DIYbanter - View Single Post

Andrew Gabriel

In article ,
writes:
FWIW there are thinner ones with better efficacy than T8 or T12 but their ouput v temp dependance is horrible

You are talking of T5 tubes.
T5 tubes are only rated for running on electronic control gear.

There are two ranges:
T5HE (High Efficiency) are exactly the same efficiency as T8, when
compared with T8 running on electronic control gear (although for
historic reasons, I think T8 efficiency still has to be quoted for
when running on magnetic ballasts, which is why it looks lower).*

T5HO (High Output) are lower efficiency than T5HE or T8 on electronic
ballasts, but significantly higher light output for when that's
required.

(There is also the old T5 tube range, 4,6,8,13W, but these are
separate from T5HE and T5HO ranges.)

Also, as I hinted before, there's an important difference between
fluorescent tube efficiency, and flourescent luminare efficiency.
Fluorescent tubes emit light all around the tube (excluding in-line
with the tube). That's not usually how you want light distributed,
so refectors are used (that can be part of the luminare, or
something like the ceiling - it doesn't matter). Reflectors are
inefficient, and even with reflectors, much of the light is lost,
typically 50% in the luminare and external reflectors such as
ceiling, although it can be much worse.

T5 tubes do make it possible to design slightly higher efficiency
luminares, because the smaller light source (thinner tube) makes
it possible to focus more of the light output in the required
direction than is possible with a T8 tube.

LED's on the other hand are by nature directional, so they start
off avoiding the problem of light leaving the source in the wrong
direction. They are (or can be) smaller sources too, which again
helps with any focussing optics to get the light in the required
direction.

* Also note that all T8 electronic control gear in the EU underruns
the T8 tubes, as is rerquired by EU directives, so that power is
saved rather than generating additional the light output which
would be achieved if they ran at high frequency at full power.
This doesn't significantly change their efficiency though.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]