– . – Lighting With LEDs
Lighting With LEDs
“The real challenge of filming is creating a visual wonder within today’s ever tightening budgets. I find that by fostering mutual respect, cooperation and creativity with all concerned, we can achieve much more for less.”
I remember being mesmerized as a young boy watching sci-fi programmes on our black and white television. All those flashing light panels were amazing. Perhaps this is why I decided to become a Gaffer, because I then found out that the flashes were from an LED, developed by Nick Holonyak in 1962. Since then the LED business has grown to become one of the most exciting areas of lighting today. In 2009 people spent nearly $4.9 billion on LEDs and current forecasts are that this will increase to $15.3 billion by 2015. So what is a Light-Emitting Diode and why do people want to use it?
An LED is a semiconductor device more akin to a transistor than a traditional light bulb because they don’t have a filament and as a consequence don’t get very hot. Illumination comes from the movement of electrons releasing their energy (photons) along this semiconductor. A diode is a very basic type of transistor that allows current to flow in one direction, and a light-emitting diode (LED) produces light as the current passes through it; this is called electroluminescence.
The single most important aspect of an LED is its efficiency at converting energy, as much more goes towards producing light than heat. As semiconductor device costs have fallen, LEDs have become more cost effective and very diverse in their form; from outputs of milli-watts up to 5 watts that produce over 100 lm/w from a single white source. Halogen lamps, on the other hand, have an output of approximately 10-30 lm/w. It’s a measure of the efficiency of a lamp to include voltage, light fixtures, bulb placement, ambient temperature and the bulb’s age to measure the actual light output and efficiency. LEDs can last well over 10,000hrs, whereas halogen lamps have a life expectancy of normally no more than 2,000 hours. Although compact fluorescents are popular, their colour quality is not to everybody’s liking. These gas-discharge lamps use electricity to excite mercury vapor, producing short wave ultraviolet light that causes a phosphor coating to fluoresce, producing about 60 lm/w. As ballast is required for operation this increases its cost and environmentally they hazardous waste. These are not to be compared with the excellent dedicated, very high quality, fluorescent lighting systems being used in photography on a large scale.
LEDs used as lamps are normally arranged in clusters in a housing consisting of a beam reflector, heat sink and electronic driver. It’s debatable whether these types of lamps are capable of replacing halogens in the domestic and commercial markets just yet, and I do wonder if the marketing campaigns of solid-state lighting are outpacing development. Mind you, 255,000 LEDs have just been installed in the new Uzbekistan Palace of International Forums – so maybe an LED wall to change the mood of a room comes next!
In terms of photography, film and TV lighting, it is very important to achieve a high quality of CRI (colour rendering index) and CCT (correlated colour temperature in °Kelvin). A halogen lamp would have a CRI of near 100 and a CCT of 3200°K. There are problems with applying CRI to white light LEDs (white LEDs are normally produced by mixing Red, Green, and Blue [RGB] or by phosphor coating – similar to fluorescent lamps) as they can produce bluish, yellowish, or greenish tints. The naked eye can easily see this so that a colour correction filter can be applied – one with a greenish colour as it closely matches the peak sensitivity of human vision. Mind you, improvements in colour rendering are happening rapidly and now most LED lamps come in either warm white (3000°K) or cool white (6000°K) appearance, together with a range of distinct colours complimented by instant on, or in a few microseconds. Discharge lamps on the other hand need to have a warm up period. There are also infrared LEDs, which excel at illumination in night vision photography. The latest lamps have dial in colour correction from warm tungsten to cool daylight (saving gel costs and maintaining light level). They are also well suited as camera light mounts as they can run for many hours on a very small power supply, even AA batteries. As well as being very light in weight and cool to touch, they offer a flattering softish quality of light and can incorporate a flicker-free dimmer. This is apart from the length of the lamp’s life, the stability of output as the battery runs down, no glass envelope to break and no flicker problems for high speed photography!
One of my favourites is the larger panel type lights with rows of LEDs, which can be banked in DMX modules to produce larger areas of light, having sufficient power output to enable a diffusion frame to be placed in front which creates a much nicer, softer, wrap around effect. All this with the added bonus of being able to plug into a local supply! I may not be a young boy any longer but I am still amazed.
And as a bonus for the Sound Department, all LEDs are totally silent – even when dimming – and they need smaller generators. Furthermore, LEDs don’t attract insects! It’s perfectly feasible to light an interior scene totally with LED lamps, although for balancing bright daylight you would probably still need ‘the big boys’ outside windows as LEDs are no match for any lighting requiring more than a 2Kw. Lamp LEDs are changing energy consumption patterns and improving the wellbeing of our planet in a positive and more efficient way; they make photographic shooting greener ecologically and save in manufacturing energy. Transportation is minimized – they weigh much less – and maintenance is reduced because they are more robust. Recycling is easier because of their design and RoHS compliance is satisfied (Restriction of Hazardous Substances Directive). Because of this LED energy efficiency is far superior to any other form of lighting with the advantage of carbon footprint offset.
There is no question that LEDs will continue to radically improve and transform lighting. But despite this revolution in lighting advancement, LEDs still face the challenge of economic viability in order to attract the necessary sales volume, balanced against better performance, ecological and energy savings globally.
Brian Beaumont is a member of the Guild of British Camera Technicians. You can read fellow GBCT member Nic Lawson’s article on The Art of Good Lighting in movieScope 17