| Lets take into account only the intrinsic lifetime, so ignore all those early failures, which come from the quality control. Just because these apply for both fluorescent, as well as LED or any other.
First the F15T8 is not that much efficient tube: Tube itself needs 15W, gives off barely 900lm (in case of the tri-phosphor form; halophosphates are just around 700lm) and with the ballast losses consumes something between 18 till 20W. So something around 45 till 50lm/W (35..40lm/W for halophosphates).
Practically all decent LED's are around 100lm/W include ballast losses and effects of the operating temperature.
But the problem is elsewhere:
The LED tubes are either not fully optically compatible with the fluorescents, because they are designed for a given (usually office drop-in ceiling squares) style fixture, in other ones the light pattern does not match, so the final illumination is at least strange, if not even inadequate. Even when this use applies only for the higher power, longer tubes, for the lower wattages the makers use the same generic profiles, so a 15W replacement will be made with the same pattern as the F32 one, although that format does not make any sense with the F15 (there are no office squares using F15 lamps...)
There are optically fully compatible tubes on the market, but the compatibility costs on the overall efficacy (the required diffuser wastes some light), so these then do not offer that much of the energy saving.
And with both you should count the rather outrageous cost of those LED tubes, together with their rather short life (for a LED; given by the limited cooling possibilities).
So with the quite limited energy saving potential, I don't think using a retrofit tube within an existing fixture would ever pay off, both financially, as well as environmentally.
Other story would be, if the question is about a fixture to be still installed. There considering a LED batten (or what is the desired format) instead of the fluorescent may pay off: Taking all the light losses in many fluorescent fixtures, about 400..500lm (around 5W) of LED's will do the lighting job, but only when the fixture is really well designed around the LED's. There the thermal management could be very good and that should offer full life of the LED's in the 25+ khour (any statement above ~25khour is an unsupported nonsense - the technology is just not that long here to have really all important effects under control). Plus it should not suffer from frequent switching.
For such applications I would even consider the 12VDC stripe format (but installed in a proper heatsink batten), even when that means a bit lower efficacy. The point is, all the switching is done on the secondary, so no inrush currents there, so no switching wear or so at all. The drawback is the energy losses on the ballasting resistors (around 25% energy is wasted there), but on the other hand this format allows really efficient installation in the terms of light distribution over the area, what may compensate that back to quite big extend.
|
