compact fluorescent street lights

Ben formulated the question :

Are you sure they are compact flourescents? More likely they will be high pressure sodium which is much less yellow than the low pressure.

If efficiency was the only concern, low pressure sodium would still be used everywhere. Generally however, it's being slowly retired. The lower powered low pressure sodium lamps are not as efficient as the larger ones in any case, and there probably isn't a large difference between them and compact fluorescents.

On Sun, 26 Aug 2007 19:36:46 +0100 someone who may be Ben wrote this:-

How do you know they are compact fluorescent?

Generally low pressure sodium street lights are being replaced by high pressure sodium, which these days gives almost as white a light as mercury lights (also called fluorescent lights).

The high pressure lamps are not as efficient as the low pressure ones, but the light colour is a lot better.

================================== A reflection on our changing world. The yellow sodium lights were introduced (in part) because the yellow light was better able to penetrate the smogs of the 1940s and 1950s.

Cic.

There are white sodiums now.

NT

I think you will find that's a myth.. there is little evidence that yellow light penetrates fog any better than white light does. If different coloured light did penetrate fog better then all lights would appear to be colored in fog.. which they do not.

================================== Smog - not fog.

Smog was the name invented for the combination of heavy air pollution (from coal fires etc.) and fog. Any one who lived through the great smogs of the mid 20th century will remember road junctions marked by flaming oil lamps because the white lights of the time were totally ineffective. Myth or not, sodium lamps were considered to be the answer at the time. Fog is basically white - smog was dirty yellow / brown and almost opaque.

Cic.

ISTR learning that sodium street lights were first used commercially in the Netherlands where Philips developed them; and then in the UK on the Purley Way near Croydon Aerodrome in the early 1930s. That wd be an exceedingly odd place if their purpose was to counter the effects of smog. Also the output from gas lamps of the kind common in London was, according to my quondam tutor, often pretty much yellow (with the mantles in use at the time) in any event. OTOH I can well believe that their introduction was spun with any argument against those who hated their colour.

My memories of gas lighting (C1950) was it having a greeny colour as compared with the incandescent lamps of the day. I much preferred the gas lights.

An advantage of sodium is that it has an (almost) single chromatic line, thereby reducing chromatic aberration, benefitting some people.

Chromatic aberration used to be a problem with thick spectacle lenses. the modern ones have much less dispersion. At one time I could inspect the spectrum of street lights by viewing out of the edge of my specs. No longer is it possible.

So the advantage of sodium lighting is much reduced in the above circumstances.

================================== It appears that the Philips company installed some (about 60) sodium lights in Purley Way, Croydon, Way on the 8th December, 1932 as a demonstration. This was obviously a marketing exercise so not really a proper introduction. Without being unduly cynical I think this would have been an ideal place to show them off since there would have been no nasty air pollution around to spoil the effect.

I don't recall seeing them until the late 1940s / early 1950s but of course they might have appeared earlier in other areas.

The light from early gas lamps was really quite poor, giving just a small pool of light, with complete darkness outside the immediate area. My recollection is that the light was usually a pale bluish white but its appearance would have varied according to weather conditions - almost invisible in smog.

On Mon, 27 Aug 2007 08:48:14 GMT someone who may be Cicero wrote this:-

That would be mercury lights, not sodium.

there's still a pub round here that has gas-lights inside, they are a bluey-greeny white, then again this is natural gas rather than town gas they're burning.

Yes, and nice they were too. Brought real character to the place.

Where I lived, a little man with a ladder used to come round every few weeks to clean the glass, adjust the works and wind up the clockwork timer. His name was Frank.

Nowadays there are those revolting orange things and no Frank.

Bit of a myth. At one time car fog lights were yellow too. But that's gone out of fashion.

Sodium street lights were 'yellow' because that was the extent of the technology in those days for high efficiency lamps. They are diabolical devices which make it impossible to tell the colour of a car or road sign etc so were rightly superseded as soon as better technology became available.

One interesting point is they prove we don't see colours as the same within our brain. They are a narrow spectrum light and if an individual matches what they see with wide spectrum light - ie a mixture of red green and blue, they will get a totally different result from another. It's fun to try. ;-) You can do it with a computer monitor.

================================== Not entirely myth because it was the informed opinion at the time. All those gadgets for car headlights (clip-on amber headlight lenses, amber colour wash, etc.) really proved that there was very little practical advantage in amber light over white light especially as you had to remove them as soon as the fog / smog disappeared.

Colour perception is always a bit subjective, particularly in artificial light. I believe it's a common shoplifter's defence -"I only wanted to see how the diamond ring looked in daylight, Your Honour".

Cic.

In daylight when they are switched off its clear to see that they are fluorescent, the fairly long stick type like the household ones were a number of years ago before they made them shorter. At todays lengths I'd estimate they are about 50W.

I'm familiar with the difference in colour (and bulb appearance) between low pressure and high pressure sodium. When switched off its clear to see that these are fluorescent.