lunes, 2 de mayo de 2011

Controlling LEDs Part 5 - What type of LED product am I using: an LED lamp or LED fixture?

LEDs are low-voltage devices. Therefore, additional electronic components are typically required to convert the line-voltage power to a low voltage for the LEDs. These electronics may also interpret control signals, and dim the LEDs accordingly. These devices are referred to as LED drivers.

LED luminaires come in two distinct types: the LED bulb (also called an LEDi or retrofit lamp) and the LED fixture.

LED bulbs have Edison-base sockets and are meant to replace standard incandescent or screw-in CFL bulbs. The bases of these bulbs have integral drivers that determine if they are dimmable, and if so, what the dimming performance is.

LED fixtures can vary from cove lights to down lights and usually have an external driver. Some fixture manufacturers offer different driver options on the same fixture to support different control technologies or applications (such as dimmable vs. non-dimmable).

There are two different types of drivers. LED drivers may be constant voltage types (usually 10V, 12V and 24V) or constant current types (350mA, 700mA and 1A).
Just as their names would suggest, a constant current driver provides a constant current, such as 700mA, to a pre-made LED array that is designed to operate at or below that current level. This is great for a down light, sconce or other LED fixtures that use only one light source per driver (much like a fluorescent lamp with its associated ballast). Note that some drivers support multiple currents, making them more flexible when designing a fixture.

A constant voltage driver provides a constant voltage to one or more LED arrays connected in parallel. A constant voltage driver is used in areas where you may have a variable amount of fixtures, such as a cove or under-cabinet light. These are similar, or sometimes identical, to electronic or magnetic low voltage power supplies (such as those used with MR16 lamps) and often have 12V and 24V outputs.

These two types of drivers are NOT interchangeable, and it is the design of the LED array that determines which driver is appropriate. Often this is application-based, but it is still the configuration of the LEDs that determines if a constant current or a constant voltage driver is needed. Some drivers are manufactured to operate specific LED devices or arrays, while others can operate most commonly available LEDs. Additionally, the long-life benefits of LEDs would be reduced if the driver was not designed for an equally long life.

The instantaneous response of LEDs to changing current makes them highly susceptible to flicker, especially compared to incandescent sources. One of the most important LED driver features to understand is the quality of the DC output voltage of the driver. Finally, be cautioned that remote mounting of the driver could result in potential voltage drops, power losses, or noise susceptibility on the DC wiring that must be properly accounted for.

Extracted from "Controlling LEDs" Copyright 01/2011 Lutron Electronics Co. Inc. P/N 367-2035 REV. B