Other 230V products, such as bulbs, may condition the supply internally in order to supply the low dc voltage that the LEDs require. These products will often respond quite well to the higher quality thyristor dimmers, which chop the supply. Because of the large number of LEDs in the chain, the resistor forms a relatively minor part of the circuit and so a voltage dimmer will have limited success. They will also have rectifiers in line to alter the supply to half wave.
This conditioning may prevent the bulbs from being dimmed using the supply voltage.Ģ30V products containing many LEDs may have their LEDs arrange in long chains similar to low voltage dc products. The LED lights designed to retrofit into these low voltage lighting systems contain electronics to condition the 12Vac supply so that it is suitable to drive LEDs. This is designed to work with traditional lamps and may work with LED lights. This means that when connected to a thyristor dimmer they transmit the ‘dimmed’ power cycle through to the load at the reduced voltage. Some of these transformers are electronic and state that they are dimmable. A lighting transformer is used to derive the low voltage from the mains supply. Low voltage lighting systems operate from 12Vac and there are LED replacement bulbs that will also operate from this type of supply. If you drop the supply below the minimum then the unit will simply cut out. Most dc supplies are rated to work down to 100Vac and so the dimmer will have no effect. There is no point in connecting your 12V or 24V power supply via a mains dimmer this will only alter the input voltage not the output. There is a bottom limit where the voltage is no longer high enough to maintain the necessary forward voltage across the LEDs and dimming will quickly change into the off state. Therefore some dimming can be achieved by lowering the supply voltage.
#WHICH DIMMER FOR LED LIGHTS SERIES#
An LED lighting product will consist of a number of these individual, series connected, LED chains.īecause of the resistors in the chain of LEDs, the whole product can, to some extent, show the characteristics of a resistive load. The value of the resistor is dependent on the particular LED and supply voltage. In order to make the supply standard, and independent of the basic LED, a number of LEDs (3 for 12V, 6 for 24V) are connected in series with a balancing resistor. Constant current supplies are relatively expensive so conventional medium power LEDs are still operated from constant voltage supplies. The voltage across an LED is dependent on the manufacturing process, chip size and colour, but lies in the region of three to four volts. If this current is lowered then the LED will dim. The latest high power LED light engines actually operate from constant current supplies. So the voltage across the LED essentially has to remain constant and the current has to be varied in order to dim. The V/I (resistance) curve of an LED is very steep, this means that for a very small change in voltage there is a large change in current, and therefore in light output. LEDs are like fluorescent lights in that they need a fixed voltage to operate, so if you employ a conventional voltage dimmer they will very quickly cut out.
If they present a resistive load (linear or non-linear) then if the voltage is reduced (usually a simple thing to achieve), the current reduces, hence the power and light output reduce and dimming is achieved.
Lights are designed to work on a particular typical/maximum voltage, on which they draw a particular current.They therefore have a particular power and light output rating. As a result the circuit in which it is to be used has to be designed for a specific type, size and colour of LED. This also affects the manufacturing process and the voltage the device operates at. The colour of an LED is set by the particular chemicals used during the fundamental manufacture of the device. The colour of an LED is not an after-thought added in the final stage, or even after manufacture as it often is with other types of light. It is manufactured in a totally different way to conventional lights. An LED is a semiconductor device, just like that used in microchips and electronic equipment.
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