Heat output?

[Pietro Impagliazzo]

Is heat output directly related to wattage, lamp technology or lumen output?

I'm asking this because I never worked with HMIs and when I had no knowledge about them I thought they did not output heat...

Ok, so let me get to my question:

Does a 575W HMI bulb output heat in a similar amount of a 1000W tungsten bulb? More, less?

:confused1:

 

[Richard Andrewski]

If you're talking about the heat in the beam that you can feel when the light falls on you, that is infrared. Tungsten is high in infrared output and also is why tungsten elements are used in heaters. HMI has very little infrared output as is the same with fluorescent as well. That's why they are known as "cool lights" as opposed to "hot lights" or tungsten type lighting.

The fixture itself gets hot in relation to the amount of heat coming from the bulb. Whatever isn't converted to light is to heat. Which is partly a function of the technology of the bulb and also the current driving it (wattage). Thats one reason an HMI bulb is more efficient than a tungsten is it converts a higher proportion of the wattage to light than tungsten does. Its about 4 to 1 like fluorescent and why I call HMI the fluorescent of hard lights.

Besides the obvious function of delivering the light of the bulb into a usable beam, you can think of the fixture as having a heat sink function for the bulb to keep it alive longer. The larger the fixture, the better the heat sink.

Hope this helps.

 

[Pietro Impagliazzo]

I ask this because I was reading the thread about flash photography and someone was asking if the umbrella could sustain the heat output of a 1200W HMI...

And have worked with open-faced tungsten, the 1000W destroys all diffusors and gels I put near it, it's horrible! Not something It happens when I use fresnel, perhaps because the lamp is behind glass and metal.

So I thought: Does a 1200W HMI lamp emits as much heat as a 1000W tungsten one?

What you said was very helpful Richard, however...

I still don't know how hotter or colder (in terms of temperature, and not color hehe) they are compared to tungsten bulbs.

 

[Pawel Achtel]

A 1000W light will ultimately produce 1000W heat, no way around it. The basic law of preservation of energy seems to get in a way :emote_headwall:

Now, how much useful light you can get out of that depends on luminous efficacy of the light source (see: http://en.wikipedia.org/wiki/Luminous_efficacy )

 

[Pietro Impagliazzo]

A 1000W light will ultimately produce 1000W heat, no way around it. The basic law of preservation of energy seems to get in a way :emote_headwall:

Now, how much useful light you can get out of that depends on luminous efficacy of the light source (see: http://en.wikipedia.org/wiki/Luminous_efficacy )

Thanks Pawel... So I can quote you on that, right?

Anyway, I've been scrounging this article for quite some time now but haven't found the answer until now.

And thank you Richard.

 

[Ryan Patrick O'Hara]

A 1000W light will ultimately produce 1000W heat, no way around it. The basic law of preservation of energy seems to get in a way :emote_headwall:

Now, how much useful light you can get out of that depends on luminous efficacy of the light source (see: http://en.wikipedia.org/wiki/Luminous_efficacy )

Those are two contradicting statements, are they not? 'non-useful' light is the wasted heat. The heat will vary on the light energy to heat energy ratio.

When power (energy) reaches a lamp, it is released in two forms... light and heat energy. Different kinds of lamps produce different ratios of heat vs light.

If you are talking about tungsten / black body radiating type sources... they will be pretty much the same as each other... and as you increase thier wattage, the ratio of heat to light remains the same... they get brighter and hotter with the same ratio of output.

If you look at other light sources such as non-blackbody like sources such as HMI's, they convert a much higher percentage of the given energy to light versus heat, but I'm not saying they are not hot! An even better example are Kino's. They turn the small amount of energy given to an overwhelmingly favorable light vs heat ratio. They put out an extremely large amount of light, and little heat. Increase the wattage and eventually they will be HOT, but by that time, the light will be overwhelmingly bright, as the ratio should relatively hold. (not counting heat trapped because of the bulb design and other factors.)

That is my understanding.

So a 650w tungsten will be less hot and less bright then a 1000w tungsten, however the ratio of heat to light output will be the same. Don't quote me on this, but I think tungsten units turn 60-70% of all energy to heat instead of light... which is why HMI's of equivalent wattage put out about 4x more light!... because less of it is going to heat waste.

Therefore, 1000w lights wont always put out the same amount of heat... a 1000w tungsten should waste more energy to heat then a 1000w hmi

 

[ian dart]

hi,
not sure about heat output between hmi and tungsten.

i am sure they all get bloody hot............

when putting anything in front of a light hmi or tungsten i always use the 3 foot or 1 metre rule

for every 1000w = 3 foot or 1 metre

eg. 2k blondie nothing should be closer than 6 feet or 2 metres

i use this especially for glass or windows as having a light to close the heat can cause it to crack.
found this out the hard way......3 times actually........

its easy to burn a hole right through a poly if they are any closer.

cheers,
ian

 

[Pawel Achtel]

Those are two contradicting statements, are they not? 'non-useful' light is the wasted heat. The heat will vary on the light energy to heat energy ratio.

No. All of the power supplied to the light bulb will be turned into heat, whether in the fixture or when it falls onto the subject. It is just that some lights will produce more visible light spectrum than others. :ihih:

 

[Ryan Patrick O'Hara]

No. All of the power supplied to the light bulb will be turned into heat, whether in the fixture or when it falls onto the subject. It is just that some lights will produce more visible light spectrum than others. :ihih:

Ah, ok, we are talking about the same thing. The lighting unit turns the energy into either light or heat energy immediately, and that can differ in ratio.... but yes, the light will eventually turn to heat energy, right?

But that would make the light fixture less hot... If a light initially turns much more wattage to light, that light which turns to heat energy happens elsewhere (not inside the lamp head) then it is less hot... yeah?

So yes a 1000w light will eventually turn all its wattage into a form of heat energy the same as a less efficient 1000w light, but the more the unit can turn the initial energy to light the less heat is at the actual source... making it not as hot. It simply gives the heat away, versus keeping it around the source.

Yes?

 

[Pawel Achtel]

If you want less heat, the answer is simple: use less power (watts).

If you want same light output and less power, you need to use more efficient light source (with highest luninous efficacy).

Replacing 1000W incandescent light with 1000W HMI is not going to produce less heat, but replacing a 1000W incandescent light with a 575W HMI is going to produce less heat: exactly 425W less.

 

[Richard Andrewski]

I ask this because I was reading the thread about flash photography and someone was asking if the umbrella could sustain the heat output of a 1200W HMI...

Not unless the specs of the umbrella specifically say that it can withstand the 1200w of heat because the HMI will need to be very close to the umbrella to do any good. They typically don't give ratings on most umbrellas because they are mostly made for flash photography which has almost no heat output. Using an umbrella with any continuous lighting besides fluorescent is "iffy" in my opinion. Most of them are so fragile unless specifically made to work with hot continuous lighting.

 

[jbeale]

If you want less heat, the answer is simple: use less power (watts).

If you want same light output and less power, you need to use more efficient light source (with highest luminous efficacy).

Replacing 1000W incandescent light with 1000W HMI is not going to produce less heat, but replacing a 1000W incandescent light with a 575W HMI is going to produce less heat: exactly 425W less.

This is quite true if we are talking about total heat in the studio, for example, if you are calculating the load on the A/C system. But specifically about the umbrella, you will certainly have less heat as convection directly from the fixture housing with the 1 kW HMI than 1 kW tungsten, because much more of the total energy output is visible light. However, all this may be an academic distinction if you're using an umbrella designed only for photo strobes; it would likely burn even with the HMI.