I rounded the corner and was almost blinded by the (street)light. Ow. It’s bad enough with the vampire-slaying halogen headlights {great commercial] that wipe out your night vision for ten minutes, and that’s if they’re not on bright. And the Porch Lights of Doom that go off when a car passes by two blocks over. Now the street lights are out to get me!
There has to be a happy medium, somewhere. Not so dim that pedestrians are invisible and on-coming traffic vanishes, that you cannot see any thing at all. Nor so bright that they kill a driver’s vision and pedestrians* vanish unless they are directly under the light bulb.
Security says, “The more light and the better you can see, the less likely it is that Nasty von Badnick is going to be able to get you.” And there are advantages to being able to see people, dogs, or road obstructions like branches and holes. Streetlights have a use and I don’t object to them. Especially the older reddish-orange ones, which seemed a decent balance between visibility and excessive brightness.
The ones that surprised me are new, and I wonder if they are LEDs. They cast a very intense white light. It wiped out what remained of my night vision and I could not see anything past the light. Yes, we are talking the ones on the 20′ tall pole that shine straight down. I had a dreadful mental picture of someone pulling out in front of me, or a one of our cyclists rolling out to merge and my not seeing them. I’m not certain that the cure is worse than the problem.
Now, granted, I’m one of those people who would like to see halogen flood-lights go away yesterday, especially the ones aimed out and not down. If the big-box stores and mall removed their enormous, brilliant white, unshielded parking-lot lights, I would do the happy dance for hours while reveling in the no-longer-hidden starlight. I’ve had coworkers seriously wonder if I was a vampire, because of never seeing me by daylight.
However, casting a pool of light that conceals everything beyond it can’t be a good thing for safety.
*Sunday afternoon I did a major double-take because I saw a gent in what looked like Seljuk or early Ottoman clothes walking along carrying a long bag. Huh? Then I looked at the time: He was a local SCA member on his way to fighter practice, carrying his practice weapons in the bag. I bet the outfit was 1) to test it out during practice and 2) to help assuage concerns about what might have been in the bag. With his dark clothes and shoulder-length dark hair, he’d have been invisible once the super-streetlight wiped my vision.
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One reason the new street lights are so difficult is that they DO point straight down, whereas many of the old ones wholly or partially pointed out as well. I think the straight down ones are, theoretically, supposed to put all of their light where it is useful and make for darker skies… but as you say, they don’t need to be that bright to do it.
It seems that astronomers have lost the light-pollution war. I remember some years ago many cities were going to low-pressure sodium streetlights (the horrid yellow ones), so the stray light could be easily filtered out.
LED lighting has another interesting feature: looking through my glasses at an oncoming headlight, or at the LEDs on one of the panels in my shed, I see the blue pump wavelength offset significantly from the yellowish-whitish phosphor emissions. (Looking at it directly, sans glasses, I see, alas, only a blur.) I assume this doesn’t happen with mercury-type fluorescent light sources because in those the pump wavelength is UV, and the phosphor is providing the visible blue component at some wavelength closer to the other lines.
… Which would inspire me to break out a diffraction grating and have a look at some spectra, but they’re currently in storage in one of the many boxes of vaguely-sciencey stuff. And (checks price) nope, not going to buy a Chromation dev kit just for giggles; maybe if a business need emerges. A cheap eyeball-as-sensor spectroscope via Amazon, though? Yeah, I guess I’m curious enough now to spring for that.
And now I’m curious about why, if my glasses have so much chromatic aberration, I don’t notice it except when looking at white LEDs.
The LEDs are band-gap tuned for probably about 450 nm (need to look this up), to stay well in the blue color. It’s less efficient coupling to the white phosphor, but comes out ahead on lumens/W used because the diodes are more efficient at releasing light than a discharge tube. The diffraction, and I’ve seen it too, is caused by an odd-numbered Fresnel diffraction – generates more light along the main axis, but has some significant sidelobes and shadows. That’s due to physical construction of the diode layer, with phosphors and diffraction grating atop them. The diffraction and aberration get amplified because the source is a narrow-band blue light. Blue scatters very easily, which is why the sky away from ground and sun looks so blue. It explains why we see some bluish shadows and blue-white light leaking around the edges – it bounces and scatters off the light fixture and off molecules in the air. Not going into details, because that’s two pages of advanced math, packed in a box with other references.
Fluorescents use mercury vapor discharge in a tube. Phosphor is deposited uniformly around and along the tube, so you don’t see diffraction. If your eyes begin feeling grainy or dry, find someone in maintenance and have them check the lamps. UV energy is diffracting or leaking out, in that case, and one or both ends of the tube may look dark. You won’t see the UV, but will feel the effects like a slow sunburn. Mercury vapor has a strong discharge line in green, a weak one in blue, and a moderate to weak line in red, IIRC from an old p-chem lab; these are in additino to a very strong UV line. This is why they sold green filters for film cameras, or have fluorescent light setting on digital cameras now, to take out the greenish cast that makes images look bad.
I’m currently getting used to having to wear glasses most of the time.
It’s been a constant source of shock how badly they interfere with seeing much of anything in the dark when there’s a light source anywhere within the field of view.
I used to be able to read by the light of a full moon.
