During 2016-2017 I blogged about the production of Above the Clouds, a comedy road movie which I shot for director Leon Chambers. It premiered at Raindance in 2018, closely followed by Austin Film Festival, where it won the audience award for Best Narrative Feature, the first of four gongs it would collect.
In two decades of filmmaking, Above the Clouds is easily in the top five productions I’m most proud of. Since this January it has been available on Amazon, iTunes, Google Play and other platforms, and I highly recommend you give it a watch. DO NOT continue reading this blog unless you have, because what follows are two blog entries that I held back due to spoilers.
The script calls for Charlie to be seen sitting in the window seat of a plane as it rises quite literally above the clouds. This is another micro-set filmed in Leon’s living room, in fact half in the living room and half in the hall, to leave enough room for the lights beyond.
Although the view out of the window will be added in post, I need to simulate the lighting effect of bursting through the clouds. My plan involves a 1.2K HMI, and a 4×4 poly board held horizontally with a triple layer of 4×4 Opal sheets hanging from one edge.
We start with the HMI pointed straight into the window and the poly board held high up so that the Opal hangs in front of the lamp. As the plane supposedly rises through the cloud layer, Colin lowers the poly until it is below the level of the lamp, while Gary tilts the HMI down so its light skips off the poly (like sun skipping off the top of clouds) and bounces back up into the window. Gary then tilts the HMI back up to point straight into the window, to suggest further banking or climbing of the aircraft. This direct light is so hot that it bounces off the armrest of Charlie’s seat and gives a glow to her cheek which syncs perfectly with a smile she’s doing.
Today’s set is a dark room. A photographer’s dark room, that is. Not just a random dimly-lit room.
We begin with only the red safe-light in play. The wall-mounted practical has a 15W bulb, so it needs some serious help to illuminate the room. Micky rigs a 1K pup with Medium Red gel and fires it over the top of the set, above the practical. The effect is very convincing. Pure red light can make everything look out of focus on camera, which is why I chose the slightly magenta Medium Red gel, rather than the more realistic Primary Red. The colourist will be able to add some green/yellow to correct this.
During the scene, Naomi pulls a cord and the normal lights come on. These are two hanging practicals, fitted with dimmed 100W tungsten globes. In a very similar set-up to yesterday, we use a 2K with a chimera, poking over the set wall on the camera’s down-side, to enhance and soften the practicals’ light.
To read all the Above the Clouds blogs from the start, click here.
A simple enough slug line, and fairly common, but amongst the most challenging for a cinematographer. In this article I’ll break down into five manageable steps my process of lighting woodlands at night.
1. Set up the moon.
Forests typically have no artificial illumination, except perhaps practical torches carried by the cast. This means that the DP will primarily be simulating moonlight.
Your “moon” should usually be the largest HMI that your production can afford, as high up and far away as you can get it. (If your production can’t afford an HMI, I would advise against attempting night exteriors in a forest.) Ideally this would be a 12K or 18K on a cherry-picker, but in low-budget land you’re more likely to be dealing with a 2.5K on a triple wind-up stand.
Why is height important? Firstly, it’s more realistic. Real moonlight rarely comes from 15ft off the ground! Secondly, it’s hard to keep the lamp out of shot when you’re shooting towards it. A stand might seem quite tall when you’re right next to it, but as soon as you put it far away, it comes into shot quite easily. If you can use the terrain to give your HMI extra height, or acquire scaffolding or some other means of safely raising your light up, you’ll save yourself a lot of headaches.
The size of the HMI is of course going to determine how large an area you can light to a sufficient exposure to record a noise-free image. Using a good low-light camera is going to help you out here. I shot a couple of recent forest night scenes on a Blackmagic Pocket Cinema Camera, which has dual native ISOs, the higher being 3200. Combined with a Speedbooster, this camera required only 1 or 2 foot-candles of illuminance, meaning that our 2.5K HMI could be a good 150 feet away from the action. (See also: “How Big a Light do I Need?”)
