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Author Topic: Brightness & Heat ratio difference between tungsten/halogen vs HMI?  (Read 4990 times)

jazzy

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From what I gather, HMI is about 3 times efficient as tungsten (before daylight balanced), so 575HMI is equivalent to 2K tungsten, is that right?

And is there a simple ratio for heat generated as well?

« Last Edit: April 13, 2016, 03:17:04 pm by jazzy »
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rogan

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #1 on: April 13, 2016, 09:44:32 pm »

From what I gather, HMI is about 3 times efficient as tungsten (before daylight balanced), so 575HMI is equivalent to 2K tungsten, is that right?

And is there a simple ratio for heat generated as well?

Just know in a small studio they get hot fast. And the both take a while to cool down before you can pack them if moving locations. There are other differences. You can turn off a tungsten and right back on without a problem. HMI's if hot, have to cool down for a restrike. 
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UlfKrentz

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #2 on: April 14, 2016, 05:58:05 am »

If you balance tungsten to daylight the difference would be even more. As all the electrical energy is converted to heat you know the answer, HMI is way "cooler". Video lighting is usually not or less force cooled (fan) for sound reasons, so a lamp housing like the broncolor head is getting hotter than their flash counterpart with tungsten modeling light. Nearly all modern HMI are hot restrikeable so no need to wait to get them busy again. They need a few minutes to reach their final color though, also dimming will run them more blue and reduces CRI. Tungsten is a true full spectrum lamp and is superior regarding the light quality. In general avoid to switch HMIs off all the time as the starting process is erosive for the bulbs. HTH.

Cheers
Ulf

jazzy

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #3 on: April 14, 2016, 09:58:19 am »


Hi Ulf,

Regarding heat, I think it might be a little more complicated. Electrical energy is converted into light AND heat. So for the same wattage, the more light you produce the less heat you produce, I think? However somehow I feel my 575W HMI produce more heat than the 650W halogen modelling light, so I'm a little bit confused.


I have another question about balancing tungsten light: what is the difference between balancing at light source (gelling the light) and balancing in camera (with lens filter) and balancing in camera (using sensor temperature setting/setting sensor white balance)? I understand that best practice should be gelling the light, but can we balance in camera sensor (setting to 3200K) to save those 2 stops of light loss?



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AlterEgo

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #4 on: April 14, 2016, 10:07:47 am »

I have another question about balancing tungsten light: what is the difference between balancing at light source (gelling the light) and balancing in camera (with lens filter)

if you gel the light you do not compromise your optics with a filter... certainly that might not be that important for you in your particular shooting scenario, but in some cases various parasitic reflections, etc do matter....

and balancing in camera (using sensor temperature setting/setting sensor white balance)?

by altering the light for example you get achieve better (as in more equal between "RGB" channels for raw data) sensor saturation... but then you might need special "camera profiles" for your converter... if you shoot in raw (but then even w/ JPG you can imagine a more theoretical scenario when gelling the light will result in a less drastic WB math /you do not want to multiply noise, underexposed channel/ for camera raw converter ( = profit )


« Last Edit: April 14, 2016, 10:11:43 am by AlterEgo »
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AlterEgo

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #5 on: April 14, 2016, 10:14:48 am »

but can we balance in camera sensor (setting to 3200K) to save those 2 stops of light loss?
such math can't produce the missing photons ... for example if you have weakish blue part of the spectrum in tungsten light for a start and you shoot something reflecting mostly reddish back then you blue channel in raw will be a mess... multiplication for WB does not make S/N better.
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UlfKrentz

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #6 on: April 14, 2016, 12:21:14 pm »

Hi Ulf,

Regarding heat, I think it might be a little more complicated. Electrical energy is converted into light AND heat. So for the same wattage, the more light you produce the less heat you produce, I think? However somehow I feel my 575W HMI produce more heat than the 650W halogen modelling light, so I'm a little bit confused.


I have another question about balancing tungsten light: what is the difference between balancing at light source (gelling the light) and balancing in camera (with lens filter) and balancing in camera (using sensor temperature setting/setting sensor white balance)? I understand that best practice should be gelling the light, but can we balance in camera sensor (setting to 3200K) to save those 2 stops of light loss?

For the temperature, I thought I addressed that in my original answer. The HMI units are not equipped with a strong forced cooling system (ventilation) and therefore they are getting hotter than their flash counterparts. This is just my guts feeling though… Of course also the increased amount of light output is a problem for egg crates or modifiers that absorb light (resulting in heat), that and the missing ventilation is the reason some strobe modifiers canīt be used with HMI.

