Light Sources for Still and Moving Images

Last updated: 11 January 2010
Published in: Digitising analogue media | Creating new digital media
Tags: digitisation | hardware | lighting | photography | supports and stands | tripod

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Summary

The word photography means drawing with light, without light it is impossible to record a video or still image. So lighting whether in a classroom, office or dedicated photographic studio is an essential component in a photograph or video. The captured image is a record of the light that is emitted, reflected or absorbed by the subject. With a basic understanding of light and how it can be modified the photographer or filmmaker should be able to improve the appearance of their images. This document will look at commonly used light sources and how the user can get the most from them.

Introduction

Light is electromagnetic radiation with a wavelength that is within the visible limits of the human eye. While ultra violet (UV) and infrared (IR) light can be detected by digital sensors and measured by light meters it is beyond normal human perception. Most sensors in digital cameras have IR cut filters mounted on them and some photographers use UV filters in front of the lens to reduce the influence of these non visible (to the human eye) frequencies on the final image. Infra red light can also confuse camera auto focussing systems as it is focussed differently to visible light.

An important quality of visible light is its colour temperature. White light is an equal mix of all of the different visible wavelengths however this combination is often unequal which produces a colour bias. This is known as its colour temperature and is measured in degrees kelvin (K),

Table of common light types and their colour temperatures in degrees Kelvin (K)

White balance controls in digital stills and video cameras are used to identify and correct for the colour bias of different light types.

To create an image whether still or moving a subject has to be illuminated, this could be by; daylight, artificial light such as a domestic household bulb, classroom lighting or specialist photographic lighting such as flash.

The commonly used unit of measure for the intensity of light (not flash) incident on a surface  is lux (lx)

A table of light levels (lux) for common situations

Still and video cameras are designed to deliver good quality results under typical light levels from between 500 lux to over 32000 lux. Under very dark or extremely bright conditions care must be taken to capture useable quality images.

Light Sources

Colour film used for still and moving images is designed to deliver high quality images under specific colour temperatures normally for daylight/flash or tungsten light.  For accurate colour under atypical lighting the analogue photographer or filmmaker normally has to attach colour correction (CC) film or gels over the lights or a CC filter over the lens. Digital stills and video cameras in contrast allow the user to correct for different light types ‘in camera’; this is known as white balancing. Generally speaking this now means that digital photographers and filmmakers are now free to work with most light types without the need for CC filters provided a few steps are taken.

We can divide light sources into two groups, ambient and artificial photographic lighting.

• Ambient is the light present in the scene before the photographer or filmmaker starts work.
• Artificial photographic lighting is light that the photographer or filmmaker introduces to the scene. Ambient and artificial light types can be used separately or combined with care.

Ambient light

Ambient light could be sunlight, moonlight, classroom lighting or domestic lighting etc. As it is the ‘native’ lighting in a scene it will normally give an atmospheric or believable look to an image. If, however, light levels are low, long exposures (using a tripod) or high ISO settings may be required which can prove challenging.

Daylight is the light we are most familiar with and we often try to replicate when we use artificial photographic sources such as flash. Daylight can also be unpredictable and doesn’t always produce the most pleasing illumination but with a little care the photographer or filmmaker can modify and improve the lighting by changing the camera angle, using shade, diffusers or reflectors. Bright sunshine can produce harsh shadows with high contrast, while clouds ‘soften’ the shadows and remove the three-dimensional look.

The colour temperature of daylight can also change; clouds absorb the ‘warmer’ red wavelengths of light which can give the subject a ‘cool’ bluish look. The colour of the light also changes slightly throughout the day; mornings and evenings normally have a ‘warm’ hue while the middle of the day is ‘cooler’. The cameras white balance settings are designed to produce neutral colour under a variety of light sources however, some professional photographers use the white balance settings creatively to inject some colour and mood into their photographs. The Raw file format (stills only) allows the user to experiment with different white balance settings in the knowledge that they can always re-apply the correct setting afterwards. The white balance settings cannot be changed in images captured in other formats.

