About LEDs
How LEDs Work
The light from an LED is practically a pure, single colour. A green LED produces green light only, a red LED only red light, and so on. It is the material of the LED chip that determines the colour. LEDs are driven by direct current, and the amount of current determines the brightness. The brightness of the LED is proportional to the current flowing through the LED: more current, more light. In order to create a full range of colours including white light, we need to use a selection of different coloured LEDs that can be combined in various proportions to create a wide colour palette. Typically this is done using red, green, and blue LEDs. Yes, LEDs producing white light are also available. They use a technique borrowed from fluorescent lighting. White LEDs are actually blue or ultraviolet LEDs with a coating of phosphorescent material that shifts some of the light into green and red which, together with the original blue light, creates white light.
Lifetime
LEDs have no moving parts, no filaments to break, no arc gaps to erode, and no gases to deteriorate. They use very little power too. No wonder they are rated for up 100,000 hours. Imagine, that's 11 years if operated 24 hours a day, seven days a week. Unlike other light sources, the life of an LED is not determined by an outright failure to work. LEDs rarely go out with a bang; they gracefully decline over time. The single most influential parameter is the operating temperature of the LED and heat is the No1 enemy of LEDs. Most likely, your LED lighting fixture will be going (but not strong) after those 100,000 hours. Productive working life would perhaps be a better description. LEDs should be allowed to retire after a certain age.
What sort of lifetime can you realistically expect? A well designed LED-based lighting fixture should achieve at least 40,000 to 50,000 hours. That is still very impressive and more than enough for most real world applications; 24/7 operation at full power is rarely required anyway. Let's say there's three shows a day, each show at two hours, seven days a week. That's 42 hours of operation per week. If we conservatively assume 40,000 hours of lifetime, that translates into more than 18 years of operation.
Inherently Rugged
LED lights have one very strong and unique selling proposition: they are very rugged. With no moving parts, fragile lamps, or diachronic glass filters, no other colour-changing lighting fixture comes close to an LED-based unit in terms of ability to withstand abuse and harsh environments. This is a major benefit in the architectural market, but the raggedness is, of course, equally welcome in theatre and touring applications. LED lights can be built into set pieces and other hard-to-access positions. A current favourite application for LED lights is as truss toners. Mounted inside aluminium trussing, the small dimensions, rugged nature, and directional beam of LED lights really shine in this environment.
The Heat Is On
A significant feature and attraction of LED fixtures is that they radiate very little infrared heat (IR) together with the visible light. There is also a minimal amount of ultraviolet (UV) content from an LED fixture. This is of great benefit to applications such as museums, where there is great concern about long term exposure to heat and UV and the proximity of fixtures to the public.
A substantial amount of heat is produced inside an LED, and it must be removed and dissipated. Heat management is of critical importance, as LEDs must be kept within a certain temperature range, or the performance and life expectancy will suffer. Unlike tungsten lamps that perform best at literally red-hot temperatures, LEDs like to keep it cool and are very touchy about their environments. The heat stays in the LED chip itself rather than being radiated out along with the visible light. The beam of light stays cool, but heat is, nevertheless, generated. A well-designed LED lighting fixtures typically have substantial heat sinks or fans to help the airflow.