LEDs
A ‘light-emitting diode’ (LED) is a piece
of silicon that emits light when power
is applied. They can be made in various
colours and initially were very low in
light output.
Modern LEDs have reached the point
where they can replace existing lighting
sources. They claim longer life and
reduced power consumption but there
are some limitations and some traps
worth knowing.
LED lamps tend to have wider beam
angles than dichroic lamps and most
230V lamps are not dimmable. The light
output can be less than the lamp they
replace, so check before you buy.
LEDs produce light once the voltage
across the silicon diode reaches a certain
point (forward voltage, or VF). Thisvoltage ranges from 2V to 3V and the
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doesn’t produce more light ... it simply
gets closer to point of the magic smoke
escaping, which stops it working.
Many LED lamps consist of a number
of individual pieces connected together
and some form of current limiting so they
can be connected to a voltage source.
Unfortunately, the manufacturing
process means that there are slight
variations in each LED, and each will
have a slightly different VF and current
requirement.
Unless they are all batch matched
before assembling into the lamp, you’re
likely to have some working harder than
others and the chance of early failure
is possible. The cheap battery-powered
torches with multiple LEDs are even
cruder with series and parallel strings of
LEDs and a single resistor!
To get more light and remove heat,
manufacturers have turned to chip-on-
board (COB) designs. See digikey.co.nz/
en/articles/techzone/2016/aug/the-
basics-of-chip-on-board-cob-leds for more
information. fMake sure the lamp wires
are in the secondary sideLeft: Tungsten transformer with mains on left
and single output connection on right
Below: The fitting before removing
(and cleaning)