Are light dependent resistors stable wrt time?

Question

This question specifically concerns my issues with an ORP12 like:-

I've read the data sheet and I see that resistance changes wrt short time (15 sec). Also note 1 mentions 16 hours. But what happens after? Is it possible that the resistance could double (69k to 136k) over the course of a couple of weeks? I need this question answering in order to rule out other possibilities for my resistance change in an otherwise steady state system.

There not very precise parts and very temperature sensitive. the repeatability improves with light intensity and lags for a long time in darkness (15s) — Tony Stewart EE75, Mar 07 '17 at 02:55
Repeatability is something like this http://obrazki.elektroda.pl/9650040400_1488855740.jpg maybe as bad as 2:1 in low light — Tony Stewart EE75, Mar 07 '17 at 03:02
If one wants accurate light detection, one uses a silicon PD. — Tony Stewart EE75, Mar 07 '17 at 03:05
See also: http://electronics.stackexchange.com/questions/295969/does-an-ldr-age?noredirect=1#comment680739_295969 In my case I estimate a factor 5 to 10, but over a span of 10 years, not weeks. — jippie, Mar 31 '17 at 21:00
LDR's contain Cd which is on the contamination mineral list. — Tony Stewart EE75, Aug 20 '18 at 15:31

score 2 · Answer 1 · edited Mar 07 '17 at 06:06

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The LDR is not very stable, as has been commented. What does happen over time is that the dark resistance decreases. UV from the sun may be a factor here. You must design your decision circuit to be tolerant of this decreasing dark resistance, otherwise your product will fail at some point in the field. The high sensitivity of the LDR means simple circuits can work. In fact people put them straight into weakly pulled up digital inputs. The decreasing dark resistance issue means that this high sensitivity cannot be utilised in a high reliability commercial product. The old LDRs used cadmium which is not ROHs. New LDRs apparently do not use any cadmium. Both new and old LDRs appear to have this problem.

edited Mar 07 '17 at 06:06

uint128_t

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answered Mar 07 '17 at 03:35

Autistic

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The ORP12 is only lit by a white LED. What happens to dark resistance without any sunlight whatsoever? It couldn't double could it? – Paul Uszak Mar 07 '17 at 11:38
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The dark resistance should be very high ,Say more than 100K and better still 1 meg .The light resistance should be less than 1 K .This huge difference makes setting up a decision circuit easy and allows for degradation in LDR characteristics . – Autistic Mar 07 '17 at 19:57

score 2 · Answer 2 · answered Aug 20 '18 at 14:01

The LDRs in my cheap old solar garden lights got sunburned and failed soon. New solar garden lights don't use LDRs anymore, they use the solar panel to detect light and dark instead.

If sunlight does not destroy an LDR then time will destroy it instead.

Are light dependent resistors stable wrt time?

2 Answers2

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