2. Plan for the reverse.
A fake moon looks great as a backlight, but what happens when it comes time to shoot the reverse? Often the schedule is too tight to move the HMI all the way around to the other side, particularly if it’s rigged up high, so you may need to embrace it as frontlight.
Frontlight is generally flat and undesirable, but it can be interesting when it’s broken up with shadows, and that’s exactly what the trees of a forest will do. Sometimes the pattern of light and dark is so strong and camouflaging that it can be hard to pick out your subject until they move. One day I intend to try this effect in a horror film as a way of concealing a monster.
One thing to look out for with frontlight is unwanted shadows, i.e. those of the camera and boom. Again, the higher up your HMI is, the less of an issue this will be.
If you can afford it, a second HMI set up in the opposite direction is an ideal way to maintain backlight; just pan one off and strike up the other. I’ve known directors to complain that this breaks continuity, but arguably it does the opposite. Frontlight and backlight look very different, especially when smoke is involved (and I’ll come to that in a minute). Isn’t it smoother to intercut two backlit shots than a backlit one and frontlit one? Ultimately it’s a matter of opinion.
3. Consider Ground lights.
One thing I’ve been experimenting with lately is ground lights. For this you need a forest that has at least a little undulation in its terrain. You set up lights directly on the ground, pointed towards camera but hidden from it behind mounds or ridges in the deep background.
I once tried this with an HMI and it just looked weird, like there was a rave going on in the next field, but with soft lights it is much more effective. Try fluorescent tubes, long LED panels or even rows of festoon lights. When smoke catches them they create a beautiful glow in the background. Use a warm colour to suggest urban lighting in the distance, or leave it cold and it will pass unquestioned as ambience.
Put your cast in front of this ground glow and you will get some lovely silhouettes. Very effective silhouettes can also be captured in front of smoky shafts of hard light from your “moon”.
4. Fill in the faces.
All of the above looks great, but sooner or later the director is going to want to see the actors’ faces. Such is the cross a DP must bear.
On one recent project I relied on practical torches – sometimes bounced back to the cast with silver reflectors – or a soft LED ball on a boom pole, following the cast around.
Big-budget movies often rig some kind of soft toplight over the entire area they’re shooting in, but this requires a lot of prep time and money, and I expect it’s quite vulnerable to wind.
A recipe that I use a lot for all kinds of night exteriors is a hard backlight and a soft sidelight, both from the same side of camera. You don’t question where the sidelight is coming from when it’s from the same general direction as the “moon” backlight. In a forest you just have to be careful not to end up with very hot, bright trees near the sidelight, so have flags and nets at the ready.
5. Don’t forget the Smoke.
Finally, as I’ve already hinted, smoke is very important for a cinematic forest scene. The best options are a gas-powered smoke gun called an Artem or a “Tube of Death”. This latter is a plastic tube connected to a fan and an electric smoke machine. The fan forces smoke into the tube and out of little holes along its length, creating an even spread of smoke.
All smoke is highly suspectible to changes in the wind. An Artem is easier to pick up and move around when the wind changes, and it doesn’t require a power supply, but you will lose time waiting for it to heat up and for the smoke and gas canisters to be changed. Whichever one you pick though, the smoke will add a tremendous amount of depth and texture to the image.
Overall, nighttime forest work scenes may be challenging, but they offer some of the greatest opportunities for moody and creative lighting. Just don’t forget your thermals and your waterproofs!
Many light sources we come across today have a CRI rating. Most of us realise that the higher the number, the better the quality of light, but is it really that simple? What exactly is Colour Rendering Index, how is it measured and can we trust it as cinematographers? Let’s find out.
What is C.R.I.?
CRI was created in 1965 by the CIE – Commission Internationale de l’Eclairage – the same body responsible for the colour-space diagram we met in my post about How Colour Works. The CIE wanted to define a standard method of measuring and rating the colour-rendering properties of light sources, particularly those which don’t emit a full spectrum of light, like fluorescent tubes which were becoming popular in the sixties. The aim was to meet the needs of architects deciding what kind of lighting to install in factories, supermarkets and the like, with little or no thought given to cinematography.
