LEDs – Know the basics
From manufacturers to universities, LEDs are quickly replacing conventional light sources. Knowing a few basics may help you weave your way through this wave of the future. Here are lighting manufacturer Luxo’s suggestions for things you should know about LEDs.
An electronic component that generates light in a semi-conductor material. Under the right circumstances a diode may provide different wavelengths of seeable light.
- LEDs are not new.
Some people may recognize LEDs as being the red or green signal markers on hi-fi’s and TV sets—usually low-powered LEDs. High-powered LED costs have dropped in the past couple of years and operate at powers of around 1 W making them attractive to most industries. Forecasts show that by 2020, almost 50 % of all new and replacement light source unit sales will be based on LEDs–and because LEDs cost more than conventional lighting, the value of the LED sales will be even higher.
- LEDs last longer and don’t need to be replaced as often as most conventional lighting.
LEDs don’t have any movable parts or filaments to break so they last longer. This makes them very convenient with installations and replacements of challenging luminaires especially those at excessive heights and other difficult to service locations, e.g., windmills, telecommunication towers and chimney stacks.
- LEDs are more efficient than many conventional light sources.
All of the light emitted by an LED points in one direction allowing for less reflections inside the luminaire making them very suitable in situations where only downward lighting is needed. However, if both upward and downward light distribution is needed, the LED is less suitable, e.g., if compared to a T5 fluorescent lamp.
- LEDs offer new possibilities for color tuning to evolve.
Because LEDs are electronic components, they can be easily controlled (tuned) using software and control gear. An LED luminaire color can be mixed and may include red, blue and green diodes resulting in either colored light or white light.
The different color temperatures make it possible to produce cool and warm colored light. This capability comes in handy in office environments, schools and hospitals where concentrated light might be warranted, e.g., during a patient examination. LEDs can also be tuned to a warm temperature where more relaxing lighting may be desired, e.g., yoga cool down. This attribute is also being maximized to increase the growth of plants and reduce water consumption.
Heat management is the key to controlling the life of an LED and the temperature inside the diode. The temperature within an LED may get very high causing it to slowly emit less and less light. The higher the internal temperature, the faster the lumen degradation. Higher temperature on the LED chip (known as the junction temperature) speeds up the decline.
Lumen – a unit of luminous flux in the International System of Units, that is equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions.
- Understanding LEDs and lifetime, and diminishing output.
The amount of light from the light source at a future point in time is called the lamp lumen maintenance factor, or LLMF. The lifetime of an LED module is defined as the time it takes until its light output, or lumen maintenance, reaches 70% of the initial output (L70). This means the module doesn’t die instantly as do most conventional light sources; instead it slowly dims down. The luminaire industry has standardized LED lifetime L70 to a minimum of 50,000 hours. This corresponds to an LLMF of 0.7 as long as the lifetime of the lighting installation is set to the same amount of hours.
- The color spectrum of an LED comes from its color rendering capability.
Sunlight, halogen and metal halides possess complete spectrums while sodium lamps,
fluorescent tubes and LEDs have varying power distribution curves. Cool white LEDs have more blue light in them; warm white LEDs have more yellow and red light.
- The LED driver is the auto pilot of the LED luminaire. Proper drivers help LEDs to stay cool and stable.
LED drivers differ from conventional power supplies because an LED driver responds to the varying needs of the LED supplying constant amounts of power as its electrical properties change with temperature. Choices include constant current for serial connections or constant voltage for parallel connections.
LED driver advantages –
- Short response time – switches and dims immediately and can dim all the way from 0.1 to 100%
- Very efficient at producing colored light
Many applications warrant using LEDs, but not all. Analyzing the TCO when investing in LEDs including the energy costs, lamp change costs and cleaning costs can be crucial. Take time to consider all costs and suitable applications before making a final decision to transition or make new investments in LEDs.