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Digital Ballasts - The Definitive Test
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Digital Ballasts – The Definitive Test
We’ve
heard it all about digital ballasts – from ridiculous performance
claims to unachievable physics, there seems no end to the fanciful
claims of some manufacturers. The list of so called experts who have
added their 2p to the digital ballasts debate seems to grow by the day,
so in search of some definitive answers we have decided to carry out
some tests.
Background
In order to understand our test results, you first need to fully understand the mechanics of how a ballast and lamp work.
High
Intensity Lamps such as the Sodium and Metal Halide lamps that are used
in grow lights need a ballast to regulate the power supplied to them.
Without a ballast to control the power to the lamp, it would simply
draw massive amounts of power and instantly fail. This is why you need
to match your 600 Watt Lamp with a 600 Watt Ballast – so that the right
level of power is supplied to the lamp and that the lamp itself is not
damaged.
HID Lamps have a band of operation at which they will
perform to their optimum level, the gases within the lamp will ignite
correctly (providing the intended colour of light) and no unnecessary
damage is caused to the lamp. In a 600 Watt Sodium Lamp for example,
this range is from 580-660 Watts. Any further power to the lamp and you
risk damage and the colour rendition from the lamp will not be as
intended. You may achieve higher overall light output from lamps that
are overrun above this safe level, but it will be expensive both in
terms of electricity used and the need to replace your lamps more
often. It is therefore very important to provide consistent power to
your lamp within the safe range of operation for that lamp.
How traditional (magnetic) ballasts work
You
may have heard a traditional ballast referred to as “magnetic” or “core
and coil”. This is because a traditional ballast regulates power to
your lamps by means of a coiled wire around a metal core. This creates
a magnetic field (exactly like an electro magnet) which restricts the
power allowed to reach the lamp. In very basic terms, the ballast is
designed to balance against the pull of the lamp so that the correct
level of power ends up being supplied. This method has worked very well
for a very long time, but there are a number of flaws in the design.
To
accurately regulate the power to the lamp, the ballast is designed on
the assumption that the input power will always be constant. In reality
this is not the case. Everyone knows that UK mains power is supposed to
be 240 Volts, but in truth this can range from between 215-260 Volts
depending on your geographic location, the time of day or even how many
lights you have on the same circuit. What this means is that your
traditional ballast (which is designed to provide 600 Watts to your
lamp when it has a constant supply of 240 Volts) will actually supply
varying levels of power to your lamp depending on the incoming supply.
This is bad for the lamp (as it will degrade faster) and is also bad
for your plants as they could be missing out on valuable light.
Another
drawback of magnetic ballasts is that over time they will become less
and less efficient and supplying the right power to your lamp. They
will draw more power (costing you more on your bill) and will not
correctly regulate the power to your lamp (meaning that you may have to
replace you lamps more frequently).
How digital (electronic) ballasts work
The
purpose of an electronic ballast is exactly the same as a traditional
ballast – to regulate the power to the lamp. The way in which it does
this is very different though. Rather than pulling against the draw of
the lamp, an electronic ballast regulates the power supplied to the
lamp via circuitboards and microprocessors. In practice what this means
is that they supply exactly the desired power to the lamp (in the case
of the Lumatek ballasts exactly 600 Watts to a 600 Watt Lamp). There is
no loss of efficiency over time either – a 5 year old Lumatek will
still supply exactly 600 Watts to the lamp just as a new unit would as
it will not lose efficiency over time like a magnetic ballast will.
This means that your lamps will always provide the correct colour and
will last longer thanks to consistent supply well within its safe range
of operation.
Electronic ballasts are extremely efficient. In
our tests, the Lumatek ballast “lost” very little power between the
wall and the lamp. The Watts of electricity drawn at the wall for a
Lumatek 600 Watt ballast is 634 Watts – meaning that just 34 Watts are
lost between the wall and the lamp. On our magnetic ballast tests, much
more power was being consumed (especially with the older ballast) and
the electricity bills associated with using these units would have been
considerably higher than the equivalent electronic unit. Typically, a
brand new magnetic ballast supplying the exact same 600 Watts to the
lamp would “lose” between 50-60 Watts between the wall and lamp in the
form of heat, noise and vibration. This amount of ”lost” power
increases as the magnetic ballast ages.
Electronic ballasts also
compensate for fluctuations in the supply – so unlike the magnetic
ballast where light output can vary depending on the incoming voltage,
the Lumatek will stay consistent no matter what happens with the
supply. Your lamp output will always remain the same no matter what
time of day or where in the country you use your light.
Increased Lamp Efficiency
Digital
ballasts aren’t just more efficient at regulating the power to the lamp
– Lumatek claim that they also operate your lamps in a more efficient
way than a magnetic ballast and actually achieve a higher lumen output
per watt.
A traditional magnetic ballast turns your lamp on
and off 50-60 times per second whilst a digital ballast turns your lamp
on and off approx 40,000 times per second. Lumatek claim that this high
frequency lighting excites the gases in the lamp more efficiently and
produces more Lumens per watt. At 50-60 times per second the amount of
power the ballast provides the lamp (lamp power) is directly
proportional to the amount of light it produces i.e one magnetic
ballast providing 600w to the lamp will produce exactly the same light
output as another that provides 600w lamp power. This is not the case
with the lumatek ballast. For the same lamp power provided to the lamp
the Lumatek increases efficiency by approx 5%. Combined with the better
power management this gives efficiency gains by the Lumatek in the
10-20% range over magnetics (depending on voltage). At the time of
writing, we have not been able to independently verify this additional
lamp efficiency data, but given that all of their other claims have
stood up to our tests with regard to power management then we have very
little reason to doubt that this is also true.
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