Anyone starting on the long and winding road of lighting might well be baffled at the number of very different approaches that he or she might find in books and articles. I certainly did, and that was probably because my training in Television had been engineering based, where the very nature of engineering provides specific answers to specific problems.
I think it is important to state that lighting is largely not like that. The difference between lighting and engineering is that when you are doing it for real, you can often break the rules. However, you can usually only break some of the rules some of the time!
I need to say that most of my career has been spent within the BBC which has devised and developed professional ways of working that are admired throughout the world of Broadcasting. It is only when on some of my early secondments abroad that I realised that all I took for granted in the Beeb was not to hand elsewhere.
Having said that, my approach to lighting is, perhaps, surprising in that although trained as an engineer, I am not a slave to Mireds, Lumens, or degrees Kelvin. Although I am aware of such technical things, I only measure the intensity of light with a meter when I know it will save me time and effort later. Having said that, my experience and preparation counts for much, and I know that by the time I get to a studio floor or a location, most of the important decisions will have been made by myself in advance. Once there and after focussing, I like to make my assessments of the absolute colour or brightness of a scene on a quality picture monitor.
OK, so a lighting cameraman (customary term, no sexist implication) will usually have to work to a ridiculously short time scale with no budget and only the lighting kit that he carries with him in the boot of his car. He/she will probably have to rely on the camera viewfinder for picture/lighting assessment. Having said that, I suggest that it would be a wise investment to start saving for a small, high quality colour monitor (such as can be seen elsewhere in this magazine) because it really will be your first important step to creating a better lit image.
I am familiar with the pressure when there’s no time for a recce; just rush, dash and compromise. Under those circumstances, it is hardly surprising that the end result is ‘illumination’ rather than ‘lighting’. What I hope to do in the scope of these articles is to give the reader the ability to come up with shots that are nicely balanced and lit in a believable and acceptable way.
Let’s just step back to the basics and a few techy facts. A typical modern camera sensitivity might be expressed as: F8.0 with illuminance of 2000 lux and 89.9% reflectance peak white with a 60db signal to noise ratio. This is an engineering specification and not to be taken as an indication of a working light level! I have been in studios where, unfortunately, this was literally taken as the case. But that’s another story.
However, 89.9% is a Japanese interpretation of peak white. After all, they tend to make the cameras and image ‘chips’. Most other countries use a 60% peak white, which is based on our need to expose Caucasian face tones without information being lost in any peak white areas. This translates as:
F8 with illuminance of 3000 lux and 60% reflectance peak white and 60db signal to noise ratio. However, engineers will only use cameras at F8 in the Lab. (we hope)
In the real world of television, we take advantage of those expensive bits of glass and metal at the front of the camera. Just by opening up the lens by two stops, the illumination requirement goes down from a toasting 3000 lux to a much more manageable 750 lux at F4. Even more manageable if we open another stop to F2.8 as that gives us less than 400 lux.
The working lens aperture (as opposed to the engineering spec) is principally determined from depth-of-field considerations. The incident light level used in any television studio depends on the light required by the cameras in use in that studio to give a similardepth of field to that found in other television studios. The thinking behind this was to give a consistency to images produced in BBC Studios throughout the UK.
In recent decades, operational practice has become more flexible as Lighting Directors and lighting cameramen exert more influence on picture quality than engineers. This is not to denigrate the engineer but really to reflect the huge improvements in television camera quality and stability that has occurred. Lighting people use differences in colour temperature to give their pictures character and style rather than seeing them as bad practice. The great thing about lighting is that it’s about ‘what you like’ and ‘what I like’. There are rules that we need to know, but then we can (selectively) break them if it produces shots that ‘you’ and ‘I’ like.
At this stage, let’s state the obvious. There are essentially two broad categories of lighting situations. Either you have total control of the lighting: i.e. a studio or ‘black box’ situation or you are working in an ambient or a mixed light situation. For the time being I would like to talk about the first situation where everything is under your control. I was trained and practised my lighting for many years in such well controlled situations; BBC Studios around the U.K.
A working range of light levels for most lit studios would be in the region of 200-600 lux. Cameras, lamps and lighting control equipment have all improved but there is an irrefutable law that governs the fall off of light intensity with respect to the inverse square of the distance of the source from the object to be illuminated. It is called the Inverse Square law and affects all lighting people everywhere. Ignore it at your peril!
