Forums > Photography Talk > Question about light bulb wattage

Photographer

Camerosity

Posts: 5317

Saint Louis, Missouri, US

Zack Zoll wrote:
Well, they kind of are.  Kind of.  Assuming that everyone rates everything the same way (they don't), a 25 w/s strobe should be the same exposure at any synced flash speed as a 25 watt bulb with a 1 second exposure at the same aperture and ISO.  Different manufacturers rate their lights more or less conservatively, but that's a ballpark figure.

So if everything is on the up-and-up, then a 1000 watt halogen shot at 1/60 should be as bright as a 16.7 w/s strobe.  Which is actually pretty crappy.  That means that if you were using umbrellas,(warning: head math) you'd probably need to be at something like 800 ISO if you wanted to shoot at f/5.6.

Yeah, I used to believe the same thing. I was taught that 100 watt-seconds was the same amount of light that’s produced by a 100-watt tungsten light bulb in one second. In other words, I was taught that a watt-second is a unit of light.

Then a couple of months ago a photographer who generally knows what he’s talking about contradicted that in a forum post that said the efficiency of the light source has to be factored in.

So I called Photogenic and talked to one of their engineers, who told me that a watt-second is indeed a unit of energy, not a unit of light – and that the efficiency of the light sources does have to be factored in.

In other words, 100 watt-seconds is NOT the same as 100 watts of tungsten light for one second. A 100 watt-second flash consumes the same amount of energy (in 1/1000 second or whatever the flash duration is) that a 100-watt bulb consumes in one second.

Since tungsten bulbs are inefficient light sources (more energy is consumed by producing heat than by producing light), a strobe at 100 watt-seconds produces much more than a 100-watt tungsten bulb produces in one second.

I even called Paul C. Buff Co. and got a second opinion from one of their engineers. She told me the same thing that the Photogenic engineer did.

Mar 25 13 03:56 pm Link

Photographer

Camerosity

Posts: 5317

Saint Louis, Missouri, US

ontherocks wrote:
i think the modeling light in a strobe would be better than that?

for my part i'd rather have a window than a constant light. although we do use fluorescents for shooting products. but fluorescents can get weirdly green in the shadows.

KevinMcGowanPhotography wrote:
I agree totally with both statements.    My strobes can have modeling lights of either 150watts or 250 watts.     And yes even "daylight" fluorescent lights are not not quite truly daylight. 

Lights that give a clean color temp are a LOT easier to deal with than those that are just close.

Yeah, and I'll bet your modeling lamps are tungsten halogen bulbs, not tungsten bulbs. Which means that your modeling lamps produce more light than regular tungsten bulbs of the same wattage.

Mar 25 13 03:59 pm Link

Photographer

Camerosity

Posts: 5317

Saint Louis, Missouri, US

Fred Gerhart wrote:
The modeling lamps in strobes do not accurately reflect the strobes power. They try but fail.

Depends on the strobes. Most "professional" strobes allow you to vary the power of the light to match the power setting of the strobe. So if I'm using two identical 1000 watt-second strobes, one set at 200 watt seconds and the other set at 100 watt-seconds, the modeling lamps will be proportional, and the one in the strobe powered at 200-watt seconds will be twice as bright as the other.

Mar 25 13 04:04 pm Link

Photographer

Zack Zoll

Posts: 2641

Glens Falls, New York, US

Post edited.  It was explained better while I was typing, and there the answer was when I was done smile

Mar 25 13 04:07 pm Link

Photographer

Camerosity

Posts: 5317

Saint Louis, Missouri, US

Fred Gerhart wrote:
The modeling lamps in strobes do not accurately reflect the strobes power. They try but fail.

KevinMcGowanPhotography wrote:
I think there are usually 2 issues with modeling lights in strobes.
1.  Is what you say, they are not as powerful as the strobes..
2.  And this is the bigger influence.  Most strobes have round flash tubes and
     the modeling light is a pinpoint light source so the strobe gives a broader light due to the flash tube's design.

