1

The Environment / LED streetlamps - effect on wildlife?

« on: 15/02/2014 11:30:23 »

I believe it is well-known that streetlamps do affect the behaviour of wildlife, including birds.

I hear local council (in particular, Cllr Mathew Shuter) has been seriously considering replacing all the streetlamps in Cambridgeshire with LED lighting (the present installed base is dominated by low-pressure sodium, with some high-pressure sodium on a handful of more main roads). Presumably white LEDs (which also have a pronounced blue peak in their spectrum).

Although the LEDs will give vastly superior colour-performance, sodium is reasonably efficient and simple and reliable; I'm skeptical that wholesale replacement with LED is actually a smart move. It seems like the current plan is to hold off for a few years yet.

Given the relatively recent discovery of the effect of blue wavelengths in setting human biological clocks / circadian rhythms, I wondered if there's potentially big effects "unforeseen consequences" on wildlife of replacing the orangey sodium lamps with white (and strong blue) light...?

Does anyone know if there is any research? Should the council be more formally advised that this is a potential issue?

2

Physiology & Medicine / Re: Do Light Emitting Diodes emit light that damages the retina?

« on: 30/05/2013 10:40:20 »

I've read that LED's produce light with a "blue glare" that can permanently damage the retina. Is this true? If so, what might we do to protect ourselves?

"White" LEDs normally comprise an actual blue LED coated with a white phosphor. The spectral output typically has a pronounced blue peak (and you may get more dominantly blue regions at the edges of the beam if the phosphor coating isn't uniform.
See https://en.wikipedia.org/wiki/File:White_LED.png
I think it unlikely that this residual blue would cause any lasting damage in practice (unless they were extremely poor quality LEDs with terrible phosphor coverage).

Fully fledged high power blue LEDs (1 to 3watts or more) will cause after-images on the retina if looked at for a few seconds - and this isn't recommended!
The hazard with deep blue LEDs is that the eye isn't very optically responsive to blue, so the damage potential can be much greater than it looks.

3

Geek Speak / What's going on with the Windows calculator?

« on: 28/05/2013 23:46:17 »

I just noticed some weirdness with the Windows calculator.
If I enter the following numbers, then press [1/x]   (that's the reciprocal button) I get:
5666.0   -> 1.7649135192375573596893752206142e-4
5666.1   -> 0.0001764882370590000176488237059
5666.2   -> 1.7648512230418975680350146482652e-4
5666.3   -> 1.7648200765931913241445034678715e-4
5666.4   -> 1.7647889312438232387406466186644e-4
5666.5   -> 0.000176475778699373510985617224036
5666.6   -> 1.7647266438428687396322309674231e-4
5666.7   -> 1.7646955017911659343180334233328e-4
5666.8   -> 1.7646643608385685042704877532293e-4
5666.9   -> 0.0001764633220985018263953837194939
5667.0   -> 1.7646020822304570319392976883713e-4

That's odd. Why do certain numbers not appear in scientific (e-4) notation?

Is there a bigger pattern to this?
Is this purely a display-bug, or is this the tip of a bigger iceberg?

Do you see the same? On what Windows versions?

I'm on Windows XP (sp3, on an old Pentium4 processor)

It doesn't seem to matter whether the calculator is in the "scientific" or "normal" mode.
Working with the same numbers, but x10 bigger (i.e. 56660 ... 56670) and again taking the reciprocal gives similar, yet subtly different results again! 

4

Technology / Re: Are cellular telephone towers safe to install in schools?

« on: 21/05/2013 00:05:59 »

There there no proven mechanism for harm at the levels of radiation permitted by law, and in any case, field strength decreases as 1/d^2. (Installation engineers are typically advised to avoid an exclusion zone of typically 3meters immediately in front of big cellphone-tower antennas). I agree with evan_au, that yes, if mounted on the roof then nearly all the signal will go out over their heads anyway.
Another consideration is that the nearer the base-station to the users it serves the lower transmit-power the handsets have to use during conversations... (and the longer the battery/talktime will last)

How many people that "worry" about phone base stations have a WiFi router (100mW, typ) sat right next to their computer/bed/sofa?   Remember the 1/d^2 rule...

