N
N9WOS
- Jan 1, 1970
- 0
Actually they aren't. They are very efficient. the lumens/watt isn't much
different between my 9 watt and my 25 watt CF's.
Fluorescent lights don't exactly follow the same rules that other lights do.
Other lights gain a performance advantage with size and wattage. The
elements are a lot hotter than surrounding temperatures. So, on a small bulb
with a small element, a large portion of the heat generated is lost to the
outside environment. It has to waste a lot more energy per lumen to maintain
operating temperature. When you increase the size, it's internal volume, to
outside surface area ratio goes up. The energy loss from the exposed surface
of the element is smaller in reference to it's wattage and lumen output, so
it wastes less heat maintain operating temperature, and efficiency goes up.
Fluorescent lights are not a lot hotter than their environment. What
determines their efficiency is the energy/current density of the discharge
in the tube. That determines how effectively it drives the phosphor on the
walls of the tube. You have a sweet spot. If you drop below that density,
the efficiency goes down. If you go above that level, efficiency goes down.
CF's from 3W to 25W usually have about the same lumens per watt because of
the fact that energy densities, and tube diameters are roughly the same for
all wattages. The more wattage, the longer the discharge tube. While the
factors that determine the efficiency of every inch of discharge tube is
about the same. The discharge current levels are at the maximum the
materials allow. They run the tube as hard as they can without destroying
the phosphors, to make the light as small as possible for the wattage it's
rated That causes efficiencies to be close to the bottom of the fluorescent
family. About 60 lumens per watt.
You have to start getting into the 32W T8's and up to the 110W T12 high
outputs to get a good gain in lumens/watt as compared to CF's
..
The linear T8's and T12's don't operate so close to the maximum operating
edge.
T8 15W lights run around 65 lumens per watt
T12 40W lights run around 75 lumens per watt.
T8 32W lights run around 85 to 95 lumens per watt. About 50% more than
compact fluorescent lights.
T12 60W lights run around 95 to 100 lumens per watt.
T12 110W lights run around 88 lumens per watt
If you go up to T12 215W very high output lights, you get back into the
current densities that you find in CF's tubes. A 96 inch 215W T12 is being
driven has hard as it can without destroying the phosphors. So you end up
with about the same efficiency as a CF. around 60 lumens per watt.