As we saw in How Colour Works, colour is caused by the absorption of certain wavelengths of light by a surface, and the reflection of others. For this to work properly, the light shining on the surface in the first place needs to consist of all the visible wavelengths. The graphs below shows that daylight indeed consists of a full spectrum, as does incandescent lighting (e.g. tungsten), although its skew to the red end means that white-balancing is necessary to restore the correct proportions of colours to a photographed image. (See my article on Understanding Colour Temperature.)
Fluorescent and LED sources, however, have huge peaks and troughs in their spectral output, with some wavelengths missing completely. If the wavelengths aren’t there to begin with, they can’t reflect off the subject, so the colour of the subject will look wrong.
Analysing the spectrum of a light source to produce graphs like this required expensive equipment, so the CIE devised a simpler method of determining CRI, based on how the source reflected off a set of eight colour patches. These patches were murky pastel shades taken from the Munsell colour wheel (see my Colour Schemes post for more on colour wheels). In 2004, six more-saturated patches were added.
The maths which is used to arrive at a CRI value goes right over my head, but the testing process boils down to this:
Illuminate a patch with daylight (if the source being tested has a correlated colour temperature of 5,000K or above) or incandescent light (if below 5,000K).
Compare the colour of the patch to a colour-space CIE diagram and note the coordinates of the corresponding colour on the diagram.
Now illuminate the patch with the source being tested.
Compare the new colour of the patch to the CIE diagram and note the coordinates of the corresponding colour.
Calculate the distance between the two coordinates, i.e. the difference in colour under the two light sources.
Repeat with the remaining patches and calculate the average difference.
Here are a few CRI ratings gleaned from around the web:
LitePanels 1×1 LED
Problems with C.R.I.
There have been many criticisms of the CRI system. One is that the use of mean averaging results in a lamp with mediocre performance across all the patches scoring the same CRI as a lamp that does terrible rendering of one colour but good rendering of all the others.
Further criticisms relate to the colour patches themselves. The eight standard patches are low in saturation, making them easier to render accurately than bright colours. An unscrupulous manufacturer could design their lamp to render the test colours well without worrying about the rest of the spectrum.
In practice this all means that CRI ratings sometimes don’t correspond to the evidence of your own eyes. For example, I’d wager that an HMI with a quoted CRI in the low nineties is going to render more natural skin-tones than an LED panel with the same rating.
I prefer to assess the quality of a light source by eye rather than relying on any quoted CRI value. Holding my hand up in front of an LED fixture, I can quickly tell whether the skin tones looks right or not. Unfortunately even this system is flawed.
The fundamental issue is the trichromatic nature of our eyes and of cameras: both work out what colour things are based on sensory input of only red, green and blue. As an analogy, imagine a wall with a number of cracks in it. Imagine that you can only inspect it through an opaque barrier with three slits in it. Through those three slits, the wall may look completely unblemished. The cracks are there, but since they’re not aligned with the slits, you’re not aware of them. And the “slits” of the human eye are not in the same place as the slits of a camera’s sensor, i.e. the respective sensitivities of our long, medium and short cones do not quite match the red, green and blue dyes in the Bayer filters of cameras. Under continuous-spectrum lighting (“smooth wall”) this doesn’t matter, but with non-continuous-spectrum sources (“cracked wall”) it can lead to something looking right to the eye but not on camera, or vice-versa.
Given its age and its intended use, it’s not surprising that CRI is a pretty poor indicator of light quality for a modern DP or gaffer. Various alternative systems exist, including GAI (Gamut Area Index) and TLCI (Television Lighting Consistency Index), the latter similar to CRI but introducing a camera into the process rather than relying solely on human observation. The Academy of Motion Picture Arts and Sciences recently invented a system, Spectral Similarity Index (SSI), which involves measuring the source itself with a spectrometer, rather than reflected light. At the time of writing, however, we are still stuck with CRI as the dominant quantitative measure.