Ambient Light- The Sun

Artificial ambient lighting is more consistent than daylight, though it lacks the intensity of bright sunshine. In typical offices and classrooms the lighting has been arranged to illuminate the specific work being undertaken. The lighting in a lecture theatre is normally directed towards the front of the room while a classroom or laboratory will have a more general illumination. In these types of locations photographic lighting such as flash or film lighting will distract both the lecturer and students and so the photographer or filmmaker will probably have to use the available ambient lighting. Before the photographer or filmmaker starts capturing images they should try to identify the dominant light source in the environment, its brightness levels and if possible its colour temperature or type eg. tungsten. Colour temperature may be difficult to identify; currently most classrooms and offices use fluorescent lighting; however a lecture theatre may have a combination of fluorescent, dimmable tungsten lights and possibly the light of a projector. While the camera can auto white balance for the dominant light source the weaker sources will probably still contribute to the lighting in the scene and may introduce a local colour cast.

Camera shake is a common problem when photographing under low light levels this can be prevented by increasing the ISO or using a stable support. There is more information on camera supports in the JISC Digital Media document Stands and Supports for Still and Moving Images. While it should be possible to capture good quality images without disturbing the subjects it is essential that consent is sought before shooting in a classroom or lecture theatre.

Typical lighting in a lecture theatre

In environments where lighting is used to illuminate large public areas over long periods of time the priority is energy efficiency and visibility rather than accurate colour rendition. Street lights in the UK for example normally have a strong yellow bias which is very hard to correct for. While it may be hard or even impossible to remove the yellow cast, it is atmospheric and represents how the scene appears. If the photographer wants to capture the true colour of the subject they will either have to light the subject with artificial photographic lighting or wait for daylight to return.

Available street lighting

Artificial photographic lighting

Artificial photographic lighting is the light that the photographer or filmmaker has introduced to a scene to augment or replace ambient lighting. In most film or stills studios high power tungsten, fluorescent or flash lights are the most widely used artificial lighting systems though it is also quite common to find domestic lights such as a desk lamp or a torch employed to illuminate parts of a subject. Artificial photographic lighting is a stable light source with a known colour temperature; its brightness can be controlled either directly via a switch or dial or by moving it closer to, or further from the subject. With ambient lighting the photographer or filmmaker has to make the most of what is in the scene, however they can choose which type of artificial light to use based on the lights suitability for the task.

Flash

Flash is the standard artificial light source used in still photography and is built in to the majority of digital cameras. Bare flash bulbs are small light sources and produce very direct lighting unless modified (see small light sources below). Both flash and daylight have roughly the same colour temperature and so they can be used together without creating white balance problems. Flash is often used with bright sunshine to lighten up or ‘fill in’ dark shadows. Although flashes produce a lot of light and some heat it is rapidly dissipated and should not harm the average subject. The brief duration of a flash (can be measured in thousandths of a second) makes it highly effective at recording moving objects. However this also makes it impossible to preview the lighting before the image is taken. To ensure a correctly captured picture the flash has to be triggered at the moment that the shutter is completely open, this is achieved via a flash synchronisation circuit which links the flash to the camera. Detachable flashes connect to this circuit via electrical contacts on the camera’s flash mount or ‘hot shoe’, remote flashes can be synchronised via a synch cable, triggered by other flashes (slave flash), infra red or radio signals. Most cameras will have a maximum shutter speed for flash synchronisation, slower speeds will all synchronise correctly, exceeding the flash sync speed will result in incorrectly exposed images.

The small pop up flashes built into cameras are very effective for ‘fill in’ flash but their proximity to the camera’s lens can result in ‘red-eye’.

Pop-up camera flash

Red eye

When bright light enters the eye it illuminates the tissue behind the retina which glows red. This red reflection then shines back out of the eye towards the camera, the result is known as red eye. If ambient light levels are increased then the pupil in the eye will contract, reducing the amount of light entering and therefore reflecting back out of the eye. Some cameras offer a red eye reduction feature were the camera emits a rapid burst of pre-flashes, in response the pupil reduces in size just before the picture is taken. Red eye can also be avoided by switching the flash off and using available light or if possible ‘bouncing’ the flash or using it ‘off camera’.

Detachable flashguns offer greater flexibility; they can be pointed directly at the subject, reflected or ‘bounced’ off a nearby wall or ceiling or removed from the camera and operated remotely. Modern detachable flashguns can exchange information with the camera before and during the exposure to improve focusing and exposure.

 
Left, camera ‘hot shoe’ top middle of frame. Right, detachable flash mounted on camera’s hot shoe

Studio flash systems offer considerably more power than camera-mounted systems but they are also less portable. Studio flashlights are normally fitted with a tungsten modelling light which simulates the flashlight; this assists the photographer in focussing and composing the image. Modelling lights do however radiate a lot of heat and they should be used with care when photographing sensitive objects.

