I said one of the maintenance person of Carmel hospital, that they must return the photocells that controlled all Carmel hospital outdoor lighting in the past, that they replaced with timer switches, because of the increased maintenance that a timer switch requires over a photocell (Timer switches need adjusting every month compared to photocell which don't needs adjusting).
Initially, the maintenance persion asked me which device can handle higher currents: A photocell or a timer switch (At least what I remembers. He thinks that a timer switch can handle higher currents than a photocell). Then I said him that this is irrelevant, and that all of the streetlighting Maalot Tarshiha operates with photocells, and then he thought that each lantern have PC on it (Like how streetlighting in North America, UK and Australia works), then I've said it that the PCs controls large groups of lanterns like the timer switchs of Kiryat Ata streetlighting, and the remote controlled streetlighting controllers of Nesher and Haifa.
Then he began to say that a timer switch last much longer than a photocell which usually fails after 1 year average. Then I said him that there were local made thermal-mechanical photocells that lasted for decades, and I argued with him.
Your opinions please.

Does the technician have an electrical license or some form of qualification to back his knowledge if not then what he thinks and says is irrelevant...Simple. From my some experience as a maintenance tech for building most of them do not have license nor do they have qualifications relevant to the field so they are basically working off observing past experience alone or worse follow what others have done.

Your tendency to argue people into converting systems from solution A to solution B to your liking this second competes with that of the greenies arguing to convert working T8 to LED....

AAAND you both came out wrong :

1. My gallery is not a manufacturers catalog. The thermal photocell you found there is near 20 years old and you cannot take for granted that they are still made (last time i seen any like that in the shops was 10 years ago)

2. Said photocell was made in Japan

3. There may be some problem which you are not aware of, and prevents the possibility to use the same switching scheme as used in a city. For example just off the top of my head, some late addition remote gate opener etc may be tapped into existing underground lighting grid (with tat being the only nearby power available), requiring the grid to be powered on all the time and this way requiring each lighting device to be switched on its own...

4. Out of few facts and far between (the thermal photocell's existence, the city switching scheme and so on), you managed to assume a lot more things which might or might not be correct. This is one possible outcome of taking things out of their context, but not only of that. Not limited to LG (where i was the "quoted source" far too many times) or discussions with electricians you meet, or much worse, users on HWzone who ask for small consultation related to a light in their home and get a page of LED bashing with links to LG in return..... Please be very carefull when handling information

5. If the "current carrying capacity" came into your discussion this suggests that they might have abused the photocells at above their current rating, or with inappropriate load type. This in turn results in melted plastics, welded contacts, blown triacs and whatnot - more often than not in form of "random failures" after a while and not all blowing up in the 1st night. No surprise they dont like photocells..... (and if you wonder, i seen my fair share of time switches stuck in "on" due to welded contacts as well)

6. It is not possible to conclude about "all photocells" vs "all time switches". In each group there are the few rated for 3A and for 16A, few capable to handle arcing from PFC capacitors and few not, few made for 20-30-50 years and few made for exactly the time it takes to leave "5*" on the seller's rating in Ebay. It makes no sense to compare them

Both? Why am I implicated? I had no idea the argument was with you Ash? Please! I have no intention of arguing I already had vulgarities hurled at me on Youtube.

Both = Dor and the electrician of Carmel hospital

Ok...

Back to the question:
First assume none of them is overloaded. That expectation is not limited to only the steady current, but cover the turn ON and OFF surges as well. So really talking about life expectations and random failures.

The timer switch have indeed many ingredients to work reliably over way longer time: It could be completely covered, so well protected against elements. So what remains are the intrinsic failures. But the simple electromechanical timers are so simple, these could be virtually nonexistent (well, except welded contacts as a result of an overload, but I do not count these here).
But such simple timer need regular readjustment, as it is not able to hold the correct time for too long.

