Strobe (Flash) vs. Halogen continuous lighting - quantified and compared

[Curtis N]

The local chapter of the Measurbator's Anonymous called a special meeting to determine quantitative answers to a few questions regarding continuous vs. strobe lighting in recent threads, namely this thread (http://photography-on-the.net/forum/showthread.php?t=205528)by FlyingPete and this thread (http://photography-on-the.net/forum/showthread.php?t=203521) by shedsomelight.

We decided to compare the AlienBees B800 (http://alienbees.com/b800.html)studio flash unit, a popular, reasonably priced and relatively low powered studio strobe, with a pair of 500 watt halogen shop lights such as you might find in hardware stores and home centers.

The AlienBees unit was not actually tested. Comparisons below are based on the advertised guide number specifications of the unit.

Output from the halogen shop light (two 500 watt lights on a stand, 1000 watts total) was measured by aiming them squarely at a pair of 18% gray cards at a measured distance of 10 feet and metering the cards with a camera.

Truth be told, you can poke all kinds of holes in my methodology and question the technical accuracy of my conclusions. But the data will be profound enough to make its point, even if the numbers are a bit off.

Ok, here are the numbers:

The AlienBees unit has a guide number of 172 feet with the standard reflector. So let's round that down a bit and say that theoretically it will meter at around f/16 at a distance of 10 feet.

The gray cards illuminated by the halogen fixture metered at 1/25 second (0.04 seconds) and f/4 at the same distance.

If you wanted to use the same aperture and ISO with both units, you would need a shutter speed of about 0.64 seconds with the halogens to get the same exposure as the strobe.

0.64 seconds of 1000 watts equals 640 watt-seconds. This is reasonably close to the AlienBees' advertised rating of 800 effective watt-seconds, accounting for probable differences in reflectors and angles of coverage.

If you wanted to use a 1/200 shutter speed and the same aperture and ISO with both units, you would theoretically need 128,000 watts of halogen lights to match the output of the strobe.

Another interesting comparison: Using the sunny 16 rule as a guide, it would theoretically take 64,000 watts of halogen light at a distance of 10 feet to equal the brightness of a sunny day.

[FlashZebra]

Curtis,

I suggest you call this work.

"Why electronic flash is so popular. Or, why 128,000 Watts can't be wrong"

Interesting compairison, thank you.

Enjoy! Lon

[Wilt]

So, a conclusion one can derive is: one strobe (in your test) is equal to two suns!

Another conclusion: One strobe can run off one household 20A circuit, but you would need 6400 housecircuits to run the same amount of halogen lights!

Did you compute the amount of air conditioning (how many BTU total capacity) to negate the effects of all those halogen lights? That would take some more household circuits to support, too!

This is neato!

[Curtis N]

So, a conclusion one can derive is: one strobe (in your test) is equal to two suns!At 1/200 shutter speed and 10 feet, yes. But it's only equal to one sun at a distance of 14 feet. The actual duration of the flash is only 1/3200 second, so while it's actually on, the flash is equal to 32 suns at 10 feet.Did you compute the amount of air conditioning (how many BTU total capacity) to negate the effects of all those halogen lights?1 watt equals 3.412 btu/hr, and all of the light that doesn't escape through a window is going to ultimately be absorbed by some surface and converted to heat. So 128,000 watts of lights would require a 437,000 btu air conditioner to maintain the room temperature.

A side note: when I was standing next to (not even in front of) the halogen fixture to take a reading, the heat was enough to make me break a sweat!

[Wilt]

At 1/200 shutter speed and 10 feet, yes. But it's only equal to one sun at a distance of 14 feet. The actual duration of the flash is only 1/3200 second, so while it's actually on, the flash is equal to 32 suns at 10 feet.1 watt equals 3.412 btu/hr, and all of the light that doesn't escape through a window is going to ultimately be absorbed by some surface and converted to heat. So 128,000 watts of lights would require a 437,000 btu air conditioner to maintain the room temperature.

A side note: when I was standing next to (not even in front of) the halogen fixture to take a reading, the heat was enough to make me break a sweat!

So it would not be good enough to buy softboxes that are designed for hot lights, if you used all the halogens...no room for all of the softboxes and also the room would melt (let alone the softboxes!)

