Arithmetic or Geometric mean?

I used one in a project where it was activated by a one of those laser pointer gadgets in average room ambient light. IOW the ambient light resistance was trimmed out and the laser reliably pushed it deeper into low resistance, and from quite a distance away too.

I'm not sure that would work for lead on exposed rooftops.

I heard it mentioned about lead cargo recovered from Roman ships that sank in the time they still had an empire. It would have been protected from cosmic radiation and nuclear test fall-out by several hundred meters of water, in addition to having had lots of time for its own radioactivity to have decayed.

I did not verify, but I believe it was also used in some of CERN's detectors because of its low background radiation.

Jeroen Belleman

the outside can be can be washed, the contamination left in from the initial melting process has to decay

I think that was mostly for low background steel, steel is recycled again and again so once it has be contaminated with radioactivity in the air from test fallout or radioactive materials used in the process there is no way back

afaict tell it is the cheaper easier mass produced alternative to pure lead. Making steel sheet takes a lot more tools and machines than lead sheet

All the nuclear testing stuff will be on the outside, though. You can get rid of it by an acid wash.

Cheers

Phil Hobbs

ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510

For slow stuff, they have a large response. That's their one claim to fame.

Cheers

Phil Hobbs

There are billions in street lights and such; they only have to tell day from night.

I wonder if more modern controllers use a surface-mount silicon diode. They might be cheaper.

Maybe an LED light can use the LEDs themselves as the detectors.

Yes. I have a design that does just that. In fact, the same LED not only measures the amount of light, it flashes immediately after the measurement and then resumes measuring. The more frequent the flashes, the greater the light level.

Does it have to turn off the light to measure the ambient light level? I think that is going to be objectionable in a street light unless it is short enough to not be visible.

Yes, but it can be used as a light sensor only without flashing the LED. I just wanted something other than a meter or oscilloscope to indicate the approximate light level for testing.

Maybe I'm not following what you said here. Can the LED be used to sense ambient light while the LED in providing illumination?

Sure, it can sense when to turn on the street light, but can it sense when to turn off the street light? How would that work? If you have to turn off the street light to do that, you are probably better off just using a separate element to sense the ambient light.

A couple of microseconds is usually enough.

Cheers

Phil Hobbs

No.

It detects the amount of light it sees. What is done with that information is up to the user. It was not designed to turn on and off a street light.

Even then I wonder if the control to do this monitoring is less costly than the circuit to simply use a separate device to measure illumination. Much ado about nothing as it were.

Yeah, not directly on the idea of using the LEDs in a street lamp to control the turn on and off. It just leaves open the possibility.

terned steel is not limited to roofing. It was simply cleaper than tinned steel as well. You can solder it and it doesn't rust. So it's common for old electronic and electrical equipment as well.

I'm no historian, but I don't think I've ever seen a lead roof in the US. Copper, yes, and you can still have these installed if you're willing to pay for it. They are seamed and soldered.

Copperclad FR4 is cheap on ebay, and is an interesting building material. 2 oz is best.

You could build a house with it.

are they really soldered?,

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