Would a 70w halogen bulb produce less heat than 60w normal bulb?

[questionboy]

On Light bulb appliances there is often a 60w limit. I would guess that a halogen bulb of 70w would produce less heat so should be fine to put in similar fittings.

 

[russ_watters]

60W and 70W are both energy outputs, so no, 70W is more than 60W.

 

[Antiphon]

It will produce more light and less heat (IR) but it will produce 10w more as the total sum of visible and IR power which may heat or may not result is a hotter fixture. It depends on how much of the energy is captured by the fixture instead of radiating out.

 

[256bits]

On Light bulb appliances there is often a 60w limit. I would guess that a halogen bulb of 70w would produce less heat so should be fine to put in similar fittings.

You should access and read the following two sites, both of which are informative about light sources:
http://en.wikipedia.org/wiki/Incandescent_light_bulb
http://en.wikipedia.org/wiki/Luminous_efficacy#Overall_luminous_efficacy

There you will find out that for a thermal radiator such as the incadescent bulb the theoretical luminous [efficacy] is 95 lumens per watt, or about 14%, but this is at a temperature of 6300 C. For a typical tunsten bulb, where the filament remains solid, (below 3683 kelvins), most of its emission is in the infrared and the overall luminous efficiency is about 2%.

From the wikapedia article, the halogen lamp operating at 230 v , 100 W, would have an overall luminous efficacy (lm/W) of 2.4 % versus that of a regular incadescent of 2%. This means that this halogen bulb gives out about 20% more visable light, with the same power input.

Your two bulbs operate at 60W and 70W.
Using the above figures as a rough guide ( you would have to consult manufacturer fact sheets to obtain actual figures for voltage, wattage )
60W x 98% = 58,8 watts is given off as heat or not visable em radiation.
70W x 97.6 = 68.3 watts as heat or non visable em radiation.

The 70 W halogen gives off more heat than the 60 W regular incadescent.

 

[willem2]

You should access and read the following two sites, both of which are informative about light sources:
http://en.wikipedia.org/wiki/Incandescent_light_bulb
http://en.wikipedia.org/wiki/Luminous_efficacy#Overall_luminous_efficacy

There you will find out that for a thermal radiator such as the incadescent bulb the theoretical luminous [efficacy] is 95 lumens per watt, or about 14%, but this is at a temperature of 6300 C. For a typical tunsten bulb, where the filament remains solid, (below 3683 kelvins), most of its emission is in the infrared and the overall luminous efficiency is about 2%.

But you don't want the luminous efficiency, because that accounts for the sensitivity of the human eye, which is irrelevant here. You only want to know what percentage of the energy
is radiated away, and not stopped by the glass, or the fixture. This will include lots of
red light, for which the eye is not very sensitive, and some infrared as well.

 

[Studiot]

Exactly, Willem.

A similar miscalculation by manufacturers of the newer LED lighting has lead to building fires and a change of building electrical codes (in Europe at least).

A further comment.

The higher the element temperature the more visible light you get per watt input.
Tungsten is used as the element because it has the highest known melting point of all conductors.
The higher the temperature of the tungsten element the more it evaporates off tungsten atoms.
These coat the inside of the bulb and darken it, reducing the light transmission. This also reduces the life of the element.
So the actual element temperature is an engineering compromise between useful life and output.

Introducing halogens into the bulb's atmosphere partially suppress these evaporated atoms, allowing the compromise to be shifted towards a higher temperature and more light per watt.

 

[russ_watters]

...er, note though, guys, that all of the light energy is heat energy too. It's all just different frequencies of the same thing and ultimately, the 70W lamp adds 70W of heat to the room.

 

[Studiot]

70 watts is 70 watts, yes.

But to the room?

There is a practical difference between 70watts spread throughout the room and 70 (or a bit less) confined to the solid fitting and concentrated near some flammable building component.

 

[I like Serena]

I believe the OP's question is whether a 70 W halogen bulb can be put in a 60 W appliance fitting.
As yet there is no answer.
However, from the posts I've seen here, I would tentatively conclude that one shouldn't.