So what is the solution? Test, test, test. Take your chosen camera and lens system and shoot some footage with the fixtures in question. For the moment at least, that is the only way to really know what kind of light you’re getting.
If you’ve ever read or been taught about lighting, you’ve probably heard of the Inverse Square Law. It states that light fades in proportion to the square of the distance from the source. But lately I started to wonder if this really applies in all situations. Join me as I attempt to get to the bottom of this…
But before we go into that, let’s get the Law straight in our minds. What, precisely, does it say? Another excellent book, Gerald Millerson’s Lighting for Television and Film, defines it thusly:
With increased distance, the light emitted from a given point source will fall rapidly, as it spreads over a progressively larger area. This fall-off in light level is inversely proportional to the distance square, i.e. 1/d². Thus, doubling the lamp distance would reduce the light to ¼.
The operative word, for our purposes, is “spreads”.
If you’d asked me a couple of years ago what causes the Inverse Square Law, I probably would have mumbled something about light naturally losing energy as it travels. But that is hogwash of the highest order. Assuming the light doesn’t strike any objects to absorb it, there is nothing to reduce its energy. (Air does scatter – and presumably absorb – a very small amount of light, hence atmospheric haze, but this amount will never be significant on the scale a cinematographer deals with.)
In fact, as the Millerson quote above makes clear, the Inverse Square Law is a result of how light spreads out from its source. It’s purely geometry. In this diagram you can see how fewer and fewer rays strike the ‘A’ square as it gets further and further away from the source ‘S’:
Each light ray (dodgy term, I know, but sufficient for our purposes) retains the same level of energy, and there are the same number of them overall, it’s just that there are fewer of them passing through any given area.
So far, so good.
Taking the Law into my own hands
During season two of my YouTube series Lighting I Like, I discussed Dedo’s Panibeam 70 HMI. This fixture produces collimated light, light of which all the waves are travelling in parallel. It occurred to me that this must prevent them spreading out, and therefore render the Inverse Square Law void.
This in turn got me thinking about more common fixtures – par cans, for example.
Par lamps are so named for the Parabolic Aluminised Reflectors they contain. These collect the light radiated from the rear and sides of the filament and reflect it as parallel rays. So to my mind, although light radiated from the very front of the filament must still spread and obey the Inverse Square Law, that which bounces off the reflector should theoretically never diminish. You can imagine that the ‘A’ square in our first diagram would have the same number of light rays passing through it every time if they are travelling in parallel.
Similarly, fresnel lenses are designed to divert the spreading light waves into a parallel pattern:
Even simple open-face fixtures have a reflector which can be moved back and forth using the flood/spot control, affecting both the spread and the intensity of the light. Hopefully by now you can see why these two things are related. More spread = more divergence of light rays = more fall-off. Less spread = less divergence of light rays = more throw.
So, I wondered, am I right? Do these focused sources disobey the Inverse Square Law?
Breaking the law
To find the answer, I waded through a number of fora.
Firstly, and crucially, everyone agrees that the Law describes light radiated from a point source, so any source which isn’t infinitely small will technically not be governed by the Law. In practice, says the general consensus, the results predicted by the Law hold true for most sources, unless they are quite large or very close to the subject.
If you are using a softbox, a Kinoflo or a trace frame at short range though, the Inverse Square Law will not apply.
The above photometric data for a Filmgear LED Flo-box indeed shows a slower fall-off than the Law predicts. (Based on the 1m intensity, the Law predicts the 2m and 3m intensities as 970÷2²=243 lux and 970÷3²=108 lux respectively.)
A Flickr forum contributor called Severin Sadjina puts it like this:
In general, the light will fall off as 1/d² if the size of the light source is negligible compared to the distance d to the light source. If, on the other hand, the light source is significantly larger than the distance d to the light source, the light will fall off as 1/d – in other words: slower than the Inverse Square Law predicts.
