Lighting
for night shoots often involves adding interesting colors that show it
is night-time. A big part of that are streetlights.
Discharge lamps, the old sodium and mercury vapor lights, are rapidly being replaced by LEDs. It makes sense. LEDs are brighter, use less energy, and require less service. They typically have a “cool white” color with a color temp around 4K. The delta UV value seems acceptable without too much green. It is a much better color quality than the old discharge type lamps.
I would guess most gaffers like me are unhappy with LED streetlights. We love the look of sodium and the less commonly seen mercury vapor streetlights. I hate the color of LED streetlights. The orange of sodium vapor and the blue-green of mercury vapor make for dramatic colors on night shoots. LEDs are boring by comparison.It's ironic. I'm gaffer who is about better quality lighting but I don't like LED streetlights because of the better quality of light. I’m going to need to embrace the change. LEDs will continue to replace the old discharge streetlights. I’m guessing in the not too distance future it will be uncommon to see a sodium vapor or mercury vapor streetlights.
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PS: I already dislike LED street lights for filming. Lately, I have been noticing lavender (or purple) colored streetlights. The horror! I've been hoping that it is not a new thing. A street lit with lavender colored streetlights would look awful.
Doing a little research, I found it is not uncommon to see lavender streetlights but it is not the way they are supposed to look. The lavender lights are defective. A phosphor film on the surface of the LEDs has delaminated causing the color shift.
Here is the story and history behind the lavender streetlights:
https://www.businessinsider.com/led-city-streetlights-turning-purple-broken-tech-danger-2022-11
PPS: More than you ever want to know about gas discharge lamps on Wiki:
https://en.wikipedia.org/wiki/Gas-discharge_lamp
PPPS: Gels For Streetlights
There is a whole universe of gels for converting lights to sodium or mercury vapor. A common problem with these dedicated gels is excessive loss of output; often 2-stops or more.
A story from one of my first films. During camera test, we tried different sodium gels. The DP picked his favorite. Unfortunately, I didn't really notice that the gel reduced the output by over 2 stops! On our first night shoot, we were disappointed by the output of our maxi-brutes in condors because of the gel. It was a lesson learned.
Every gaffer has their favorite gels. My favorite for sodium vapor is Lee Apricot. It looks great. It's an awesome sodium vapor on tungsten heads. It works on HMI's and daylight sources, too, but it's not as effective.
For mercury vapor, my favorite is Lee Fluorescent 241. It's not as effective on tungsten heads, but looks great with HMIs.
PPPPS: Low Pressure Sodium Light
I was on a tech scout at a factory once. One specialized section was lit with low-pressure sodium lights. It is somewhat esoteric lighting. I'm not sure why it was ever a thing. Low-pressure sodium lights appear dim and emit only a few narrow frequencies of lights. Most colors actually doesn't exist in this light.
The DP liked the color but it was unsuitable for filming. We ended up turning off the sodium lights and lighting the scene with my lights, with sodium gels of course.