 

[Studiot]

I believe the OP's question is whether a 70 W halogen bulb can be put in a 60 W appliance fitting.
As yet there is no answer.
However, from the posts I've seen here, I would tentatively conclude that one shouldn't.

I think this is one of those situations where it is a case of

"If you don't know the answer then don't do it"

Halogen lamps are run at higher temperatures than standard.

This means that the lampholder will experience higher temperatures.

This is why halogen lamps are (should be) fitted only into ceramic holders and the immediate connecting leads should have a high temperature cover.

So it is not only a question of wattage.
You should not (in general) use a 25 watt halogen lamp in a fitting designed for a standard 60 watt lamp.
Many fittings designed for standard lamps are made of or contain plastic, unsuitable for use at the temperatures encountered in a halogen lamp.

 

[Naty1]

Post #7 is the correct theory: no matter how you slice it, a 70 watt bulb is consuming more electrical power than a 60 watt bulb since those are measures of power consumption...not direct measures of light production or efficiency. Whether the heat [power] consumed is given off via conduction, convection or radiation, it IS given off.

So I think Studiot and Serena have the correct final conclusion.

 

[Studiot]

Hello Naty, let us be more dramatic about the answer since I say it is also a question of temperature as well as wattage.

Suppose we had two lamp fittings

1) A conventional fitting with plastic insulating parts and a 60watt bulb

2) A 'special' fitting with insulating parts made of ice (yes ice) and a 5 watt bulb

Which would fail first?

 

[cmb]

On Light bulb appliances there is often a 60w limit. I would guess that a halogen bulb of 70w would produce less heat so should be fine to put in similar fittings.

In practice, I suspect it will make no difference, especially if the fitting is 'all metal' rather than some cheap plastic affair. I have desk lights with a '60W' sticker on them, but that is really implying not to put a 100W in there (that being the next size up, for the incandescent bulb range to which it is referring). With a proliferation of new bulb technolgies and varying power outputs, chances are that it will make not the blindest bit of difference, even more so if the bulb in question is a 'spot/reflector' bulb.

The other thing not mentioned here so far is that the physical size of the equivalent halogen is now typically smaller. The fitment rating for an incandescent bulb would, I am quite sure, also take into account the physical size of the bulb within the envelope of the fitting. With halogen types being physically smaller, the convection is much improved within the light fitting, again suggesting that a '60W' fitment rating may be looked upon with a degree of 'flexibility' with the new range of power ratings.

Bear in mind also that such power ratings are unlikely to produce an outright 'hazard', simply that higher powers result in higher surface temperatures, and at some point someone has made a judgement call as to how hot they are permitting surfaces to get before it raises a 'burn-injury' risk. One might expect some margin has been built into that decision.

_{Disclaimer; we cannot see nor know what you have, nor the engineering design margins on it, so what you choose to fit to what fitting is your call, and yours alone.}

 

[Studiot]

Bear in mind also that such power ratings are unlikely to produce an outright 'hazard', simply that higher powers result in higher surface temperatures, and at some point someone has made a judgement call as to how hot they are permitting surfaces to get before it raises a 'burn-injury' risk. One might expect some margin has been built into that decision.

Try reading the information supplied in this thread again and see if you still feel this way.

 

[cmb]

You should not (in general) use a 25 watt halogen lamp in a fitting designed for a standard 60 watt lamp.

I'll not counter you directly on that, but I have never heard of such a caution ever being made. Do you have a link to some consumer/safety website, or such, that puts forward this caution?

There is a caution on the type of switchgear you need to run such bulbs. You generally need twice the equivalent rating for a switch, because of the initial high current loads of the halogen.

Consumers will, no doubt, make up their own minds on this, so without clear information you'll get comments like mine, and like Studiot's in conflict.

I'm not so sure about the 25W versus 60W thing though. This sounds unlikely. For sure, the filament itself runs hotter, but we are talking about an amount of power feeding into an envelope and then a flux of that energy coming back out of it. If the two envelopes are the same size and the same energy flux (notwithstanding the discussions on the spectrum content, as above) I don't see why either would be much different to the other in regards heating of the immediate surroundings.

