Hey people,
i want to mesure the amount of lumen with a ldr. I also have a 10k resistor. How can i transfrer the data from analgRead(); to the amount of lumen?
note: lux is often confused with lumen, but lux is amount of lumen per square
Great thanks if you have an answer for me! (link or propper code would be nice)
LDRs are highly nonlinear and not particularly useful for measuring light intensity. Most people use photodiodes instead, because short circuit current of a photodiode is directly proportional to intensity over an extremely wide range of values.
You will have to calibrate any device you build against a commercial instrument.
Thats to bad to hear. So what kind of purpose do ldrs have then?
LDRs are used to detect changes in light intensity, absolute intensity (e.g. as a precalibrated light level switch), or in pairs, to compare relative light levels.
Why is the suggestion of using the proper tool for the job "too bad to hear"?
Try BH1750 instead of LDR.
Good idea to use a BH1750 module! Circuit example here.
Keep in mind that the BH1750 can't handle full, direct sunlight at noon (~120,000 lux).
Ryan_pi_programmer:
Thats to bad to hear. So what kind of purpose do ldrs have then?
Not many these days, but amplitude feedback in the lowest distortion audio oscillators is one niche area.
LDRs typically have long time constants compared to other opto devices, sometimes this averaging
effect is useful (ie averaging out flicker from artificial lights directly in hardware, so an exposure meter
for photography might naturally use an LDR)
Also LDRs contain highly toxic cadmium so are usually avoided in consumer electronics.
Photodiodes are general much more precise, temperature independent and higher speed and cheaper.
"Photodiodes are general much more precise, temperature independent and higher speed and cheaper." I think they are also more reliable.
LMI1:
"Photodiodes are general much more precise, temperature independent and higher speed and cheaper." I think they are also more reliable.
I don't think so. Generally, semiconductors junction devices are vulnerable to static electricity, overvoltage, EMI, X-ray/ gamma radiation. LDR has no problem with that.
Thanks for the replies,
@jremmington: i only have ldr's, i'm quite a cheap skate so i want to use what i already have.
@FantomT, thanks for the tip! Shall consider it, but it's not urgent for my project
Ryan_pi_programmer:
i only have ldr's, i'm quite a cheap skate so i want to use what i already have.
The neighbours might have some solar lights in the garden.
The solar cell, with a burden resistor across, makes a good light meter.
Leo..
this link says is to buy a light meter with a ldr attachted to it.
LDRs are highly nonlinear and not particularly useful for measuring light intensity. Most people use photodiodes instead, because short circuit current of a photodiode is directly proportional to intensity over an extremely wide range of values.
That board in the link is a joke.
LDR with 10k pull down resistor, and a useless 1x buffer opamp (LM358).
Don't expect any linearity from an LDR/resistor (for lumen measurements).
They are only ok as light detector, e.g. for a night light.
Leo..
i'm quite a cheap skate so i want to use what i already have.
Fine! It will be an excellent learning experience.
Follow this article to make a very crude luxmeter using the junk you have on hand. You will have to figure out some way to calibrate it.
I think there are ICs made for measuring illumination, luxes or whatever.
FantomT:
I don't think so. Generally, semiconductors junction devices are vulnerable to static electricity, overvoltage, EMI, X-ray/ gamma radiation. LDR has no problem with that.
But an LDR is a semiconductor device too... And semiconductor junctions are not very vulnerable to
static, you are confusing them with MOSFETs, where the gate oxide layer is extremely vulnerable to static.
Any piece of intrinsic semiconductor will act as an LDR (and also a temperature dependent resistor), since
photons and heat both create electron-hole pairs.
Oh thanks people,
I'm going to check out the link and reply if anything works 
It doesn't have to be a preciese lumen meter (judging from you guys and girls), so i rewrite the purpose to a light detector