Another contributor, Ftir, claims that a large source will start to follow the Law above distances equal to about five times the largest side of the source, so a 4ft Kinoflo would obey the Law very closely after about 20ft. This claim is confirmed by Wikipedia, citing A. Ryer’s The Light Measurement Handbook.
But what about those pesky parallel light beams from the pars and fresnels?
Every forum had a lot of disagreement on this. Most people agree that parallel light rays don’t really exist in real life. They will always diverge or converge, slightly, and therefore the Law applies. However, many claim that it doesn’t apply in quite the same way.
A fresnel, according to John E. Clark on Cinematography.com, can still be treated as a point source, but that point source is actually located somewhere behind the lamp-head! It’s a virtual point source. (Light radiating from a distant point source has approximately parallel rays with consequently negligible fall-off, e.g. sunlight.) So if this virtual source is 10m behind the fixture, then moving the lamp from 1m from the subject to 2m is not doubling the distance (and therefore not quartering the intensity). In fact it is multiplying the distance by 1.09 (12÷11=1.09), so the light would only drop to 84% of its former intensity (1÷1.09²=0.84).
I tried to confirm this using the Arri Photometrics App, but the data it gives for Arri’s fresnel fixtures conforms perfectly with an ordinary point source under the Law, leaving me somewhat confused. However, I did find some data for LED fresnels that broke the Law, for example the Lumi Studio 300:
As you can see, at full flood (bottom graphic) the Law is obeyed as expected; the 8m intensity of 2,500 lux is a quarter of the 4m intensity of 10,000 lux. But when spotted (top graphic) it falls off more rapidly. Again, very confusing, as I was expecting it to fall off less rapidly if the rays are diverging but close to parallel.
A more rapid fall-off suggests a virtual point source somewhere in front of the lamp-head. This was mentioned in several places on the fora as well. The light is converging, so the intensity increases as you move further from the fixture, reaching a maximum at the focal point, then diverging again from that point as per the Inverse Square Law. In fact, reverse-engineering the above data using the Law tells me – if my maths is correct – that the focal point is 1.93m in front of the fixture. Or, to put it another way, spotting this fixture is equivalent to moving it almost 2m closer to the subject. However, this doesn’t seem to tally with the beam spread data in the above graphics. More confusion!
I decided to look up ETC’s Source Four photometrics, since these units contain an ellipsoidal reflector which should focus the light (and therefore create a virtual point source) in front of themselves. However, the data shows no deviation from the Law and no evidence of a virtual point source displaced from the actual source.
I fought the law and the law won
I fear this investigation has left me more confused than when I started! Clearly there are factors at work here beyond what I’ve considered.
However, I’ve learnt that the Inverse Square Law is a useful means of estimating light fall-off for most lighting fixtures – even those that really seem like they should act differently! If you double the distance from lamp to subject, you’re usually going to quarter the intensity, or near as damn it. And that rule of thumb is all we cinematographers need 99% of the time. If in doubt, refer to photometrics data like that linked above.
And if anyone out there can shed any light (haha) on the confusion, I’d be very happy to hear from you!
The latest episode of Lighting I Like is out, analysing how the “Splinter Chamber” set is lit in time travel thriller 12 Monkeys. This adaptation of the Terry Gilliam movie can be seen on Netflix in the UK.
The first step in lighting a daytime interior scene is almost always to blast a light through the window. Sometimes soft light is the right choice for this, but unless you’re on a big production you simply may not have the huge units and generators necessary to bounce light and still have a reasonable amount of it coming through the window. So in low budget land, hard light is usually the way we have to go.
Now, I used to think that this hard window light had to hit the talent’s faces, otherwise what’s the point? But eventually I learnt that there are many things you can do with this light….
1. Light the talent directly.
This is what I always used to do. The problem is that the light will be very harsh. If there is a good amount of natural light coming in through the window too, that might soften the look enough. If not, slipping a diffusion frame in front of the light will take the edge off the hardness. And it depends which way the talent is facing. If the hard light is backlighting or edging them, the effect might well be beautiful.