 

[cmb]

Bear in mind also that such power ratings are unlikely to produce an outright 'hazard', simply that higher powers result in higher surface temperatures, and at some point someone has made a judgement call as to how hot they are permitting surfaces to get before it raises a 'burn-injury' risk.

Try reading the information supplied in this thread again and see if you still feel this way.

I did. Which bit do you think impacts that conclusion?

 

[Studiot]

cmb, you seem to focus on heat input alone.

1) The smaller the bulb the smaller the surface area to effect heat transfer to the surroundings tending to reduce its rate.

2) Filaments in halogen lamps run at considerably higher temperatures than standard. Actual figures are already given here by others. Since the filament is hotter the surrounding lamp internal atmosphere will be at a higher temperature, as will its envelope material.

3) Newton's law of cooling tells us that the higher temperature promotes more rapid heat transfer.

4) Regardless of the rate of heat transfer contact with a body above its softening or melting temperature will eventually destroy insulation. (By the way what lampholders do you know that contain only metal parts?). Hence my ice (an insulator) example.

So there are some competing effects in respect of the rate of cooling, but the issue of heat damage to insulating material is absolute and still occurs with conventional bulbs in non-ceramic insulators.

 

[cmb]

cmb, you seem to focus on heat input alone.
...
3) Newton's law of cooling tells us that the higher temperature promotes more rapid heat transfer.
...

Right, but there is an equivalently 'less of' a halogen bulb. Newton's rate of cooling doesn't describe that you'd have twice the heat flow for twice as much stuff.

If you were to draw a bubble around the bulb with a total surface area of 100cm^2 and you stick 100W into it and it attains thermal equilibrium, then I do not see how it matters at all whether that 100W has been used to heat something to 80C or to 10,000K, because you will still have 1 W/cm^2 heat flux from it.

The consequence of the 'spectral temperature' difference is accounted for above - we're talking 97.6% of the total heat flux under consideration for a halogen, compared with 98% for an incandescent. I'm generally discounting that as being essentially a statistical irrelevance, compared with all the other unknown variables in the OP's light fitting.

So, I don't comprehend what you are saying. Why does a thermal flux of 1 W/cm^2 from one bulb differ to 1 W/cm^2 from another?

 

[Studiot]

Why does a thermal flux of 1 W/cm^2 from one bulb differ to 1 W/cm^2 from another?

Because the heat is being produced by sources of different temperatures.

The problem is not with the heat dissipated to the general surroundings (the room) but the temperature of the heat source in intimate physical contact with very local surroundings (the holder) and its effect on the temperature sensitive parts of that holder. Yes the heat passes through the holder and onto the general surroundings, but what damage does it do on the way?

 

[cmb]

Yes the heat passes through the holder and onto the general surroundings, but what damage does it do on the way?

So, if you're saying that you need to run a 25W halogen in place of a 60W incandescent, and that it is because of heat conduction up the bulb stalk, then how much power are you saying is going up the stalk in each case?

You should not (in general) use a 25 watt halogen lamp in a fitting designed for a standard 60 watt lamp.

Do you have a reliable source for this assertion? It just sounds very wrong to me.

 

[russ_watters]

Several things here...

1. It is morning and when I suppose I didn't even read the OP, just the title and responded to the title only in my first post.

2. I've often ignored lamp size warnings, but wouldn't recommend others do it (not that I'd chastise others for it either...).

3. There is more than one type of halogen lamp, so some of the differences of opinion here are based on on different assumptions about the physical differences (if any) between the halogen and the normal incandescent. Typically, a theoretical question assumes all other factors are equal except the one you are asking about while a real-world question may have additional stipulations. This may be such a case. So we have to treat it two different ways:

Case A: If two lamps are physically identical in dimensions, then the surface temperatures must be similar. Since the vast majority of the heat loss is radiated or convected from the surface due to the temperature of the surface (as per the efficiency calcs done earlier in the thread), similar heat loss must mean similar temperature. So how can a halogen be hotter and the same temperature at the same time? Simple: by putting a hot lamp inside a standard lamp: http://en.wikipedia.org/wiki/File:Wolfram-Halogenglühlampe.png
And since the outer lamp is about the same temperature, the base must be at about the same temperature, since it conducts heat from the outer lamp.