Not sure what brand of strobes you’re using, Kevin. My Photogenic Solairs have flash tubes that are “hollowed” in the center at the back (the plug end) of the tubes. The long, narrow halogen modeling lamps fit in the hollowed-out part of the flash tube. So the flash tubes and the modeling lamps are centered in exactly the same spot. And since the modeling lamp is completely “surrounded by” the flash tube, except at the plug end, the size of the modeling lamp is effectively the size of the flash tube that surrounds it.


KevinMcGowanPhotography wrote:
I think that most people don't aim strobes properly. I find i get a LOT more control if I feather the light greatly.  I rarely ever point a light directly at the subject. Doing so usually over lights the scene.  Take that light, turn it 30 degrees or more off the subject, maybe more towards the camera then point it up at a white ceiling.  It still lights the subject but with bounce light.. and looks a lot more (TO ME) natural.

When I observe light in a room, it's rarely anything direct.  It's bouncing off of things outside the windows, then bounces off of walls, furniture, ceilings, inside the room.

I find taking that "non-direct" lighting philosophy helps my lighting look more subtle.  I can still get a pretty light on my subject, but with more subtle control.

Exactly. I almost always feather “direct” lights (those with no translucent fabric between the flash tube and the subject, like softboxes have). I find this to be especially effective with a beauty dish. It’s like the beauty dish can be two very different light sources, depending on whether it’s feathered or not. I often do the same thing with an Octobox with no translucent fabric.

Sometimes I even feather softboxes – especially strip boxes – for the same reason.

KevinMcGowanPhotography wrote:
Also I've moved to very low watt/second power settings.  I'm quite happy with settings under 50 w/s.  And that's adding modifiers like softboxes, umbrellas and scrims.

Yep. More often than not my 1000-watt second Solairs are powered down to somewhere in the 11-50 watt-second range. (Minimum power is 11.something watt-seconds.)

A thousand watt-seconds was nice when people shot Kodachome at ASA/ISO 10. It’s rarely necessary these days unless you’re lighting a stage or a basketball court.

Mar 25 13 04:16 pm Link

Photographer

WR Photographics

Posts: 1396

Regina, Saskatchewan, Canada

Try these. They seem really bright. I don't know what colour balance they are.

http://www.homedepot.ca/product/husky-5 … pod/826659

Mar 25 13 04:20 pm Link

Photographer

Michael Fryd

Posts: 3893

Miami Beach, Florida, US

natural beauties of qld wrote:

Not true.

Heat is infrared light and the proportion of infrared light emitted falls as the temperature of the emitting body rises.

The notion that all power ends up as heat is true only in the long run. As far as light is concerned, it is true only once all the visible light has been absorbed by bodies cool enough to re-radiate the energy solely as infrared (every body above absolute zero (i.e. zero degrees Kelvin, or -271 degrees centigrade) radiates infrared).

This is elementary physics.

No.  Heat is not infrared light.   "Heat" is informally defined to be the transfer of thermal energy by convection, radiation, or conduction.

Anything with a temperature above absolute zero will radiate energy.  The wavelength of that radiation is dependent on the temperature of the object.  Something at 100° F will radiate in the infrared range.  Something at about 3,000° K will radiate visible light at the same color temp as an incandescent light bulb.   Something at about 6,000° K will radiate daylight.

The notion that all power ends up as heat is true in the long run.  For many situations, it is also true (or an extremely good approximation) in the short run.

When it comes to lights, all the energy is converted to heat or light.  Assuming all the windows are closed, all the light is absorbed in the room.  Pretty much 100% of the energy gets converted to heat in the short term.  You move away from the short term when some of the energy is converted to kinetic energy.  For instance a fan that draws 100W of energy will turn some of it to heat, and some will go towards moving the air.  As the air bumps into walls and other objects, it will slow down, and convert that kinetic energy to heat.  Thus it may take a few minutes for all the energy to end up as heat.

The bottom line is that this really is very simple.  A 100W light bulb (LED, incandescent, or fluorescent) will put 100W of heat into the room.  This is the same as a 100W Easy-Bake oven, a 100W TV, or a 100W space heater.  In terms of heat load, there is no noticeable difference between any of these.  In terms of light output, a hundred Watts of power pumped into a LED light will likely give you about 5 times more light that a hundred Watts pumped into a traditional incandescent bulb.


