LED MYTHS &

FACTS



Soviet inventor Oleg Losev invented the first LED in 1927.

However, LED’s were not commercially used until 1968. The current blue version LED with phosphor over the top (it is the phosphor that creates white light) was invented in Japan in 1992.


If I have a 10watt LED it will produce more light than a 6 watt LED

MYTH – this is a major error made by most people. The most important factor is “lumens per watt”. Technology is moving ahead extremely fast in the LED development sector. If an LED requires 10 watts to power it, this does not mean that it produces more light than a 6 watt LED. Currently high power LEDs produce 120 lumens directly off the chip. Two years ago it was only 65 lumens per watt.


Tungsten filament lamps

Only 2% is turned into light and waste 98% of the energy as heat. LED’s produce approx. 30% light and 70% heat.


LED’s don’t produce much heat

MYTH – LED’s produce heat in a very confined space (the foot print of the LED itself). If the LED requires 6 watts to operate then about 3.6 watts is wasted as heat.


All LED’s are dimmable

FACT – BUT it is not the LED that is dimmed, it is the driver, which must be of a dimmable type. There are two main types of dimming systems: 0 – 10 volt and triac dimming.


You can connect a string of LED’s to a live driver

MYTH – (this is called hot plugging) if the LED driver is connected to the mains before connecting the LEDs, it will instantly output its maximum voltage and current thereby blowing up the LED’s.


There are two types of LED drivers

FACT – There are constant current and constant voltage. Constant current is used to wire LED’s in series. This is the way Christmas lights are connected. Constant voltage is used for LED’s that have a built in low voltage driver.


Any driver will power a string of LED‘s

MYTH – each LED has two specifications that must be taken into account. The first is forward voltage (vF) and the second is its maximum current rating measured in milliamps. As an example Cree manufacture the MTG-2 LED. It is a 6vF (forward volt) with a maximum drive current of 2000 milliamps, provided that the heat sink will not allow the LED to exceed 105°C at its junction point.


There is no benefit and it is too hard to wire LED’s in series

MYTH – there is a great deal of money to be saved by wiring in series. As the driver is a constant current device it will compensate for the volt drop in the cable as a function of its design. Therefore much smaller cables can be used compared to parallel wiring. Parallel wiring requires each light tting to have its own built in driver (a constant voltage device) plus it requires considerably larger cables (which makes wiring connections much more difficult) to compensate for voltage drop over longer distances.


I don’t need to worry about what polarity the LED connections are

MYTH – LED’s are a one shot opportunity to do it right. If the positive wire is connected to the negative side of the LED or vice versa it will seriously damage the LED. It may not destroy the LED immediately but it will certainly shorten the life of the LED and may reduce the light output.


I can use a transformer if I don’t have a driver

MYTH – A transformer is an AC device. It delivers alternating current, not DC (direct current). LED’s require a DC supply.