[FlashZebra]

At 1/200 shutter speed and 10 feet, yes. But it's only equal to one sun at a distance of 14 feet. The actual duration of the flash is only 1/3200 second, so while it's actually on, the flash is equal to 32 suns at 10 feet.1 watt equals 3.412 btu/hr, and all of the light that doesn't escape through a window is going to ultimately be absorbed by some surface and converted to heat. So 128,000 watts of lights would require a 437,000 btu air conditioner to maintain the room temperature.

A side note: when I was standing next to (not even in front of) the halogen fixture to take a reading, the heat was enough to make me break a sweat!
With the incandescent lights, the part of the energy that is actually converted to light is rather trivial.

Standing in front of two 500 Watt lights is just about like standing in front of a garden-variety hair dryer. I think the hair dryers are only slightly higher Wattage (more like 1200 or 1300 Watts).

At a former location for our camera club, on a few particularly cold evenings we often turned on a couple of 1000 Watt photo lights to help warm up the place. They put out more heat that the very common 1500 Watt electrical space heaters.

You cannot use these units and escape the fact that a Watt is a unit specifically geared toward energy (actually energy per unit time) and not a measurement of light intensity.

A 500 Watt incandescent light could be accurately described as a 500 Watt heater that just incidentally puts off some light as a byproduct.

Enjoy! Lon

[FlashZebra]

So, a conclusion one can derive is: one strobe (in your test) is equal to two suns!
I like this "sun" unit a lot.

Humans can relate to the intrinsic amount of light produced by the sunlight on earth.

So, how about rating flash units in "sun" units (of course a fixed distance would need to be established). Three meters (very close to 10 feet) has some appeal. This distance might also be at or near the typical flash to subject distance for photographs of human beings.

It would also make outside flash use relate to the competition, the sun. And might even help humans internalize lighting ratio use outside.

Possibly we can get the ball rolling on this "sun" unit.

Enjoy! Lon

[Wilt]

Lon, we may have a whole new ad campaign to counter the Alien Bee and White Lightning 'equivalent watt-second'? We should go peddle the idea to other manufacturers of lighting of all types, that they use our idea (for a fee, of course) to advertise the output in 'sun equivalent' units! I get dibs on 'Western U.S.' (west of Mississippi_; rest of the world is open for grabs.

One flaw, though, is that the sun is less intense up near the Arctic (Northern Canada, Scandinavia, Finland, etc.) and down near Tierra del Fuego.

[FlashZebra]

... the sun is less intense up near the Arctic and down near Tierra del Fuego.
I am also less intense in Tierra del Fuego..

Always liked the sound of that name Tierra del Fuego.

Enjoy! Lon

[GageYoung]

This was helpful! Thank you.

[PhotoJourno]

Thanks, Curtis-Man, this is pretty good data, to help sustain what many had assumed. I have both (strobes and Halogens), and for me the Heat issue is alone, a huge problem.

Strobe seems to be a generation above, with modeling light and the right guide number. Thank goodness I won't have to make this test myself now.

I do keep the Halogens for big events, hallways, and other such. They do eliminate quite a bit.

Thanks again, sir.

[PacAce]

Wilt and Lon, while you guys are working out your marketing strategy for selling the sun unit idea, I'm going to go try out my two hair blowers to see if I can use them reliably for lighting. I'll need to make me a sync cable to hook them up to my camera first, though, unless you, Lon, just happen to have one that I can borrow for a couple of hours.

Curtis, interesting findings you posted although some of the number, at first look, don't seem to add up. But I just ate and don't want to get indigestion so I'm not going to delve into the math thing right now.

;) :)

[Wilt]

Leo, the sun unit marketing has died its death. I am now trying to convince TMR Design to offer the SoupSphere (wonton take-out container turned into a flash diffuser, so we can get exhorbitant sums of money and charge $9 return fees, undercutting our buddy Fong)

[FlashZebra]

Leo, the sun unit marketing has died its death. I am now trying to convince TMR Design to offer the SoupSphere (wonton take-out container turned into a flash diffuser, so we can get exhorbitant sums of money and charge $9 return fees, undercutting our buddy Fong)
I am glad you are finally speaking up Wilt.