If you don't believe me, please do a web search before replying.  Don't reply with what you think, reply with the results of your research.

Mar 25 13 08:06 pm Link

Photographer

Michael Fryd

Posts: 3893

Miami Beach, Florida, US

To put this into perspective:

Assuming you are shooting at 1/60th of a second, you need 260 standard 100W light bulbs in order to get the same exposure as a 160WS Alien Bee B400 monolight at full power.  (You would also need a source of over 200 Amps of 120VAC power).  Those 260 light bulbs would draw 26 KiloWatts of power and generate a 26KW heat load (about 90,000 BTU).  Enough to heat a small home.

If you want to shoot at 1/250 you would need over 1,000 standard 100W light bulbs (and over 800 Amps of 120VAC power).


If you are willing to use a slower shutter speed and shoot at 1/30 second, you only need 130 standard 100W light bulbs.


If you are shooting a sill life with a 1 second exposure, you only need 4.5 standard 100W light bulbs (One Home Depot Work light).


If you are willing to shoot at 1/30, and are willing to open up your aperture 3 stops, then we are down to a manageable 1,600 Watts of incandescent, or three 500W Home Depot work lights.

If you are willing to shoot at 1/30, are willing to open up your aperture 3 stops, and are willing to up your ISO four stops (from ISO 100 to ISO 1600) then we only need a single 100W light bulb.

If you can't afford slow shutter speeds, high ISO, or wider apertures, then you need a heck of a lot of incandescent power to match a 160WS alien Bee.

There is a reason that continuous lights are called "Hot Lights".

Mar 25 13 08:30 pm Link

Photographer

WMcK

Posts: 5286

Glasgow, Scotland, United Kingdom

WR Photographics wrote:
Try these. They seem really bright. I don't know what colour balance they are.

http://www.homedepot.ca/product/husky-5 … pod/826659

It looks as if it only about 20W (100W tungsten equivalent) and the light from these is normally very blue with a poor CRI.

Mar 26 13 01:28 pm Link

Photographer

Zack Zoll

Posts: 2641

Glens Falls, New York, US

Michael Fryd wrote:
No.  Heat is not infrared light.   "Heat" is informally defined to be the transfer of thermal energy by convection, radiation, or conduction.

...

The notion that all power ends up as heat is true in the long run.  For many situations, it is also true (or an extremely good approximation) in the short run.

...

The bottom line is that this really is very simple.  A 100W light bulb (LED, incandescent, or fluorescent) will put 100W of heat into the room.  This is the same as a 100W Easy-Bake oven, a 100W TV, or a 100W space heater.  In terms of heat load, there is no noticeable difference between any of these.  In terms of light output, a hundred Watts of power pumped into a LED light will likely give you about 5 times more light that a hundred Watts pumped into a traditional incandescent bulb.

I'm not sure what to think of all this.  You say some things that I know are true, and some others that I know are not.  And as a result, I honestly have a hard time believing you.

I pulled off the Easy Bake Oven comment because someone sort of explained it, but you're sort of going another way with it, so I'll bring it back.  Bear in mind that I'm neither a physics major nor a certified electrician - and while I'm not totally inept at wiring and handyman skills, I AM totally inept at physics.

You say that everything of equal wattage produces approximately equal heat.  The Easy Bake Oven comment was in reference to the fact that the bulb it uses (250 watts, as I recall) is about the same wattage as a tiny K-cup coffeemaker, despite the fact that the coffeemaker converts water to steam more-or-less instantly, and the E-B Oven is hardly efficient.  Granted the oven could have a power draw of less than 250 watts, but then why wouldn't it take a lower wattage bulb?  The oven is not producing heat directly, as the coffeemaker, so the idea that 'wattage on everything is equivalent' is already false.

Your average hair dryer is the same to twice the wattage of a large coffeemaker.  Not only will your hair dryer not boil/burn your hair in less than a minute, but would take hours to evaporate as much water as a coffeemaker does in minutes, even if you put the tip of the hair dryer IN the water.