2. Light part of the talent directly.
This is a nice way to get the best of both worlds. You hit their clothes with the hard light, maybe a bit of their chin too; it creates contrast, brings out the texture in the costume, and adds dynamics because as the talent moves, the edge of the hard light will move around on them. To light the parts which the hard source doesn’t hit you can use bounce, or a kinoflo Window Wrap.
3. Light the floor.
Arrange the light so it hits the floor, creating a skip bounce. Unless the floor’s a very dark colour, the light will bounce back up and light your talent softly from below. While some people are afraid of the “monster” look of lighting from below, it can often produce a very beautiful look. It’s well worth exploring. Alternatively, bounce the hard window light off a wall to create a soft side light.
4. Light the background.
A hot splash of “sunlight” on the background is a common way to add interest to a wide shot. It can show off the production design and the textures in it, or help frame the talent or separate them from the background.
5. Light nothing.
Sometimes the most effective way to use a shaft of light through a window is simply as background interest. Volumize the light using smoke, and it creates a nice bit of contrast and production value in the scene. Silhouetting characters in front of the beam can be very effective too.
Any that I’ve missed? What are your techniques for lighting through windows?
Following on from last week’s look at tungsten units, today we focus on HMI lighting. HMIs are more complex technology than tungsten, meaning they are far more expensive, and more prone to problems, particularly if you get a deal from a hire company and they give you older units. But they are bright and relatively efficient and because of this, and their colour temperature of 5,600K, they are by far the most popular type of light used in today’s film and TV industry when battling or mixing with natural daylight.
HMIs (hydragyrum medium-arc iodide) operate by creating an arc between two electrodes. This arc excites a gas which produces the light. In order to ignite the arc, a ballast is required. This device also regulates the current, while a special header cable connects the ballast to the light.
Ballasts come in two types: electronic and magnetic. Magnetic ballasts are cheaper, but if you are shooting at a shutter interval out of sync with the cycling of your power supply – e.g. 1/48th of a second with a 50Hz UK power supply – the HMI will appear to flicker on camera. Electronic ballasts have a ‘flicker free mode’ which converts the sine wave of the power supply into a square wave so that the arc does not extinguish at any point in the cycle. A side effect of this is that the head and/or ballast can produce humming, buzzing or squealing noises. Therefore many electronic ballasts have a ‘silent mode’ which reduces the noise but only prevents flicker at standard frame rates, not for high-speed work. In practice, flicker is rarely a problem as the shutter angles of today’s digital cameras can easily be tweaked to deal with it at common frame rates.
Like tungsten units, HMIs are available in open face, par and fresnel varieties, though the open face models are not very common. Arri, the major manufacturers of HMIs, call their daylight par fixtures ‘Arrisun’. Other HMI brands include Film Gear, Silver Bullet and K5600, which makes Jokers (see below).
Measured by their wattage, standard HMIs sizes are: 200W, 575W, 1.2K, 2.5K, 4K, 6K, 12K, 18K.
The smaller models, up to 2.5K, are fairly common on no-budget sets, because they can run off a domestic power supply and so don’t require a generator. At the other end of the scale, 18Ks are standard for daylight exterior and interior work on medium budgets and above.
Because of their power, HMIs often play a key part in night exterior lighting too. A 12K or 18K on a condor crane may be used to simulate the moon, while other HMI units, perhaps bounced or coming through a frame, might serve as sidelight or fill. By choosing to shoot at 3,200K, you automatically turn these HMI sources blue, often a desirable look for nighttime work.
There are many variants on the standard HMIs. Here are some of the more common ones.
Pocket pars are little 125W daylight pars that can be run off batteries. Before the days of LED panels, I used one of these for eye-light on a short film set in a forest in daylight. They can also make a good TV gag when bounced off a wobbling silver reflector.