White balancing with either gels (get heat resistant gels!) or camera filtration are both good solutions (with the downside of the filter being in the optical system like AlterEgo already pointed out). Filter on camera also adds blue to all lights (including the natural / daylight sources) which can create a great look and is one appropriate and professional way to go. "Software" balancing not so much, while it will look the same on first sight you probably end up in a starved blue channel adding noise and artifacts, but hey, if you donīt have the filters, still better than trying to fix it in post ::).

Cheers
Ulf

Ellis Vener

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #7 on: April 14, 2016, 03:02:53 pm »

From what I gather, HMI is about 3 times efficient as tungsten (before daylight balanced), so 575HMI is equivalent to 2K tungsten, is that right?

Pretty close.

Quote
And is there a simple ratio for heat generated as well?
Are you asking about theory, naked bulbs, or in different fixtures?
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Ellis Vener

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #8 on: April 14, 2016, 03:07:02 pm »



I have another question about balancing tungsten light: what is the difference between balancing at light source (gelling the light) and balancing in camera (with lens filter) and balancing in camera (using sensor temperature setting/setting sensor white balance)? I understand that best practice should be gelling the light, but can we balance in camera sensor (setting to 3200K) to save those 2 stops of light loss?
Gelling individual lights allows you to set the lights for different colors. Sometimes it's good to have a full CTO on one light and a 1/2 CTO (or a straw gel, etc.)  on others.
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jazzy

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #9 on: April 14, 2016, 10:22:30 pm »

@AlterEgo, Ulf: Thank you guys, fantastic answers. I have not seen many people using lens colour filters since the film days but I will have to think about it more seriously, especially for mixed lighting scenarios.

One more question: After daylight-balancing all light sources, if I take a photo of a grey card, should the white balance of the card (using WB picker on software or in camera) read 5500K? What is the best way to know you have got it right?


@Ellis: Lets say naked HMI bulb and naked halogen bulb, both 500W?

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UlfKrentz

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #10 on: April 15, 2016, 04:20:39 am »

@AlterEgo, Ulf: Thank you guys, fantastic answers. I have not seen many people using lens colour filters since the film days but I will have to think about it more seriously, especially for mixed lighting scenarios.

One more question: After daylight-balancing all light sources, if I take a photo of a grey card, should the white balance of the card (using WB picker on software or in camera) read 5500K? What is the best way to know you have got it right?


Just use your usual workflow that works for you. I tend to keep a slightly tint from the original colors, just feels more natural, also remember you can split up filtration between camera and lights.
Have fun!

Cheers
Ulf

GrahamBy

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #11 on: April 15, 2016, 06:30:18 am »

Regarding heat, I think it might be a little more complicated. Electrical energy is converted into light AND heat. So for the same wattage, the more light you produce the less heat you produce, I think?

According to Wikipedia, a typical tungsten light has 2% efficiency, so tripling the efficiency gives you 3x the light (6% vs 2%) and hardly changes the heat output (98% vs 94%). Or the other way around, same light for very close to 1/3 the heat.

https://en.wikipedia.org/wiki/Luminous_efficacy

 
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jazzy

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #12 on: May 26, 2016, 11:22:20 am »


I have another question regarding HMI.

How do I know when the bulb should be replaced?

The counter in my lamp is not working. I can see the colour change slightly and occasionally it might act up a little bit (goes off and goes on right away).

Should I wait for it to fail or it can be damaging to the equipment to do so?
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UlfKrentz

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Re: Brightness & Heat ratio difference between tungsten/halogen vs HMI?
« Reply #13 on: May 26, 2016, 06:07:08 pm »

I have another question regarding HMI.

How do I know when the bulb should be replaced?

The counter in my lamp is not working. I can see the colour change slightly and occasionally it might act up a little bit (goes off and goes on right away).

Should I wait for it to fail or it can be damaging to the equipment to do so?

If you feel something is wonky better replace it in time, you can still keep the lamp as "worst case" spare bulb. There is no secure sign for end of life (other than mechanical / broken glass etc) but usually you may have to deal with bad starting / turning off, bad color and lower light output, they will probably also have a thick white/grey coating inside the inner glass. All in all pretty much to deal with later in post which costs effort and money, too. Try to avoid switching the lamp off within the first minutes after start and let it reach its operating temperature first. The starting process is very erosive and shortens lamp life.

Cheers
Ulf

Edit: If the lamp is turning off while running fine and starts again right away, it might also be the security switch of the glass dome of course also the ballast may be faulty. Slightly color changes can be a sign for a bad ballast, too. Color changes within the first 5-10 minutes of operation is in specs, also color variation when dimming (light gets cooler when dimmed). Just replace the bulb first and see, what happens :-)
« Last Edit: May 26, 2016, 06:15:56 pm by UlfKrentz »
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