Now, I have to turn on the garage lights at high noon to walk through it without tripping. (Or just take off my glasses for a few moments. Depends on how full my hands are, really. But learning that truth was a bit painful.)
I used to use the auto-dimming Transitions lenses, but discovered they they take a really long time to recover in cold temperatures. A bright winter day meant I’d have to take the glasses off when I got into the poorly lighted barn. In the mornings, with no stove running, it could take an hour or so to recover.
Now, I use clear non-dimming glasses (no tint) and a pair of Old Man (trademark) sunglasses if necessary. It beats the alternatives. I’m also adding some light to the barn. 🙂
c4c
I don’t think the brightness has to do with them being LEDs. LEDs come in different ratings, differing amount of brightness and diffusion.
I’m the manager for a self-storage facility in a small city outside of San Antonio. We used to have the old sodium lights, and they were pretty bright. Bright enough that one of the owners, an airline pilot, could pick out this facility from the air at night when he was flying into SAT (and fretted seeing his money being transmitted into the sky). The lights were shielded at top, and had diffusers, but still they put out some lumens, especially reflected from the white concrete below.
He had budgeted for maintenance and improvements when he bought the facility, and when the time came he had all the sodium lights replaced with LEDs. I forget what the savings were but it was substantial, and the actual lighting is much more subdued than previously. You can still see but it is not the Texas Sun at High Noon brightness and glare of the previous generation.
And he feels better flying overhead. 🙂
Sorry, should have thought this out before double posting. One of the peeves with LED lights is that they appear way too bright, and can feel like you’re being blinded. The EEs who designed them answered only part of the question, the part about using less energy and getting higher efficiency output as a light source. They did not consider the receiver, which is the eye-retina-brain combination. You see something much brighter than intended. It’s not apparent until someone asks why.
The reflected or direct path light can seem blinding, because the blue-white light is transferred more efficiently to the reflectors and sent out. The received intensity appears higher, because the ‘white’ light has a higher apparent emission temperature. Indoor tungsten light is about 3500K, normal daylight about 4500-5000K (depends on cloud cover), and the LED lights are somewhere around 6000K; I need to run some Planck calculations to get a better figure. The retina and eye are most sensitive to light at 400-500nm; they transmit most efficiently through seawater, where eyes and optical sensors began. The LEDs look much brighter because they’re presenting a much brighter source to your eyes, something more intense than noontime sun, just where the eye has its most efficient response.
You get the energy savings, but then need to configure the lights so you don’t destroy night vision for people. A lower wattage equivalent may still give enough light from LEDs, but cause less night issues. That sounds like where Eric is seeing the energy savings and less glare.
I don’t know streetlights (the company I was working for was partnering with Phillips to do such, but that was before the dot-com crash in 2001), but LEDs for home use seem to come in 3+ color temperatures. 5000K, 4000K and 3000-2700K. The latter are decidedly YELLOW, to the point where if I’m trying to differentiate between off-white dog biscuits and yellow ones, it’s a crap shoot until I get a bluer light on them.
The shop light fixtures I got from Costco are running 4000K. Blueish, but not bad. Most of the bulbs in the house that replaced CFLs are 2700K. Spots and floods seem to be available in a variety of color temps.
The killer is high intensity and sharp edges on the light pattern, with no transition zone for your eyes to adjust. On a rural highway without streetlights, a traffic light can blind you at night, so you need to use your high beams to proceed safely.
I wonder how many highway engineers (or the people who write practices they are compelled to follow) drive the roads they design–or drive at all.
As to the shifting of images (chromatic abberation), back in the glory days of Scientific American I read an article to the effect that our eyes must correct for their own, so we have the means to do it. But I’ve seen the effect for many years with certain fluorescent-backlit store signs. It appears to depend on the exact spectra of the light, maybe the bandwidth, maybe the presence of certain wavelengths.
Agree with njc, and believe ‘part’ of the problem was the attempt to lower costs and extend bulb life. LEDs do both, but at a significant cost to us the consumer in our night vision.
Under Barttle Hall in Kansas City. Shudder.
And the worst part, as near as we can tell, they are only using about a quarter of the LED lights that they have mounted.
Update: I got my cheesy spectrometer by Sunday-morning courier. It’s not exactly a high-quality instrument, but:
The spectrum from an old-timey fluorescent tube looks fairly continuous (I’m sure a better instrument, or the same one with a better grade of eyeball, would reveal distinct spectral lines).
The spectrum from a spare LED panel has a definite gap in the blue-green area, and a strong component in the far-blue. Which might explain why the blue appears as a separate light when seen through glasses, instead of being the end of a smear. I’m sure a brainologist of some sort could explain how a color smear sans gap gets perceived as a single white light.
… That and, as others have suggested, the compactness and sharp-edgedness of the LEDs as compared to most other light sources.
I gotta admit, my gung-ho for this would’ve been a lot higher yesterday.
Before I found hte frame on my middle daughter’s window.
Bowed out where SOMEONE tried to pry it out behind the latch, not realizing there is a shaft-lock at the back, not just a latch.
Yikes! I have no problem with security lights, aimed properly and on timers, and we have two around Redquarters. (DadRed places a lot of trust in our alarm system. I sneak around and close windows at night.)
I don’t understand why a security light has to go off when someone is on the other side of the street, and shine out, not down. It would seem to leave shadows right where you least want them.