  • 2
    @Matt You are right, he could be more specific. Still, I doubt there is a linear relationship between input power and fire danger. If fact, the actual increased danger is likely to be zero since both 9W and 10W are surely well within what should be a generous margin of safety. And that brings us to the problem with this answer. It is a legalistic response to a request for a frank answer, but is not clearly identified as an attempt to reframe. An uniformed reader could come away with the impression that these limits are set just below the point when the fixture will burst into flames. – David42 Mar 24 '21 at 02:39
10

The manual is vague, but I think the trick here is what I like to call "old wattage".

Back in the not-so-dark dark ages of light bulbs, everything was incandescent. Incandescent wattage was important because a light bulb with a 100 watt fillament puts out a LOT more heat than a 60 watt bulb. So if you put a higher watt bulb into many fixtures, it could do things like start fires. As such, you'll see a lot of fixtures rated for, say, "60 watt bulb maximum".

CFL and LED changed the rules because they produced the same lumens (measurement of light) without all that wasted heat. But people didn't learn lumens, they learned "old wattage". They want the same light that a 60 watt incandescent bulb produced. As such, CFL and LED are often labeled in "old wattage". I have a bathroom fixture that says "60 watts maximum", but I have a "75 watt" LED that uses a paltry 11 watts. It works because there's no serious heat generated.

That brings me to your light. It says "9 watt maximum", but that can't possibly be a limit. In order to have a hard 9 watt maximum, it would ridiculously small wiring (1 amp = 120 watts, and most small wires will carry that little easily). I seriously doubt your fixture has wires that small. But if we compare a 9 watt bulb to "old wattage", we find it's really a "60 watt" bulb.

Illuminating with the equivalent of a 60-Watt incandescent bulb but only consumes 9W of power, making these daylight led bulbs one of the best energy efficient lighting.

This now makes sense, because a lot of fixtures (especially fan lights) have labels that say "60 watt maximum". If this were a hard 9 watts, there would be warning labels screaming that fact everywhere.

Machavity
  • 24,720
  • 7
  • 42
  • 93
  • 2
    Agreed, the 60W history is likely the cause of this. And I'd never design line-side wiring to disintegrate at 75mA (9W/120V)... however, OP is formally still stuck with that notice until cleared by the manufacturer or an engineer, as silly as it is. Best to make a call. – P2000 Mar 22 '21 at 21:18
  • 1
    It doesn’t apply to OP but I think 9W incandescent limits could exist: my fridge is 10W limit. Highly unlikely for room lighting, though l. – Tim Mar 23 '21 at 13:15
  • 2
    Unfortunately if you call their tech support line to ask why the 9.5W limit exists you'll get an answer crafted by the legal department. – jay613 Mar 23 '21 at 21:17
7

Whether an LED bulb will be suitable for use in a fixture will generally depend upon two factors: (1) how hot the bulb would get in the fixture, and (2) how hot the bulb could get without adversely affecting lifetime. If a fixture has a 9W rating, that would suggest that a typical 9W bulb may get warm enough to reduce its lifetime somewhat, but not disastrously; the reduction of lifetime would become increasingly severe if power levels go much beyond that, but predicting how far beyond one can go may be affected by many factors and thus hard to predict. A 10W bulb which is never operated at an ambient temperature of over 30C may have its lifetime affected by heat less than would a 9W bulb used in the same fixture when the ambient temperature was 45C.

If one has some 10W bulbs and a 9W fixture, and would have no use for the bulbs other than the fixture, the 10W bulbs would almost certainly work safely for however long they last. The lifetime might be reduced enough to make the purchase of 10W bulbs for such a purpose uneconomical compared with 9W bulbs, but if one has the 10W bulbs and no other use for them, and if one doesn't mind the effort required to replace bulbs when they fail, use of the 10W bulbs shouldn't pose any safety hazard.

supercat
  • 1,058
  • 5
  • 8
6

It's already puzzling out of the box: the manual reads "uses two 9.5-Watt LED bulbs which are included", and the sockets are rated "maximum 9W".

Considering the horizontal position of the bulbs and that the light diffuser bowl is top-open and allows convection, it seems that 10W could be fine.

How the legal line would be drawn if there is a catastrophic failure at such a small margin of difference remains unclear. Strictly, 9W is the maximum, unless the manufacturer can clear you. Call them.

P2000
  • 15,985
  • 30
  • 51