So: A 60W halogen would have a surface temp slightly cooler than a 60W standard due to the higher efficiency, but the 70W halogen is not enough more efficient to also have a lower temp -- again, as per the efficiency calcs above.

Case B: The two lamps are not physicall identical. Well then all bets are off. Halogens are often phsyically smaller because they have to be to run hotter unless they have a second bulb wrapped around them (as in the link above), so in those cases they will have a higher surface temp... but then, they also could be insulated to protect the fixture: https://www.amazon.com/dp/B000SMQ3QU/?tag=pfamazon01-20

 

[russ_watters]

Lemme try to be more concise:

Most of the confusion here seems to stem from Studiot's assumption that the halogen will be physically smaller than the standard, which is not necessarily true.

 

[Studiot]

Most of the confusion here seems to stem from Studiot's assumption that the halogen will be physically smaller than the standard, which is not necessarily true.

Where did I say that?

If I did I am sorry because I agree it is not true.

However your other line of reasoning needs revising since there are other factors, besides heat flow determining the element temperature.

 

[Studiot]

So, if you're saying that you need to run a 25W halogen in place of a 60W incandescent

I didn't say that.

What is true, and I assume you know, is that both standard tungsten and incandescent lamps provide light by the same mechanism - both contain an incandescent tungsten element. The halogens do not provide any light, they do not function as the gasses do in a flourescent source.

and that it is because of heat conduction up the bulb stalk, then how much power are you saying is going up the stalk in each case?

As a physicist you surely understand that different arrangements of different substances may well have different rates of internal heat transfer?

Again the truth is: heat transfer throttling is one way to maintain a steady state temperature differential between two parts of a body.

 

[russ_watters]

Where did I say that?

If I did I am sorry because I agree it is not true.

However your other line of reasoning needs revising since there are other factors, besides heat flow determining the element temperature.

Really? So are you instead saying that two bulbs of identical dimensions and heat outputs can have different temperatures?

The things you are saying appear to me to contain either inconsistencies or hidden/implied assumptions...so I went for implied assumptions first.

 

[Studiot]

So you're saying that two bulbs of identical dimensions and heat outputs can have different temperatures?

No I am saying that not only can different parts of a body be at different temperatures in a steady state, but that it is a common well known phenomenon. All that is required is that there be a throttling or limiting section between two (or more) parts of the body that control the heat flow. Further I am stating that this is the case with the humble light bulb.

Most of my input to this thread has been confined to safety considerations, taken from current codes and best practice. However there is much useful and interesting physics behind lighting technology that deserves a good airing.

 

[russ_watters]

The "different parts" being the base and the bulb?

 

[cmb]

Looks to me like Studiot has confused 'temperature' with 'heat'. The filaments of both a 'conventional' bulb and a 'halogen' bulb can be at different temperatures, but hold the same heat and(/or) derive the same heat flux (electrical energy into thermal out).

The main difference in mechanical terms is that the halogen 'bulb' is usually a very small volume envelope, because [one presumes] it is the best arrangement to promote the tungsten back onto the filament (as is the particular 'trick' needed to get the filament running hotter and for it to survive). As it is small, of course (by the 'heat flux' through a smaller area) it gets very hot indeed, so much so that some form of quartz is used, rather than glass. It gets so hot that it is a risk to handle it directly because, apparently*, the grease of your fingers alone can boil and rupture the primary envelope. That's why a second envelope of glass is used, for these 'substitute' bulbs to replace regular ones.

*(uncited - not sure if that is an urban myth, but it sure goes wrong if the quartz enclosure gets dirty)

So I think that's the basic conceptual issue here - a halogen bulb has a hotter filament, but the filament has much the same heat as that in an incandescent bulb.