  
Left, studio flash ‘head’. Right, wireless (radio) flash synchronisation

Tungsten or incandescent lighting

Tungsten or incandescent lighting is used by both photographers and filmmakers. Tungsten lights have a warm coloured light with a colour temperature of around 3500K and therefore should not be mixed with bright daylight or flash unless tungsten to daylight colour correction (CC) gels are placed over the lights. The bare tungsten filament is a small light source and produces a very direct light unless it is modified (see small light sources below). Most professional tungsten lights are fitted with black adjustable flaps or ‘barn doors’ which can be opened, closed or rotated to control the area of illumination, they can also be closed over the light to protect the bulb when not in use.

These lights draw a lot of power and normally need to be connected to a 240V supply and are therefore not suited to location photography. For location work, film units with large Hollywood budgets use mobile generators to power their lights however small scale video projects normally have to make do with reflectors or small camera mounted ‘top lights’ to provide ‘fill’.

Tungsten lights are highly inefficient and produce a lot of heat and infrared light. Human subjects soon start to feel uncomfortable under the light and the radiant heat can damage delicate objects.  The light’s casing can get quite warm but some parts of the light close to the bulb such as the adjustable barn doors can get extremely hot and should only be adjusted when cold or with thick leather gloves. To avoid the risk of fire, flammable materials shouldn’t ever be attached to the light or placed close to it. For safety reasons these lights should never be left unattended.

Domestic tungsten sources such as adjustable desk lights can be used to illuminate small areas and are a low cost, though less bright alternative to specialist tungsten lighting.

Tungsten studio light with barn doors attached

Fluorescent studio lights

Fluorescent studio lights are popular alternatives to tungsten for both stills and video photography. They produce a continuous light with colour temperatures ranging from 3200K to 5600K. These lights are far more efficient than tungsten lights and produce very little heat, which makes them suited to lighting delicate objects. At present however fluorescent bulbs do not produce the same amount of light as a single studio tungsten bulb. To increase the brightness, fluorescent lights often incorporate an array of bulbs; these may be switch able to alter the light output (most fluorescents cannot be fitted with dimmers). With larger bulbs grouped together in a single head fluorescents generally produce a ‘soft’ illumination we associate with large light sources (see large light sources below).

Some fluorescents, particularly those used at home and in offices do not offer a full spectrum and may lead to inaccurate colour so it would be wise to run some simple colour tests before using these lights photographically.

Normal AC mains electricity alternates at 50 cycles per second (50 hz), this can create a rapid shift in brightness with many types of light, particularly fluorescents. If a number of frames are taken of the same subject a shift in colour or tone may be seen as different frames are captured at different points in the flicker cycle. Manufacturers are beginning to resolve this, though it would be wise to run tests to check for flicker. If there is a noticeable shift, reduce the shutter speed (and compensate by closing the aperture) then check the results.

Fluorescent studio light

LEDs

LEDs (Light Emitting Diodes) are generating a lot of interest particularly in video making where there is a demand for a portable, energy efficient daylight balanced lighting system. LEDs produce full colour spectrum light with a colour temperature of 5500K. Like fluorescents, these systems use an array of tiny LEDs to create a large bright light source. The more LEDs the brighter the light. They are very efficient and some systems can be used with 240v mains electricity, 12 volt DC or portable batteries. The small size of LEDs means that they can be incorporated into housings with compact form factors, which can be used in confined or difficult positions.

Small and large light sources

The relative size of a light source to the subject has a strong influence on the appearance of the lighting. A small light or ‘point source’ has high contrast between shadows and highlights; shadows will normally have clearly defined or ‘hard’ edges. A large light source produces a much ‘softer’ light with less contrast between shadows and highlights. The Sun is a very large light source however its great distance from the Earth makes it behave like a point source. Light rays from the Sun travel parallel to one another, this produces clearly defined shadows. On overcast days the clouds disrupt the light rays causing them to travel in all directions, this produces less clearly defined or ‘softer’ shadows. Small light sources include flash bulbs, bare domestic light bulbs and candles. Large light sources include general office lighting, reflected or ‘bounced’ light and north light. It is normally reasonably easy to convert a small light source into a large one but quite difficult to do the opposite.