If you double the distance from the light source to your meter, the intensity goes down to a quarter. That is definitely not in your favour! As you can see from the chart above, a light source of one candela emits one lumen into each square metre which equates to one lux. Manufacturers of lamps (properly called luminaires) will quote their light output in peak candelas. It’s then relatively easy to work out the light incidence at the ‘subject’. A colleague of mine has created a pretty exhaustive table for most of the TV lamps available to the European L.D/cameraman that will be featured in a future article.
So far, I have talked about an even field of light arriving at a flat, featureless surface and have measured its value as incident light in lux or foot-candles. If only the world were that simple! Foot candles tend to be regarded as a historic unit here in the U.K. although they are alive and well in the U.S.A. [One foot candle is equivalent to 11.1 lux.]
As well as intensity, light has colour. The human eye is remarkably adaptive to changes in the colour of what we call ‘white’ light. Outside in daylight, we accept sunlight as ‘white’ light. When it illuminates objects they appear coloured by virtue of the light absorbed or reflected from the object. When we go indoors into a room lit by electric light, (lets call it a studio) then we also quickly adjust our eye/brain to accept that tungsten light is also ‘white’. Our TV cameras, however, are not quite so clever.
We have all seen TV footage of someone being interviewed indoors, which has been very orange in appearance, and conversely, sometimes seen an outdoor shot, which is very blue. These are both examples in which the thinking part of a TV camera (the cameraman) has forgotten to change the colour temperature operating point from the previous shoot. Easily done I guess in a rushed situation and with no colour monitor reference.
A good way to visualise the ‘colour temperature’ of a light source is to visualise a bar of metal being gradually heated up in a blacksmiths forge. As the bar gets hotter, the colour of the bar will change from dull red, through orange, yellow, and white to pale blue if the forge is hot enough. Those temperatures can clearly be measured and do relate to the colour of the light which is produced.
Below is a simple chart, which illustrates the relationship between some typical light sources and their colour temperature measured in degrees Kelvin. The Kelvin scale begins at absolute zero which is –273 Celsius but its individual units are the same size as Celsius.
Choosing the colour temperature operating point
The two most important colour temperatures for lighting people are the ones encountered either in daylight which equates to around 5600K or in a ‘black box’ environment (Studio or windowless room) where tungsten filament luminaires are used at a colour temperature of around 3000K. Most cameras have the ability to change between daylight and tungsten lighting at the flick of a switch.
Cameras are designed to be at their most efficient when working in tungsten light (3000K) and it relatively easy to shape the response curves electronically for daylight working. This involves a loss in sensitivity, but this is not usually a problem in view of the normally much higher light levels of daylight.
Historically, cameras used to have an optical filter, which was known as a ‘minus blue’ (actually a CTO [colour temperature orange]) needed to prevent overload of the blue tube. Modern ‘chip’ cameras with their excellent highlight overload abilities can cope with the range of colour temperatures purely electronically. Life as a lighting person has actually got easier over the years!
In television studios the colour temperature of the light sources that illuminate people will usually be within 150 K of the ’line-up’ colour temperature i.e. 2850K +or-150K. That tolerance used to be quite strictly applied in the early days of colour television when drifting electronics were a major headache and engineers were very much in charge, but extension of these limits can be (and are) used as a creative tool by enterprising L.D.’s. Having said that, it is still a good idea to start with a studio line up light set at a known colour temperature and intensity lighting a line up chart when working in a multi camera situation.
On location, I would say that +or- 400K is an acceptable swing from the colour of ‘Daylight’ which is defined as 5600K. Similarly, an enterprising L.D. will use colour temperature variation between sources as part of his creative process when appropriate.
To summarise: we have chosen an operating point for the cameras based on the colour temperature of the ambient light. We are able to measure the quantity and assess the quality and colour of that light arriving at the subject and ensure that that is within the operating requirements of our camera(s). So does that mean that we’re ready to shoot? Well, not quite. It’s helpful to know about contrast ratios and handling of the camera and the scene itself and how lighting can help. That’s the scope of my next article which will also lead into portraiture lighting.