Light Sensor

We are using a T-18 photo-resistor (NSL 19M51), it has a good range (100K to 1M) for ambient light. They typically use these for night-lights. For more accurate reading, adjust the reading with a temperature sensor such as the NCP18WF104 themistor.

Thanks. How do these things respond to heat? it's going to be next to a heat source that will be going up and down. There isn't any data available on their website.

We were testing them on a 40C for 8 days constant temperature chamber.

We did ramp it up to 80C for stress testing, no damage at all.

From a recent newsbit on the Avnet distributor site:

Try a common led!

I need something that will receive light rather than transmit light. An LED is a Light EMITTING Diode.

LED's supposedly will produce a photocurrent, though I've never personally this. Another option is a photodiode, there are cheap ones available from Digikey: part # PDB-C113 is under $2. It's in a ceramic package, so I imagine it's heat tolerance is quite good.

Mark

Whoops, should have said: ... I've never personally tried to measure this.

Mark

This "cheap" photodiode is only $8.16 from Digikey. The NSL-19M51 is listed for $0.44 from Allied-Electronics, but I guess there is a minimum buy. We only have a couple of samples (taken out of $2 night lights), will let you know when we are ready to order more.

A photoresistor also has better linear brightness response, in case you want to know more than just black and white.

No kidding! Just *try* it. You might see more than one volt in a high impedance.

A year ago the price was $1.65. Damn.

Mark

I might have missed something here , but what is wrong with a simple LDR? Rob

An LDR is just a photoresistor right? I'm not up on the terminology yet. I really just need to know if it's dark or not dark. I'm not too interested in any linear responses to light. Thank you all for your help so far. Good stuff for a freshly minted EE grad.

Practicality Sir. If your junkbox is anything like the average electro-tinkerer's junkbox - there are several led's there. Or some old PCB from whence they can be harvested. Stick an opamp behind it, and behold a perfect light sensor.

An LDR on the other hand, is less likely to reside in aforementioned box. I may be wrong though - in which case use the appropriate part as deemed adequate.