Which you should never do.

Lastly, I have several amplifiers in my home.  One of them is a tube amplifier for a guitar, producing 15 watts.  The other is a solid state 5.1 amplifier producing 90 watts per channel, or 450 watts total, or 30 times as much as the guitar amp.  The power transformer for the guitar amp is only rated at 15 watts, so that's all the power that is even coming into the unit.

If I play guitar for a couple hours, the amp gets hot, and the room gets a few degrees warmer.  If I'm cleaning all day, I'll leave the 5.1 system playing music the whole time.  The temperature of the room remains exactly as the thermostat is set, despite having 30 times the wattage, and infinitely more air-to-surface friction from the much larger amount of speakers.  And that's not even factoring in the subwoofer, which sort of does its own thing.

So yeah, wattage does not equal heat, no Sir no how.  You're forgetting about voltage and amperage, and even maybe even impedance.  Granted, those things really don't matter so much with hot lights, as it is a more-or-less direct connection to your home or studio's wiring, and most of the watts spent are used for their intended purpose.  But all of those other things DO affect how things produce heat as a byproduct.  For instance, voltage regulators on an LED television can produce heat if the mains current in your house is higher than what the TV wants - that's part of why my guitar amp heats up.  That and the tubes, which have a similar function.  LED lights themselves produce very little heat, but the TV itself may be very warm, even if it only displaying a black picture, due to the regulators.  If the TV is displaying black then wattage isn't even an issue, since the bulbs aren't on, and are thus not outputting any watts.

Michael Fryd wrote:
If you don't believe me, please do a web search before replying.  Don't reply with what you think, reply with the results of your research.

Pot?  Kettle?

I may not be an expert in any of this stuff, but I've fried enough circuits to know when somebody else is oversimplifying.

Mar 26 13 05:11 pm Link

Photographer

Rob Photosby

Posts: 2995

Brisbane, Queensland, Australia

Zack Zoll wrote:

I'm not sure what to think of all this.  You say some things that I know are true, and some others that I know are not.  And as a result, I honestly have a hard time believing you.

I pulled off the Easy Bake Oven comment because someone sort of explained it, but you're sort of going another way with it, so I'll bring it back.  Bear in mind that I'm neither a physics major nor a certified electrician - and while I'm not totally inept at wiring and handyman skills, I AM totally inept at physics.

You say that everything of equal wattage produces approximately equal heat.  The Easy Bake Oven comment was in reference to the fact that the bulb it uses (250 watts, as I recall) is about the same wattage as a tiny K-cup coffeemaker, despite the fact that the coffeemaker converts water to steam more-or-less instantly, and the E-B Oven is hardly efficient.  Granted the oven could have a power draw of less than 250 watts, but then why wouldn't it take a lower wattage bulb?  The oven is not producing heat directly, as the coffeemaker, so the idea that 'wattage on everything is equivalent' is already false.

Your average hair dryer is the same to twice the wattage of a large coffeemaker.  Not only will your hair dryer not boil/burn your hair in less than a minute, but would take hours to evaporate as much water as a coffeemaker does in minutes, even if you put the tip of the hair dryer IN the water.

Which you should never do.

Lastly, I have several amplifiers in my home.  One of them is a tube amplifier for a guitar, producing 15 watts.  The other is a solid state 5.1 amplifier producing 90 watts per channel, or 450 watts total, or 30 times as much as the guitar amp.  The power transformer for the guitar amp is only rated at 15 watts, so that's all the power that is even coming into the unit.

If I play guitar for a couple hours, the amp gets hot, and the room gets a few degrees warmer.  If I'm cleaning all day, I'll leave the 5.1 system playing music the whole time.  The temperature of the room remains exactly as the thermostat is set, despite having 30 times the wattage, and infinitely more air-to-surface friction from the much larger amount of speakers.  And that's not even factoring in the subwoofer, which sort of does its own thing.