We have a base station at work and if you deliberately go up the staircase in the building opposite, so about 10metres in front of the antenna and only slightly below (about 1 floor down), you get about -26dBm RSSI on phone (I admit I'd be less happy having my desk right there!), compared to around -80dBm for a typical "good" phone signal a mile or so from base. But even another 20-30metres away, off axis, the signal is a much lower -55dBm or so. (note dBm is a log scale!). Point being, the antennas are very directional, and in a more normal rooftop installation, the signal really can be expected to go out "over your head" - think of it a bit like the beam from a lighthouse!

5

Technology / Re: How do you describe a Transformer?

« on: 20/05/2013 23:55:28 »

And in practice (especially in transformers with small-numbrs of turns), because of leakage inductance, you might find that the voltage ratio isn't /precisely/ what you expected it to be.

I prefer to express my transformers in terms of a turns ratio m:n (where m is the driven side, and n the output side). This way a transformer used in a "step up" configuration can be written 2:20 (for example) in a logical (left-to-right flow) order without any potentially-misleading implication of fractions...

6

Technology / Re: How to make a safe mobile phone for people driving?

« on: 20/05/2013 23:36:22 »

Being a geek, and prone to have deep conversations, I can attest that having a cognitively-demanding conversation with a passenger in a car is also detrimental to my driving. I rarely have passengers, and having experienced the effect I will try to avoid such conversations in future too.
(With regard to driving while talking on the phone -which I absolutely do not do- ... Besides the fact that the other party on a phone can't see you and is therefore "unsympathetic" to the conditions, I suspect that struggling to hear them over the background noise and over a poor quality phone link also takes more brain-power away from the driving.)

7

Question of the Week / Re: QotW - 12.01.08 - Do sunglasses cause sunburn?

« on: 08/05/2013 22:02:20 »

It could be more harmful to the eyes to wear sunglasses than not *if* they are poor sunglasses which cut the visible light (making the pupils dilate somewhat) but don't block the harmful UV to the eyes very much.

8

Technology / Re: Can you still get bread sliced to order?

« on: 08/05/2013 21:57:12 »

Same concept, even more retro: http://f1.ehive.com/3021/1/1qb978e_127h_l.jpg

Interesting your mention of bread bought sliced to two thicknesses. Never seen it here (in UK). It's odd how some concepts catch on and are common in some countries, and not at all in others!

9

Technology / Re: Can you still get bread sliced to order?

« on: 08/05/2013 21:52:55 »

My parents have always used a hand-operated bread-slicer; cuts single slices at a time. Theirs was a 1970's one, but very similar in principle to this more modern one (image found on Google): http://1.bp.blogspot.com/_2rkC4S4huMQ/S8r_FOVcH7I/AAAAAAAAAS8/P7qz1E9jfsQ/s1600/Beans+and+bread+machine+Apr+10+006.jpg

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Technology / Re: Did you know that grid frequency can be used to authenticate CCTV timestamps?

« on: 08/05/2013 21:42:36 »

Besides their archive only going back 5 years, the technique is probably only applicable to recordings made using crystal-locked "digital" means - analogue recordings on tape would likely not be stable enough to recover the tiny variations in the 50Hz signal with sufficient accuracy.

11

Technology / Re: Can a microwave oven interfere with wireless headphones?

« on: 08/05/2013 21:37:12 »

Even when operating normally, microwave ovens can be expected to leak a small amount of microwaves (enough to be detectable with the right equipment, and potentially enough to cause interference to nearby radio devices operating on a similar frequency, 2.45GHz, but not enough to be harmful to humans or to cause permanent damage to other electronic equipment).

12

Technology / Re: Can a microwave oven interfere with wireless headphones?

« on: 04/05/2013 00:07:41 »

In short, you may experience temporary interference (cut-outs or garbled sound) while near the operating microwave, but you shouldn't suffer any permanent damage to the wireless headphones (unless the microwave is seriously damaged/faulty).

13

Technology / Re: Why 50/60 HZ AC?

« on: 04/05/2013 00:04:26 »

I'm not convinced by "DC transmission lines are also immune to space weather."
I can see the fault scenarios are a bit different, but I suspect 'immunity' is rather strong.

14

Technology / Re: Electrical Network Frequency analysis

« on: 03/05/2013 23:56:56 »

Yes, this surfaced in the technical press a few months ago. Using the 'fingerprint' for forensics is a neat idea.
However, I'm fairly sure a technically competant person could remove, conceal, or fake the signature. The police would still need to be certain the "evidence" could not have been tampered with.