 

[russ_watters]

Let me identify specifically what I take issue with:

2) Filaments in halogen lamps run at considerably higher temperatures than standard. Actual figures are already given here by others. Since the filament is hotter the surrounding lamp internal atmosphere will be at a higher temperature, as will its envelope material.

That is not true. First, some have a lamp-in-a-lamp design, but second, a higher bulb temp means more heat transfer and more wattage. You can't have a higher temp for the same size bulb and the same wattage. As a result, a higher filament temp for the same wattage must mean a physically smaller filament and therefore the same gas and envelope temp.

4) Regardless of the rate of heat transfer contact with a body above its softening or melting temperature...

Rate of heat transfer is a function of temperature. You can't separate them like that.

 

[Studiot]

All very interesting, but also at odds with what can be found on a simple google search on 'filament temperature'. How do you think the filament in a halogen source achieves its different colour temperature, if it is at the same temperature as the one in a standard bulb?

I do not have more time to waste on this as I am leaving the country, but I wish all and sundry the greetings of the season.

 

[cmb]

How do you think the filament in a halogen source achieves its different colour temperature, if it is at the same temperature as the one in a standard bulb?

No-one has said it would be at the same temperature. Quite the opposite.

But it might be as 'hot' as a filament in a standard bulb, that is; same J, different K.

You seem to be labouring under the impression that the filaments would be the same size. Just figure that the incandescent one is twice the size of the halogen one... same heat flux, but arising from twice the differential temperature!...

 

[Vanadium 50]

CMB, this is much simpler than you are trying to make it, partly because many of your "facts" are not.

Halogens and ordinary incandescents operate at the same filament temperatures, around 3300K.

70W goes into the bulb. Energy is conserved, so what is not converted to light becomes heat. The fraction of energy converted to light is between 2 and 2.5% for both ordinary and halogen incandescent bulbs. So the 70W bulb produces something like 15-18% more heat than the fixture is designed to handle. Full stop.

Your suggestion that it is safe to exceed the posted limit because surely someone somewhere put in a safety margin is irresponsible and dangerous.

 

[AlephZero]

Most of #13 - #31 seems to be a (fairly hypothetical) discussion of the normal operation of the lamps.

Safety ratings are about abnormal situations, whether accidental or "deliberate but misguided". As V50 implied, in a worst case situation (e.g. all cooling airflow around the bub is blocked off) the only thing that matters is the total heat output from the lamp.

 

[cmb]

CMB, this is much simpler than you are trying to make it, partly because many of your "facts" are not.

Halogens and ordinary incandescents operate at the same filament temperatures, around 3300K.

Really?

(Why have you singled me out for that comment, when I was neither the first nor the last to make it?)

Your suggestion that it is safe to exceed the posted limit because surely someone somewhere put in a safety margin is irresponsible and dangerous.

I did not make that association '..because..'. That is falsely attributing something to me that I did not say. I made it clear that a '60W' rating is making it clear that a '100W' bulb is unsuitable, that being the next power rating up, and that the consumer should be cautious over using 'similar' ratings in the new technology but that it is unlikely to make much difference.

Please quote from my text where I said "...it is safe, because there is margin...", or otherwise acknowledge your misreading of my posts.

In fact, to make it easier for you, please quote anywhere where I have used the word 'safe'.

 

[cmb]

Most of #13 - #31 seems to be a (fairly hypothetical) discussion of the normal operation of the lamps.

Generally, that is so, but it still presents a real and present issue because, e.g., in the UK light fittings still all generally say either 'use 60W bulb' or 'use 100W bulb'. The problem is that you can no longer buy bulbs with those power ratings. The nearest equivalents to 60W, for example, are 70W (equivalent to '95W' worth of incandescent) or 35W (equiv to 45W). So, for an equivalent application, the former is technically too much power, the latter is typically too dark for the application.

So an unsupported comment like Studiot's, from which the #13-#31 series ran, [that 25W halogen should not be put in 60W regular fitting] is unhelpful.