So yeah, wattage does not equal heat, no Sir no how.  You're forgetting about voltage and amperage, and even maybe even impedance.  Granted, those things really don't matter so much with hot lights, as it is a more-or-less direct connection to your home or studio's wiring, and most of the watts spent are used for their intended purpose.  But all of those other things DO affect how things produce heat as a byproduct.  For instance, voltage regulators on an LED television can produce heat if the mains current in your house is higher than what the TV wants - that's part of why my guitar amp heats up.  That and the tubes, which have a similar function.  LED lights themselves produce very little heat, but the TV itself may be very warm, even if it only displaying a black picture, due to the regulators.  If the TV is displaying black then wattage isn't even an issue, since the bulbs aren't on, and are thus not outputting any watts.


Pot?  Kettle?

I may not be an expert in any of this stuff, but I've fried enough circuits to know when somebody else is oversimplifying.

You are correct in your comment that "wattage does not equal heat" (at least in the short run, and the short run is what we are interested in.)

It is important to understand that wattage is a measure of the energy that the device will consume and is not a direct measure of its output, when output is defined as useful output - e.g. kinetic energy with an electric motor, visible light with strobes/studio lights, heat from an oven, etc. (With your amplifiers, it is also a measure of the maximum energy that the device will consume.  Unless you run them flat out, they will consume less than the maximum power.)

The underlying issue here is efficiency, i.e. how much useful output is produced for a given amount of input. With lights, the useful output is visible light.

An ordinary incandescent bulb is comparatively inefficient in term of producing visible light. It relies on a heated element glowing in a glass envelope filled with inert gas (to stop the filament from vaporising).  A large part of the light that it gives off is infrared light that is invisible to the eye, but which we can feel as heat coming off the bulb.

If the temperature at which the filament glows is increased, the proportion of light given off as visible light increases, and that is why halogens are more efficient than traditional incandescent lamps.

Fluorescent tubes operate by exciting a gas which emits ultraviolet light, which, in turn, excites a coating inside the tube and causes it to emit visible light.  Importantly, it does so with greater efficiency than lamps that rely on heating a filament.

In the context of this thread, comparisons between lights and heaters are a bit pointless because the useful output from a heater is heat whereas heat is the undesirable output from lights.

Mar 26 13 06:59 pm Link

Mar 26 13 08:23 pm Link

Photographer

Michael Fryd

Posts: 3893

Miami Beach, Florida, US

Zack Zoll wrote:

Michael Fryd wrote:
No.  Heat is not infrared light.   "Heat" is informally defined to be the transfer of thermal energy by convection, radiation, or conduction.

...

The notion that all power ends up as heat is true in the long run.  For many situations, it is also true (or an extremely good approximation) in the short run.

...

The bottom line is that this really is very simple.  A 100W light bulb (LED, incandescent, or fluorescent) will put 100W of heat into the room.  This is the same as a 100W Easy-Bake oven, a 100W TV, or a 100W space heater.  In terms of heat load, there is no noticeable difference between any of these.  In terms of light output, a hundred Watts of power pumped into a LED light will likely give you about 5 times more light that a hundred Watts pumped into a traditional incandescent bulb.

I'm not sure what to think of all this.  You say some things that I know are true, and some others that I know are not.  And as a result, I honestly have a hard time believing you.

I pulled off the Easy Bake Oven comment because someone sort of explained it, but you're sort of going another way with it, so I'll bring it back.  Bear in mind that I'm neither a physics major nor a certified electrician - and while I'm not totally inept at wiring and handyman skills, I AM totally inept at physics.

You say that everything of equal wattage produces approximately equal heat.  The Easy Bake Oven comment was in reference to the fact that the bulb it uses (250 watts, as I recall) is about the same wattage as a tiny K-cup coffeemaker, despite the fact that the coffeemaker converts water to steam more-or-less instantly, and the E-B Oven is hardly efficient.  Granted the oven could have a power draw of less than 250 watts, but then why wouldn't it take a lower wattage bulb?  The oven is not producing heat directly, as the coffeemaker, so the idea that 'wattage on everything is equivalent' is already false.