I have been frantically working on the both the mechanics of the "sun unit", and the associated marketing campaign. Wilt has evidently been staying close to home learning to play the harmonica.

Most of this "sun unit" work is being done in my converted cold fusion laboratory under the bleachers at Stagg Field at the University of Chicago.

Current plans call for a massive roll out at the Super Bowl, with Michael Bolton and grand niece of "Mr. Wizard" as spokespersons.

Wilt, I am glad that you have opted out, as that leaves all that gravy just for me.

With all the cash I will be scooping up I think I will buy myself a new 3 pack of underwear (briefs), a slurpie, and a one of those purple things that rotate.

Enjoy! Lon

[Curtis N]

Leo,
Here's the math, in a nutshell.
1/25 shutter (0.04 seconds) at f/4 is equivalent to 0.64 seconds at f/16.
(I suppose I could have metered it at f/16 to make it easier, but let's just pretend I did.)
1/200 shutter is 0.005 seconds.
0.64 divided by 0.005 = 128.
So you would need 128 times as much light as my 1000w halogen to get the light equivalent of the AB with a 1/200 shutter speed.
(That's 128,000 watts I think, but I did that part in my head.)

[FlashZebra]

Leo,
Here's the math, in a nutshell.
1/25 shutter (0.04 seconds) at f/4 is equivalent to 0.64 seconds at f/16.
(I suppose I could have metered it at f/16 to make it easier, but let's just pretend I did.)
1/200 shutter is 0.005 seconds.
0.64 divided by 0.005 = 128.
So you would need 128 times as much light as my 1000w halogen to get the light equivalent of the AB with a 1/200 shutter speed.
(That's 128,000 watts I think, but I did that part in my head.)
A couple of questions since it seems you can cipher:

1) How close are you to Stagg field?

2) Do you already know how to play the harmonica? I have already lost one partner to that instrument.

Enjoy! Lon

[Curtis N]

1) About 80 miles, according to mapquest.
2) I can make sound come out of it, but I don't think I'd be able to call it music.

[Lotto]

Thanks for the measurements, Curts.

Anyone want to take shot at this question? If a magnify glass is placed in front the Alien Bees and focus to the background paper, how many pops of Bees is needed to burn a hole through the paper? :)

[Wilt]

Thanks for the measurements, Curts.

Anyone want to take shot at this question? If a magnify glass is placed in front the Alien Bees and focus to the background paper, how many pops of Bees is needed to burn a hole through the paper? :)

Infinite number of pops...while the magnifying glass concentrates the light, it is for such a brief period of time as to have the heat dissipated within the paper simply by the mass of the paper conducting energy away from the target spot. Additionally, due to the 1 second recycle time of the flash, convection further carries heat energy away from the paper to the air molecules which are surrounding the paper. The AB needs to recycle infinitely faster for this to work!

[Chris]

One of the problems with the halogens as I discovered in my office with one of those homemade light boxes is that if you let your wired trigger get too close to the halogen light it will melt. Doh!!

[PacAce]

Thanks for the measurements, Curts.

Anyone want to take shot at this question? If a magnify glass is placed in front the Alien Bees and focus to the background paper, how many pops of Bees is needed to burn a hole through the paper? :)

Infinite number of pops...while the magnifying glass concentrates the light, it is for such a brief period of time as to have the heat dissipated within the paper simply by the mass of the paper conducting energy away from the target spot. Additionally, due to the 1 second recycle time of the flash, convection further carries heat energy away from the paper to the air molecules which are surrounding the paper. The AB needs to recycle infinitely faster for this to work!
You're wrong, Wilt. According to Curtis, the AB is equivalent to 32 suns that 10 feet. So, all you need to do see how long it takes to burn a hold in the bg paper with the sun and then divide that time by 32 and pop the AB continously for that amount of time (assuming the bg is 10 feet from the AB). :lol:

[Curtis N]

Is the paper white or black? That would make a huge difference.

Back when I was young and stupid (2 years ago), I tried using strips of vinyl electrical tape on the front of a flash unit to reduce its output. It only took one pop to make the tape start to smoke. The flash was behind the subject as a background light, so the rising smoke provided a cool effect.

