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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

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    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 at 8:35
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    @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 at 9:03
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    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 at 13:21
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    @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 at 15:13
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    @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 at 1:06
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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".

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    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 at 10:30
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    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 at 11:17
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    "Incandescents love hot places and work better there." - that needs some sort of reference... – Mike Brockington Mar 23 at 11:52
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    @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 at 19:17
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    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 at 19:41
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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.

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    The supplied bulbs are 9.5W, per the manual. – P2000 Mar 22 at 23:22
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    No, this is quite common to see on a modern lampholder. – Mike Brockington Mar 23 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 at 13:42
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    @Mike Brockington I have no idea what statement you are referring to. – Richard O Mar 23 at 13:43
  • 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. – Mike Brockington Mar 23 at 14:59
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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.

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    ...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 at 0:24
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    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 at 15:00
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    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 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 at 20:38
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    @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 at 2:39
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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.

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    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 at 21:18
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    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 at 13:15
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    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 at 21:17
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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.

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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.

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