Your average hair dryer is the same to twice the wattage of a large coffeemaker.  Not only will your hair dryer not boil/burn your hair in less than a minute, but would take hours to evaporate as much water as a coffeemaker does in minutes, even if you put the tip of the hair dryer IN the water.

Which you should never do.

Lastly, I have several amplifiers in my home.  One of them is a tube amplifier for a guitar, producing 15 watts.  The other is a solid state 5.1 amplifier producing 90 watts per channel, or 450 watts total, or 30 times as much as the guitar amp.  The power transformer for the guitar amp is only rated at 15 watts, so that's all the power that is even coming into the unit.

If I play guitar for a couple hours, the amp gets hot, and the room gets a few degrees warmer.  If I'm cleaning all day, I'll leave the 5.1 system playing music the whole time.  The temperature of the room remains exactly as the thermostat is set, despite having 30 times the wattage, and infinitely more air-to-surface friction from the much larger amount of speakers.  And that's not even factoring in the subwoofer, which sort of does its own thing.

So yeah, wattage does not equal heat, no Sir no how.  You're forgetting about voltage and amperage, and even maybe even impedance.  Granted, those things really don't matter so much with hot lights, as it is a more-or-less direct connection to your home or studio's wiring, and most of the watts spent are used for their intended purpose.  But all of those other things DO affect how things produce heat as a byproduct.  For instance, voltage regulators on an LED television can produce heat if the mains current in your house is higher than what the TV wants - that's part of why my guitar amp heats up.  That and the tubes, which have a similar function.  LED lights themselves produce very little heat, but the TV itself may be very warm, even if it only displaying a black picture, due to the regulators.  If the TV is displaying black then wattage isn't even an issue, since the bulbs aren't on, and are thus not outputting any watts.


Pot?  Kettle?

I may not be an expert in any of this stuff, but I've fried enough circuits to know when somebody else is oversimplifying.

A 250W easy bake oven generates the same heat as a 250W light bulb or a 250W heating element.

The difference is the distribution of the heat.  Three 100W lightbulbs produce the same total heat whether they are in different parts of the room, or in the same spot.  If they are in the same spot, that spot will get very hot.  If they are in different parts of the room, you will have three, not-as-hot spots.


Many appliances with draw varying amounts of power as they operate.  For instance a refrigerator draws more power when the compressor is operating and the light is on.  These devices are rated at their maximum draw, not their average or typical draw.

Light bulbs are simple devices.  A 100W light bulb has a constant draw of 100W  None of the power goes to motors, fans, or gets stored in springs.  All of the power of the light bulb gets converted to heat or light.  That light bounces around the room, until it gets absorbed by various objects and heats that object.  This absorption happens very quickly.  Turn the light off and all the light gets absorbed in will under a second.

So yes,  With a light bulb, all of the energy goes to heating the room.


If you have a complicated object like a guitar amp, the power consumption varies with volume.  If you measure the actual power used (in Watts), all of this turns to heat.  Some goes directly to heat, the rest to sound.  Sound gets absorbed by the walls and turns to heat.

This is all elementary physics 

One of the most fundamental principles of physics is the Conservation of Energy. According this principle, energy can not be created or destroyed but may be transformed from one form to another.  A lightbulb converts a portion of the input power directly to heat, and a portion to light.  The light turns to heat as it is absorbed by various surfaces.  This a light bulb converts 100% of the input power to heat.


You really don't have to believe me. 

[url=http://www.newton.dep.anl.gov/askasci/eng99/eng99475.htm]Argonne National Laboratory's Educational Program[url=http://www.cns.cornell.edu/cipt/la … ed to heat

http://www.air-n-water.com/heater_volt.htm

http://www.solartanic.com/index_022.htm

Mar 26 13 09:12 pm Link

Photographer

NothingIsRealButTheGirl

Posts: 33590

Los Angeles, California, US

Even if they aren't the same brightness, I think the one thing you can probably say is a 250W bulb of one kind and a 250W bulb of another kind will make the same sized ding in your wallet when the electric bill comes due.

Mar 26 13 09:18 pm Link