Street lights used to have incandescent bulbs that shine off in a pale yellow color.
Some of these old street lights had a cup-like designed reflector; some others had a ruffle designed reflector that covered the bulb less.
The "ruffle" design are lifters that direct the light on to the street more efficiently.drios1
From looking at a few really old town pictures in an album at a library, it seems apparent in some way that the cup-like reflector ones once had a round glass shape covering the bulb.
The round glass is called a refractor. The refractor has prisms that distributes the light more evenly. It works in conjunction with the reflector.drios1
Purple mercury-vapor lights were common at some point since after they were installed. However, In the late 1980's, the brighter orange sodium-vapor lights became much more common as they began to replace both the purple mercury-vapor lights and the old-fashioned incandescent bulb ones.
I think that the purple flourescent lights you are talking about are actually Mercury Vapor lamps. I may be wrong though. I understand that floursecent lights were very popular up north. My experience has been in Texas. The orange lamps are High Pressure Sodium.*drios1
Many vapor street lights also have stickers with numbers on them. They are yellow most of the time, but can also be white.
The yellow stickers are for High Pressure Sodium lamps. Blue stickers for Mercury Vapor (bluish-greenish white light); Red stickers for Metal Halide (white light).drios1
Numbers that I have seen on these stickers: 5; 7 (most common); 10; 15; 25; 40. One street light that I have seen has a less common X1 on its sticker.
The numbers on these stickers identify the wattage of the lamp. 5=50Watts; 7= 70Watts; the X1 is 1,000 Watts.drios1
Older street lights, including vapor ones, don't seem to have these number stickers.
A lot of problems with these stickers. They fall off or fade, maybe the white ones you've seen have faded.drios1
In many cases, when an old-fashioned incandescent bulb street light is replaced with a vapor one, so is its holder if it is one of those shorter, fancier-looking ones with the S-curve design. The replacement holder is usually one that is more streamlined and lengthier.
Modern luminaires "holders" are streamlined for wind loading. The less wind load the luminaire projects, the less loading the pole and the arm need to handle.drios1
On certain vapor street lights, there is an extra attachment. It can appear on either the front of the streetlight or the back. Perhaps it is for blocking some of the light coming from it.
The designs of a vapor street light have changed in subtle ways over the years. My guess is that the longer-looking ones are the earlier ones, perhaps dating at least as far back as the late 1960's.
As everything else, back in the 60's the luminaires were built to last a very long time. Bigger housings dissipated more heat. It allowed the internal components (ballast that actually operates the lamp) last much longer.drios1
Since 2003, the vapor street lights were redesigned as such as now not having a bulging glass cover. The glass covers on the brand new street lights are flat.
The refractor was replaced with a flat lens in order to eliminate the upward light component of the luminaire. This type of design will eventually improve the light pollution that prevents us from seeing the stars. This type of luminaire is called "cutoff". The inside reflector was modified to improve the light pattern but they are not as effecient as the refractor.drios1
Especially since 2007, I started seeing flat glass streetlights designed differently. The designs of streetlights probably change one every few years.
In Brattleboro, Vermont, there are some streetlights that have an unusual design. These are also vapor lights, but are much smaller looking. They are shaped like short cylinders.
In my hometown of Greenfield, Massachusetts, the utility companies have installed new streetlights around April 1, 2014. They look like they are shaped a little bit like shoes. The lights themselves look flatter, and appear to have lighting that I never saw before, except for the same type of streetlights that were installed on Silver Street a few years ago (probably in 2011 or 2012), of which there are four. These Silver Street ones are a dark color. The new ones that have been installed lately are a light color. There appear to be at least two different designs. I have been told that these new lights are LED lights.
I had also been curious how they turn on when it gets dark. I was guessing that they start out a bit dim, then get to full brightness a few minutes later, similar to the spiral-shaped bulbs that seem to have replaced the conventional bulbs for house lamps. I was told, though, that they flicker when they turn on, like the vapor ones that have been used since about the 1960's, both the purple and orange ones. It's possible that I may have seen one actually turn on, when I saw one appear to do a slower flicker of off and on. I also heard and read from some sources that they just simply turn on, like the really old incandescent bulb lights that date before the vapor ones. These really old incandescent bulb lights are very hard to find on poles nowadays, since practically all of them have been replaced - at least in my area.
I eventually saw one of these LED lights turn on. From my experience, it appears that they just simply turn on, just like the old incandescent bulb street lights. In fact, in some ways, the LED lights sort of remind me of the old incandescent bulb street lights, especially when I look at them off in a distance, in which the lighting seems to resemble the old incandescent bulb lighting a little bit, except that the lighting of the LED ones are of a white color, as compared to the yellowish color of the old incandescent bulb streetlights. However, when I wear yellow-tinted night vision glasses as I'm driving, they seem to resemble the incandescent streetlights of many years ago even more.
Eventually, I started noticing LED lights having a few extra attachments added to them. At first, I saw only those made up of one big unit - exclusively on High Street in my home town. In recent months, similar types of attachments started to appear on the LED lights at other various streets. However, these are made up of three smaller units, with a rectangle box-like part attached at the end of the street light holders that are closer to the pole itself.