... and of course that flash unit will never be the same.

[Wilt]

You're wrong, Wilt. According to Curtis, the AB is equivalent to 32 suns that 10 feet. So, all you need to do see how long it takes to burn a hold in the bg paper with the sun and then divide that time by 32 and pop the AB continously for that amount of time (assuming the bg is 10 feet from the AB). :lol:


But the sun shines constantly. The AB flashes at 1/400 sec. at most. The intensity might match, but the duration does not. So the laws of thermodynamics prevent the AB from catching anything on fire, due to conduction and convection of energy!

[PacAce]

But the sun shines constantly. The AB flashes at 1/400 sec. at most. The intensity might match, but the duration does not. So the laws of thermodynamics prevent the AB from catching anything on fire, due to conduction and convection of energy!

Yeah, you're right but I was thinking you could lower the power to increase the flash duration, move the strobe closer to the background to get the intensity back up again and then fire the strobe continuously. :confused:

And if that doesn't work, just touch the strobe tube against the background, set it to full power and then put a match head between them. That should get the background burning very fast, no? :lol:

[In2Photos]

Yeah, you're right but I was thinking you could lower the power to increase the flash duration, move the strobe closer to the background to get the intensity back up again and then fire the strobe continuously. :confused:

And if that doesn't work, just touch the strobe tube against the background, set it to full power and then put a match head between them. That should get the background burning very fast, no? :lol:
You should try it Leo and report back. I am interested but sadly I have no strobes. :( :lol:

[Lotto]

Dang, if we keep going with this, the halogen light will definitely have an advantage.

[photojournalista]

Why are we looking at watts when we should be comparing lumens (light output)?

[PacAce]

Why are we looking at watts when we should be comparing lumens (light output)?

'Cuz it's more fun working with watts and watts of lights. ;) :)

[Curtis N]

Why are we looking at watts when we should be comparing lumens (light output)?The question of "Should I buy strobes or continuous lights?" gets asked about once a week. The purpose of this thread was to compare the two in terms that a novice can understand and relate to.

[FlashZebra]

Why are we looking at watts when we should be comparing lumens (light output)?
Well, I do not think Watts were actually being compared.

In his very nice comparison, Curtis came to a bottom line of how many Watts of power would be needed using incandescent bulbs, for a particular amount of time, to net the same exposure as a reasonable flash exposure.

At no time were the Wattage of the incandescent lights compared to any Wattage consumption of the flash gear.

So underlying this comparison is the accomplishment of a particular exposure using two methods. The two exposure methods are actually compared, not a direct comparison of the Wattage used by the two methods.

The declared Wattage of the incandescent side of the comparison is just that, a declaration of an accessible and understandable attribute of that aspect of the methodologies being compared (accomplishing equal exposures).

As an important side note, for this comparison exposure time is also a fundamental aspect. An aspect that a direct lumen comparison would overlook. It is not just the intensity of the light, but the net effect of a particular intensity gathered over a period of time.

What needs to be compared is exposure, and that was accomplished, and Curtis did this in a very playful yet still accurate manner.

Enjoy! Lon

[In2Photos]

'Cuz it's more fun working with watts and watts of lights. ;) :)
ROFLMAO! That was great Leo. Thanks.

[bwolford]

The AlienBees unit has a guide number of 172 feet with the standard reflector. So let's round that down a bit and say that theoretically it will meter at around f/16 at a distance of 10 feet.

Can you measurebate this a little more for me? I don't understand the math.

I used 2 500 watt work lights when I started.

I measurebator tests show that if you put 30 girls in gymnastics leotards and pose them in such a way that the same 2 x 500 watt work lights illuminate them evenly, all 30 girls will complain of the heat from the lights in a 15,000 square foot gymnasium. ;) I didn't try the same experiment in different gymnasiums, but I did take a similar shot with 1 x AB800 in the same gymnasium and the only complaint I got was how long it took us to get them posed so that each would be properly illuminated. :rolleyes:

Interesting side note, putting an AB800 with the standard reflector at the top of a AB 10ft light stand on a floor exercise apparatus next to a ladder perched at a similar height is not a good idea.