Jokers are small units that come in 400W and 800W models. They can be reconfigured in various ways and even slotted into Source 4 housings (see last week’s tungsten post) to convert these units to daylight. We used a 400W joker a couple of times on Heretiks, when there was little space to rig in but we needed a fair bit of punch – like daylight through a small window.
The Arrimax range uses a hybrid of par and fresnel technology. They are lighter and more efficient than standard HMIs – the 800W model puts out almost as much light as an ordinary 1.2K, for example – but they’re more expensive to hire and don’t create the nice shafts of light that some DPs like (ahem). The model numbers are the wattage in tenths of a kilowatt: M8 (800W), M18 (1.8K), M40 (4K), M90 (9K) and the anomalously-named Arrimax 18/12 which accepts both 12K and 18K bubbles.
Helium Balloons are designed to provide a soft overhead illumination for night exteriors or high-ceilinged interiors. They come in a range of shapes and sizes, and aren’t necessarily HMIs; they can be fitted with tungsten lamps, or a combination of both.
Again, please let me know on Facebook or Twitter if I’ve missed out any of your favourite units. Next week: fluorescents.
Welcome to the first in a series of posts looking at the many types of lighting instruments in use on film and TV sets today. This is not intended to be an exhaustive or comprehensive list, but it will give you a good idea of your options, particularly if you’re moving up from smaller productions – where lighting kit is mostly borrowed – to larger ones, where you’re required to submit a lighting list to a rental house.
Some of the key considerations when choosing a lamp are:
Incandescent lamps work by passing electrical current through a wire filament which becomes so hot that it glows. In the film industry they are generally referred to as ‘tungsten‘ units after the metal which the filament is made from. Common tungsten lamps include Dedolites, 1K ‘babies’ and open-face 800W and 2KW units (which have misogynous nicknames I shall not repeat here).
Pros: cheap, dimmable, extremely high CRI
Cons: very inefficient, get very hot, colour temperature changes when dimmed
Colour temperature: 3,200K
Light quality: generally hard (although certain units like Space Lights are softer)
The HMI (hydragyrum medium-arc iodide) is the most common form of high intensity discharge lamp used in the industry. It operates by creating an electrical arc between two electrodes which excites a gas. You may occasionally hear about an MSR (medium source rare-earth), which is slightly different technology, but as far as a cinematographer is concerned MSRs and HMIs are the same. They require a ballast to ignite the arc and regulate the current and voltage.
Pros: good CRI, good match for daylight, efficient
Cons: only dimmable down to 50%, expensive, heads and ballasts sometimes hum or ‘squeal’, older bulbs can vary in colour, flicker issues at certain shutter angles with magnetic ballasts
Fluorescent lamps are found almost everywhere today, as strip lights in supermarkets and offices, and energy-saver bulbs in the home. Similar in principle to HMIs, electric current causes mercury vapour to emit UV light which is translated into the visible spectrum by the phosphor coating on the tube. Kino Flo pretty much has the monopoly on fluorescent lighting for the film industry. Like HMIs, fluorescents require a ballast.
Pros: reasonable CRI from Kino Flos (appalling CRI from domestic/commercial fixtures), very efficient, get warm but not hot
Cons: limited dimming, high fall-off of light
Colour temperature: 5,500K and 3,200K tubes available
Gradually replacing tungsten as the most common lamps found on no-budget shoots, LED (light emitting diode) units contain semi-conductors that emit light when their electrons reconfigure. The technology is advancing rapidly, but there is currently a wide range of LED lamps on the market, varying greatly in price and corresponding quality.
Pros: extremely efficient, barely get warm, can run off batteries, almost fully dimmable, some models have adjustable colour temperature
Cons: CRI ranges from almost acceptable in the expensive models to downright shocking in the cheaper ones
Colour temperature: varies
Light quality: varies
Though there are other types of lighting, like xenon, metal-halide and HEP (high efficiency plasma), the above four are the main ones you will encounter on film and TV sets today. Over the next few weeks I’ll look at each of those types in more detail, listing many of the specific units available in each category and their applications.