For fun, you can see a "live" gauge of the grid frequency at http://www.dynamicdemand.co.uk/grid.htm    (I suspect this meter is delayed by a few (tens of) seconds though)   It doesn't keep in perfect step with measurements I make locally!

15

Geek Speak / Re: Which antivirus is best?

« on: 03/04/2013 23:43:33 »

I'll give another vote for eSET / NOD32  I've been using it for years - definitely less of a system-hog than Norton/Symantec!

16

Technology / Re: Can one put a mercury thermometer in the microwave?

« on: 24/03/2013 12:32:16 »

Bad idea, as the others have said. Significant risk you'll overheat the mercury (and get an invalid reading) and you might well break the thermometer.

Don't use an electronic thermometer either as you'll probably see sparks and kill that pretty much straight-away too.

17

Technology / Re: Have old Motorola phones suddenly become obsolete?

« on: 24/03/2013 12:27:50 »

Three old Motorola phones used by members of my family (two T180 and one V547) have as of late Saturday been unable to make or receive calls, though text messages still work. The fault is not in the sim cards - moving them into another make of phone is all it takes to get them working normally. The network is O2 and O2 says there's nothing wrong with it, though they won't say if they've changed anything.

I doubt many people are still using such old phones, but if anyone has one of the models of phone named at the top I'd be interested to know if it has developed the same problem or if it works normally, and which network you're using it on.

I know you said they're working again now. Phones of that era will be 2G (GSM). If they send/recieved SMS then they're on the right waveband etc. Sounds to me like O2 made some kind of software "update" in their system which was incompatible with your Motorola phones' voice/telephony system. Who knows which system (if either) was in the wrong (violated GSM standards) - but if it affected enough people / O2 got enough complaints, I imagine they'd roll back the upgrade quite swiftly... (which it sounds like they did)

18

Physiology & Medicine / Re: Is there any potential for long term eye damage from LED lighting?

« on: 24/03/2013 12:18:38 »

In general the spectral output from modern "tri-phosphor" fluorescent tubes (and compact fluorescents) has significantly narrower spectral emission-lines than any LED source - so you couldn't argue that LEDs would be worse than FL. That said, I can't see much scope for physcial damage to the eye from this kind of narrow-band spectral light from domestic fittings.

However, all narrowband sources (FL and to a lesser extent LEDs) when used for general lighting, affect "colour rendering" - the way object-colours appear. I think I might be justified in arguing that there is scope for some concern that for an infant developing substantially under such artificial light (with little exposure to natural light) runs some risk of aquiring some kind of subtle developmental disorder in the analysis and recognition of colours - particularly of subtle colour gradations.

19

Technology / Re: Can we generate power from moving crowds?

« on: 14/03/2013 23:58:44 »

But the amount of energy you get out is pretty miniscule compared to the time, effort and energy required to make, install, and maintain any such system. And of course this will make it a little bit more tiresome for the individuals to walk about. There is never any real energy-payback with such systems. "Energy harvesting" is rarely ever really about "energy saving" - it's only real value is when no other source of energy is viable (eg in the middle of nowhere, impractical to have someone changing batteries on a regular basis etc etc).

Wang and his team produced a nanogenerator smaller than a human palm  which generated an instantaneous output power of 1.2 W. While this may not sound like much, it is enough power to light a bank of 600 coloured LEDs with a single human step!

What does "instantaneous" mean in the context of a footstep? Is that a split second each time a foot hits the ground ... a pretty low duty-cycle for walking! Sub 5%? So maybe equivalent to 50mW continuous? Quite possibly less. About 0.02p-worth of (mains) electricity per day from continuous 24h-walking.

20

Technology / Re: What color of headlights is best?

« on: 14/03/2013 23:42:06 »

Bad alignment, causing dazzling to oncoming drivers (or the driver of the car in front) seems to be becoming an every worsening menace where I drive.

If the top-edge of your beam is below the level of the bottom of the rear-window of the car in front, you're probably okay. If it's shining in their rear window then SORT IT OUT!

(I have been tempted to put a passive-aggressive retro-reflective warning sign in my rear-window, visible only to those with too-high lamp alignment ... but haven't got around to it ... yet)