[Curtis N]

The standard guide number formula: GN = f number * distance
or f number = GN/distance

172/10 = 17.2
So theoretically it will meter at f/17.2 at 10 feet.

I rounded it down to f/16 to make the math easier.

[subtle_spectre]

Watt is going here? Watt is this post aboutSomebody please il-lumen-ate me!:lol::lol:

[bwolford]

Thanks Curtis. Still haven't memorized your stickies yet. I appreciate that.

[SuperHuman21]

Excellent thread.

Just to make sure that I'm correct in my thinking, if the B800 does 14,000 Ls, then isn't that the same as a 14,000 lumens continuous light being on for one second? If that's the case then it just further confirms the jaw-dropping numbers Curtis has brought up.

I am mostly curious because I am looking into either buying the B400 or B800 for my jewelry/diamond/gems shooting. I think I have gathered that the B400 may be much more than enough because it's rated at 7,000 Ls and each light of mine is about 6200 lumens, with 2 of them (total of about 13,000 or so lumens) lighting the subject and one on the background.

Can someone confirm that a B400 may be more than enough? Sorry if it seems obvious but my brain isn't working lately as I have a really bad case of some dizziness and hardly can do anything for now, so I just read stuff up here :)

Thanks!

[snyderman]

The conclusions are probably sound. I didn't see "1.21 Jigawatts" anywhere in his whitepaper.

dave

[Titus213]

Excellent thread.

Just to make sure that I'm correct in my thinking, if the B800 does 14,000 Ls, then isn't that the same as a 14,000 lumens continuous light being on for one second? If that's the case then it just further confirms the jaw-dropping numbers Curtis has brought up.

I am mostly curious because I am looking into either buying the B400 or B800 for my jewelry/diamond/gems shooting. I think I have gathered that the B400 may be much more than enough because it's rated at 7,000 Ls and each light of mine is about 6200 lumens, with 2 of them (total of about 13,000 or so lumens) lighting the subject and one on the background.

Can someone confirm that a B400 may be more than enough? Sorry if it seems obvious but my brain isn't working lately as I have a really bad case of some dizziness and hardly can do anything for now, so I just read stuff up here :)

Thanks!

I think your dizziness may very well be caused by reading this thread. :lol:

I think a B400 should be more than adequate for shooting jewelry except for the directional issues caused by one light. You may have one of the few places where hot lights will work really well. Unless you are getting complaints.

[SuperHuman21]

I think your dizziness may very well be caused by reading this thread. :lol:

I think a B400 should be more than adequate for shooting jewelry except for the directional issues caused by one light. You may have one of the few places where hot lights will work really well. Unless you are getting complaints.

lol. I actually think that I got down this stuff pretty well, just trying to plug in the data for my own needs.

Yeah but I hate cont. lights 3 reasons, although just the heat is enough reason to switch:

1. Heat, regardless if that's fluorescent or actual hot lights (any lighting at these watts will heat you up). So, I get uncomfortable, the lights have to be very close to the objects and everything gets warped (like my paper reflectors and plexi).

2. Too bright. I get blinded too easily and when I put on sunglasses, I find that I often have to take them off to see where I'm focusing better.

3. Color balance is a huge pain since I'm doing JPEG and using cheap ("white balanced") fluorescents. The CRI is only like 83. I have to constantly update my color balance with a card because in this kind of shooting, everything's noticeable =/

Also, as a side note, for some odd and abrupt reason, my D90 on my older tripod, all of the sudden recently doesn't seem to stay sharp anymore under 1/125.

My only worry is the learning curve with knowing how the images will turn out once I actually shoot it. I know there's a modeling light but we'll see how it'll work for the diamonds and gems.

Oh yeah, and I was thinking of using a reflector since I'd be using one strobe for now, until I get the second one.

Thanks Titus!

[Titus213]

Get a meter too...

[SuperHuman21]

Lol. Everything costs money! I really don't want to get a meter but I suppose I should. You think it'll really help a lot in these shots? I only planned on spending like $400 but I see that'll be bumped up to like $600. Ha. It's an investment though :)

Thanks!