# Talk:Halogen Lighting

## Propose move

to Halogen, with this article becoming a link to there. It'll make life significantly easier in time. NT 09:02, 1 March 2009 (GMT)

since google seems to be getting flaky on groups searches, I thought it work keeping this post from Andy Wade on transmission line losses to be integrated at some point:

There's a current loop of finite size, so the inductance is finite, not zero. Whether or not it's vanishingly small depends on the application.

``` In 50 Hz work we're used to being able to neglect wiring inductance,
```

but it ceases to be negligible at higher frequencies, or even at 50 Hz for large cables (50mm^2 upwards, say). In this case the frequency is over three orders of magnitude above mains frequency.

> How do you get your 0,9uH figure?

Any text book on E-M theory /transmission line theory will give you the following expression for the inductance per unit length of a parallel-wire line

```     L = (mu / pi) * ln (s/r)    [for s >> r]
```

where

```     mu is the permeability, in this case = mu_0 = 4*pi*10^-7 H/m
(so mu / pi = 0.4 uH/m),
s is the spacing (between centres) of the conductors, and
r is the radius of each conductor.
```

For 1.5 mm^2 T&E cable the wire diameter is 1.38 mm, so r =~ 0.7 mm. I guessed s = 6 mm.

Substituting these values, the ln() term evaluates to 2.15, so

```     L = 0.4 * 2.15 = 0.86 uH/m.  QEF.
```