Can someone explain  what a programmed start is please sorry to be a bit thick but never heard of it before. The street?amps in my road start off white when cold gradually turning to a gold sort of color I think they ate HF ballasts but not sure. Any thoughts on them please. Finally happy new year to all x Hannah

As far as I know, programmed start applies only to electronic fluorescent ballasts and not HID ballasts. It is a fancy name for controlled preheat. The programmed start ballast only lights the electrodes much like a glow starter only it is timed for about 1-2 seconds and then the ballast cuts out the heaters and strikes the lamp. It makes starting much easier than the conventional method of cold starting a lamp (instant start). Additionally, programmed start ballasts often have an end of life protection where the ballast will time out on starting attempts after a set time, so it will not perpetually try to start a bad lamp.

Sol is right about programmed start fluorescent ballasts, the streetlights you notice changing hue is just the lamp (likely high pressure sodium) warming up. HPS lamps start a dim white/pink (in the case of mercury-free lamps) and gradually shift to the strong yellow "gold" you are referring to. The ballast is likely magnetic HX or CWA type. Though some new 100w and 150w HPS cobraheads use electronic ballasts like fluorescent but the starting method is the same as magnetic, HV ignitor

Yes and in the case of a magnetic ballast for high pressure sodium, there is an ignitor which sends a high voltage pulse to the lamp to establish the arc. Once that is accomplished, the ignitor shuts off and is not needed until the next start. For electronic ballasts, the ignitor components are integrated into the ballast whereas with magnetic it is a separate component wired between the ballast and the lamp (exact configuration varies). All flavours of HID (mercury vapour, high pressure sodium, metal halide, etc) are designed for long operation cycles and few starts. The typical street light will only have one start per day.

Can someone explain  what a programmed start is please sorry to be a bit thick but never heard of it before. The street?amps in my road start off white when cold gradually turning to a gold sort of color I think they ate HF ballasts but not sure. Any thoughts on them please. Finally happy new year to all x Hannah

The street lanterns on your road, have high pressure sodium lamps. When the lamp is cold, the xenon starting gas, is the only gas that ionised inside the arctube, giving a white light, and as the lamp warms up, sodium vaporised and they gets more orange color, finally reaches to golden color.

Thanks for all your replies you have answered my questions. I think the street lamps here are HF ones because when they put them in they were replacements for other high pressure lamps

There are electronic ballasts for HID lamps, but they aren't HF, but LF square wave. HF on HID lamps, would causes the discharge to resonate and overheat the arctube, shortening lamp life.

By just looking at the streetlight you can never tell the type of the ballast.
But in most cases you can tell, what type of lamp is there.

@dor:
It is true the HF drive asks for resonance problems, but there are ways to suppress them by adopting the drive frequency. But that makes the control quite difficult and tied to only narrow group of lamp types (with each lamp design you have to recheck, if the resonance suppression algorithm really works; the related standards do not cover this behavior, I even do not know, how that could be standardized).
So the only benefit of the HF drive is the soft switching of the ballast output stage, so associated low losses even with rather slow power components.
Because the development of the power semiconductors, the HF drive fell out of interest - the low frequency is always safe even without the tedious rechecking of the compatibility with every new lamp type (all necessary specifications are in the related standard, you do not need anything more), the efficiency lag (behind the soft switching HF type) was reduced by just using faster semiconductors (mainly diodes).

Almost all electronic HID ballast are high frequency saw wave, only the good quality and expensive ones currently use the low frequency square wave.

As far as I know, the high frequency were used just for HPS lamps, as the thin tube makes the lamp more robust against effects caused by the resonance. And the shape ios rather sinewave (as a result of filtering by the output resonant circuit - it's main function is to boost the voltage for the cold cathode mode, so to heat up the electrodes quickly after ignition)

Otherwise all MH are square wave. Of course, the square wave has a triangular ripple on it (as a result of the switching regulation concept), but that amplitude is rather small (the peak-peak is no more than 20% of the lamp current), so poses no problem.

Older low frequency ballasts (and all the automotive MH ones) have separated power regulation converter (regulates the lamp power - adopts the output current to the arc voltage) and polarity chopper, the newer design have both function integrated into one stage.

One of the last trick has really made the HF ballasts obsolete:
The use of the active power factor corrector means the intermediate DC voltage could be boosted to any value (of course, higher voltage would mean higher component rating requirement, so there is a limit). That means the required ~250V OCV (sans ignition pulse) for the start could be met still with just a halfbridge topology, that means the output stage suffice with only two power transistors. So the power stage becomes practically as simple as the HF ballast. Because the low frequency ballasting is simpler (no need to detect and counteract any resonance effects in the lamp), the LF ballast became cheaper at the end.

Since then other concepts, how to suffice with just a halfbridge power stage came as well, most prominent (for it's simplicity with modern components) is a kind of hybrid one: Ignition and glow (cold electrode) phase operates as a resonant output stage (so same as the HF ballast; so easy to make boosted voltage, even without the need to have the elevated voltage on the DC bus), after the electrodes heat up (so the arc voltage drops; normally that takes about a second upon ignition), the ballast switches to the low frequency square wave operation. The output stage then operates the same way as a class "D" audio amplifier, just the signal is only the square wave.
This is not possible to implement with classic electronic hardware (it would be too complex), but it is quite easy when using one of the microcontrollers (you need just a PWM modulator as a special HW; but in the past 10 years not seen any new microcontroller without such feature). As these devices cost just few cents and are anyway necessary for the protection features (the electronic maintain the arc so well, the EOL lamp would really have to explode to kill the arc, so EOL detection and shut down is a safety must there).

Wow there's so much more to it than I thought our street lamps take about 5 to 10 minutes to warm up. I think they probably use LF drives because they don't create any noticeable noise on LF or HF radio which I'm sure they would with yards of wiring between ballast and lamp

Its likely magnetic HPS, pretty much unchanged everywhere for the last 2-3 decades or so. Electronic HID ballasts for outdoor applications is still very minimal, much more prevalent indoors for systems using 39-150w ceramic MH

We had low pressure sodium here for years then they were replaced with hi pressure then after 2 PS3 years these were replaced with so called energy efficient lamps which I presumed were hi frequency ballast but now I think there are low frequency ones as described above

If you want to know whether you have magnetic or electronic ballasts in the street lights, you simply need to go under one of them at night when it is lit. Take a shiny metal object such as keys (or any object for that matter) and wave it underneath the light beam. If it is magnetic, you will notice the flash pattern as you wave it. If you don't see the flash pattern, you have an electronic ballast. That is at least how my electronic MH ballast works.

The ballast's output frequency does nothing to improve energy efficiency in HID, fluorescent becomes more efficient with increased frequency but thats it. And a municipality typically wont bother spending the funds to upgrade a magnetically ballasted fixture to electronic as the savings would be minimal. The only instance ive seen this happen is when they convert an entire system to a lower wattage, or a different type (ex. HPS to CDM). Also, once you exceed 150/175w an electronic HID ballast no longer offers any energy savings over magnetic, the losses are the same on both. The  electronic ballast may only be consuming 255w instead of 290w(magnetic) but the lamp is also producing equally less light (ive tested this with a quantum meter)