         
Left, direct light rays from the Sun produce hard edges shadows. Right, diffused sunlight produces softer shadows

Modifying light

The quality of light in the natural world and how it illuminates the subject varies according to the position of the Sun in the sky and the prevailing weather conditions. By carefully adjusting the position of the light/subject or using large or small light sources the photographer or filmmaker can also radically alter the appearance of the captured image.

Modifying flash

Most digital cameras have built in flash units, their proximity to the lens makes them hard to modify and they often produce images with hard-edged shadows. A loop of light diffusing material such as tracing paper attached to the built in flash might ‘soften’ the light a little, for greater control over flash lighting a separate camera mounted flash may be required.

       
Left, camera firing built in flash. Right subject illuminated by a direct camera flash. Note the sharp edged shadows behind the books.

Detachable flash units may be directed or ‘bounced’ off a large white surface like a wall or ceiling or through a sheet of translucent material such as tracing paper. This in effect creates a large light source, which is less directional and produces a more even illumination. A lot of the light is lost when it is bounced or diffused and the photographer may have to adjust the camera’s exposure settings to compensate. It is important to check that the surfaces used for bouncing lights are not coloured as the colour is also reflected onto the subject.

      
Left, camera with flash pointing at a white ceiling (bounced flash). Right subject illuminated with bounced flash. Note less obvious shadows and lower contrast.

By moving a large light source closer the lighting becomes softer and more of the light will reach the subject. Moving it away from the subject makes the light harder and less light will reach the subject.

Modifying daylight

Ambient lighting is the lighting that exists in a scene before the photographer starts work. Daylight is the most familiar type of ambient light but it is also the hardest one to control, it can’t be switched on or off and often the photographer must work with what is available or wait and hope that the light improves. With daylight we are unable to move the light source (the Sun) to illuminate the subject from the desired angle though we may be able to choose a time of day when the Sun is in the right place in the sky to light the subject. Alternatively we may be able to move the subject. Strong direct lighting can produce harsh shadows, to compensate (if this effect is undesired) the subject can be moved into shade or the light can be diffused. Shadows can be ‘filled’ with bounced light from a reflector or with a little light from a flash (fill in flash) or top light on a video camera. Before the widespread use of specialist lighting many photographers and artists used studios with large north facing windows (in the northern hemisphere) to take advantage of the diffused light.

 
Right, filming under direct light. Left, subject illuminated directly from above.

The image above shows how direct light creates high contrast lighting with very strong shadows.

 
Right, filming in direct light with reflector. Left, subject illuminated from above with reflector lightening shadows.

The images above show how a reflector can be used to reduce the contrast and ‘fill’ the shadows, stills photographers can use the camera’s flash instead, this is known as ‘fill in flash’. While there are lots of commercially made reflectors available, a homemade reflector made from a piece of white card, polystyrene sheet or flip chart paper will produce similar results. For the best results the reflector should be positioned in the light facing the side of the subject which was in the shadow. The reflector can be curved around the subject to wrap the reflection around more than just one side.

 
Left, filming in open shade. Right, subject in open shade.

Another solution is to move the subject into open shade, the lighting will have much lower contrast and exposure values will change dramatically. This option may not always be desirable or possible. Another solution is to place an opaque board or semi transparent material between the subject and the light.

The soft light we associate with overcast daylight is very hard to modify with reflectors. If harder more directional lighting is required it will probably have to come from an artificial source such as a flash. Clouds also tend to absorb more of the ‘warmer’ wavelengths of light which can give images a blue hue. Careful use of the cameras white balance controls should reduce this.

Other types of ambient light include moonlight, domestic, office and classroom lighting. While the intensity is typically much lower than daylight or flash some of the above methods for modifying can be used to alter the appearance of the light.

Conclusion

Thanks to digital cameras it is now much easier for the casual photographer or filmmaker to produce good quality images under a wide variety of lighting conditions providing a few simple precautions are taken. If light levels are low, which is common in a classroom or lecture theatre then long exposure times may be an issue. In video the gain can be increased or in stills the ISO can be raised to reduce camera shake though the quality of the final image may be degraded slightly. A camera support may also improve quality and reduce shake - see our Stands and Supports document for more on this. In some environments it may be possible to switch additional lights on or off to adjust the light levels or even move them  to concentrate attention on the subject.

Last updated: 11 January 2010
Published in: Digitising analogue media | Creating new digital media
Tags: digitisation | hardware | lighting | photography | supports and stands | tripod

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