On the other hand the photocell sense the light level, so it does not need any readjustment at all. But because it have to sense the environment, it can not be made so well protected as the timer switch could. So it is more or less exposed to elements.
From all the elements the most problematic are heat and light.
The CdS sensor is known to degrade over time when exposed to strong light, while as any degradation, it is accelerated by the high temperature.
Now this mean a physical limitation on the photo switch life: After some time the CdS element degrade so, the switch stop working.
How long it take depend on few factors:
- How much degradation the switch design could tolerate. When the design remain operational with way more degraded element, it mean it will take longer time for the sensor to degrade to such level, so the lifetime would be longer. But the acceptable degradation level is directly linked to the required accuracy: More accurate threshold requirements mean less room for sensor degradation and vice versa. So installing the sensor on really a dark (during the night) place mean the sensor could be set to lower lighting levels and as it degrade and the threshold light level increase, it still remain good enough for the task.
- How fast the CdS degrade, so mainly to how much light it is exposed during it's life and on what temperatures.
This strongly depend on how it is installed: The CdS should never be exposed to direct sunlight (that's, why the US NEMA photocells have the "Nord" arrow - when the CdS inside a dark box faces Nord on the North hemisphere, it could never be exposed to direct sunlight, as the sun never shine from the Nord). Not observing this instrallation rule mean the life would be short.
Other aspect is the heat: The simple electromechanical photocells (the CdS control the current into either electromagnetic or thermal relay) dissipate quite a lot of power on the CdS itself, what mean it run warm. And this heat then speed up it's degradation. But these photocells are simple, so otherwise suffer less failures.
On the other hand the electronic photocells could use other, less sensitive, but more durable light sensor elements, so they do not suffer from the sensor degradation. But because they are more complex, the random failures would be way more frequent.

So to sum up:
- The timer switch could last longer, but need about monthly readjustments.
- The photo switch could last only a year (when it is subjected to stray light, so it's threshold have to be kept precise), but need no readjustment. But the year lifetime mean it should be replaced each year.
So what option is better? Well, in all professional environment it is the way of lower total cost:
Photo swithc have to be replaced each year, so you need to buy new one each year. But you have to go there to fix it only once a year.
The timer last for let's say 10 years, but you need to go there 12x each year to readjust it.
So what is very strong factor here is the cost to go there: Somewhere it is just where the technician is going around regularly anyway, so the monthly readjustment is nearly for free. So there the timer switch would win.
On other places the service man have to travel there, frequently with a bucket truck. But one voyage of such bucket truck (fuel, truck amortization, driver pay) use to cost many times more than new photo switch, so there buying a new photo switch each year could be the way cheaper alternative, as you have to pay the travel only once per year (and not 12x as with the timer adjustments). So even when the photo switch last way shorter, it could become the cheaper option there.

So you see, than there is no single correct answer to what to use there, there are always many aspects to consider...

One more thing about time switches. Most electronic time switches (and this includes a few with dial, just the driver inside is based on ELV circuit withquartz and not on the AC) contain a battery for backup to keepthe time during outages. This battery impose 2 limits on the device life

1 The timer will not keep the time during power outages after battery EOL

2 Few years later the battery may also start leaking and destroy the circuit completely

I'd expect this to happen on the order of 20 years. But the lifetime of a good CdS "passive" photocell is on the order of to 20-30 years as well

And i think if eithr would last them 20 years they would not complain like that.... So what happened was by far not normal EOL of normal uality device

Quite usual cause of premature PC degradation is the wrong mounting position - when the sun shine directly into the CdS. Mainly the direct relay drive ones are sensitive to this - given by the voltage and thermal loading of the CdS...

And whatever electronic (both timer switches, as well as the photocontrols) are suffering from the problems of an electronic on long wires outdoors (so exposed to induction from thunderstorms,...)

And regarding the overloads, quite frequent source of problems are triac (so not relay) switching mainly the capacitors (PFC ones; the classic CWA ballast does not pose such problem, but virtually all electronic do). Some triacs have problems with switching an inductive load too, but that could be quite well treated by connecting a VDR parallel to the triac.

But the triacs have another severe problems: They sometimes tend to fail so, they become conductive in one direction. For incandescent lamps this is usually not as big problem, but for anything magnetic this is killing. And it quite reliably destroy the "impedance protected" small fans as well - the "impedance protection" is only a leakage inductance, what prevent the current from rising when the rotor is blocked, so the motor survive that for very long time. But when there is a rectifier in series with the fan (= the damaged triac), the current may rise way higher the thing is designed for and usually after about a hour the motor fail (usually the thermal fuse trip)...