How to design light intensity measurement cct

[photoelectric]

hi all,

I want to measure the absorbance of light,by using photoresistor and microcontroller(18f4520).reading should be displayed on lcd.can you please help me.

 

[rezer]

Wow, that's a really open-ended question. Help with what? Do you want to know how the photo-resistor works? How to interface it? How to convert the resistance to an actual measurement? For a project like this, with no specific question(s), you must be a bit more precise on what you are asking.

 

[Torben]

Wow, that's a really open-ended question. Help with what? Do you want to know how the photo-resistor works? How to interface it? How to convert the resistance to an actual measurement? For a project like this, with no specific question(s), you must be a bit more precise on what you are asking.

Agreed.

Photoelectric, do you have any schematics or diagrams of your setup that you could post?

Are you trying to detect the absorbency of different materials? Meaning for instance, if you bounce the light off of polished steel you'd get a very low absorbency reading, but black felt would give a much higher reading?

What are the units in which you must display the results? e.g. weight would be in grams or kilograms or so; light maybe in lumens; what units would absorbency be measured with?


Torben

 

[ericgibbs]

hi,
Also what visible light frequency.?

When you say absorbancy, do you mean light transmission attenuation thru a sample.

Or reflectivity of a surface.?

The read out would be, I guess a percentage of 100%.

Morning Torben.

 

[Torben]

hi,
Also what visible light frequency.?

When you say absorbancy, do you mean light transmission attenuation thru a sample.

Or reflectivity of a surface.?

The read out would be, I guess a percentage of 100%.

Morning Torben.

Morning Eric!

Good points. I would choose a percentage as well, but I wonder whether there is actually a unit of absorbency other than percent which must be used here. I suppose I could google it.


Torben

 

[ericgibbs]

hi,
Found this absorbance pdf.

 

[Torben]

hi,
Found this absorbance pdf.

That is interesting reading. So there is an absorbance unit: Au. Neat.

That article seems to deal mostly with transmitted light, not reflected. That's also something to think about. I guess we still don't know what the OP's requirement is.


Torben

 

[jpanhalt]

That is interesting reading. So there is an absorbance unit: Au. Neat.

Torben

Saw the reference. The usual way to express light absorption for application of the Beer-Lambert law is by optical density (OD):

OD = log(Io/I)

where Io is the incident beam intensity, and I is the transmitted beam intensity. Thus, something that transmits 10% of the incident beam (absorbs 90%) has an OD of 1.0. Obviously, the equation as written is mathematically identical. I simply find the ratio easier to remember.

There is a small typo in the reference. The equation given is: A = 2 - log(T).

That should be A = 2-log(%T).

Reflected light can be dealt with the same way, but I have usually seen such values shown as percentages, not as logs.

BTW, remember all of this refers to monochromatic light. The ratio of total incident and transmitted light intensities for polychromatic light will not follow Beer-Lambert.

John

Edit: The concentration dependence predicted by Beer-Lambert doesn't apply to reflected light, so far as I know. I did not mean to give the impression that it did. By polychromatic, I mean many wavelengths. One can construction situations in which the law is followed with multiple wavelengths and even with mixtures of compounds, but those are outside the scope here.

 

[photoelectric]

Wow, that's a really open-ended question. Help with what? Do you want to know how the photo-resistor works? How to interface it? How to convert the resistance to an actual measurement? For a project like this, with no specific question(s), you must be a bit more precise on what you are asking.

thx for replying...

Well, the idea is to design the cct that measure the light intenstiy(brightness or sumthing...) in different room...
.just like measuring temperature in different room...any idea to start?...any cct u all can suggest?...display must
be on lcd..im using micro-controller INTEL 8085 to programme the cct...

tq

 

[photoelectric]

Agreed.

Photoelectric, do you have any schematics or diagrams of your setup that you could post?

Are you trying to detect the absorbency of different materials? Meaning for instance, if you bounce the light off of polished steel you'd get a very low absorbency reading, but black felt would give a much higher reading?

What are the units in which you must display the results? e.g. weight would be in grams or kilograms or so; light maybe in lumens; what units would absorbency be measured with?


Torben

hi Torben,

sry for the lack of infomation.Yeah,im trying to detect the absorbency of different material...absorbence (Au) and the concentration in different pigment..can i use Phototransistor (OP593B) or LDR - VT935G
or BPW34 Photodiode and using 8-bit ADC ...display should be in lcd...?
u have any idea or shematic diagram?

 

[jpanhalt]

hi Torben,

sry for the lack of infomation.Yeah,im trying to detect the absorbency of different material...absorbence (Au) and the concentration in different pigment..can i use Phototransistor (OP593B) or LDR - VT935G
or BPW34 Photodiode and using 8-bit ADC ...display should be in lcd...?
u have any idea or shematic diagram?

That description is very confusing. Absorbance in this context refers to solutions. That is, the substance has to be dissolved. Dyes dissolve; pigments generally do not. The term "concentration" refers to solutions in this context. Non-solutions are mixtures and generally are described by percentages.

1) So, are you trying to measure absorption of light by a solution or reflection/scatter from a dispersed solid?

2) Are you trying to apply Beer's law to estimate concentration? If so, you need monochromatic light.

John

 

[photoelectric]

That description is very confusing. Absorbance in this context refers to solutions. That is, the substance has to be dissolved. Dyes dissolve; pigments generally do not. The term "concentration" refers to solutions in this context. Non-solutions are mixtures and generally are described by percentages.

1) So, are you trying to measure absorption of light by a solution or reflection/scatter from a dispersed solid?

2) Are you trying to apply Beer's law to estimate concentration? If so, you need monochromatic light.

John

hi John,
sry for the idiot explaination...forget about what i say before..im trying to design a cct that measure light intensity using BPW34 Photodiode,Phototransistor (OP593B) or LDR - VT935G.but im not sure which or what intensity is,maybe in term of brightness or sumthing...measuring absorption of light seem complicated to me but what about voltages or current?...can we do that?using the above device,can i actually measuring voltages and current with differnt light intensity...eg.dark room show zero voltage??...

 

[moonlit]

Hi folks, Even i m sailing the same boat as Photoelectric, if anyone has ideas on the topic kindly throw somelight on it.

 

[Rolf]

Light Meter .....

hi John,
sry for the idiot explaination...forget about what i say before..im trying to design a cct that measure light intensity using BPW34 Photodiode,Phototransistor (OP593B) or LDR - VT935G.but im not sure which or what intensity is,maybe in term of brightness or sumthing...measuring absorption of light seem complicated to me but what about voltages or current?...can we do that?using the above device,can i actually measuring voltages and current with differnt light intensity...eg.dark room show zero voltage??...

Sounds like you need a light meter similar to what photographers used in years past.

Here is a link that might be of some help:

https://www.electro-tech-online.com/custompdfs/2009/01/Build_Your_Own_Light_Meter-1.pdf

 

[photoelectric]

Hi,

FYI, i already complete doing this project for my semester.
The objective of this project is to measure the light intensity in terms of voltage.
Im using photoresistor as component to convert physical qty aka light intensity.
Then,using basic Wheatstone bridges and amplifier to control the voltage output to maximum 5V.
Measurement then display with µC based processor.
Actually,this project use simple concept.

Thanks,

 

[brenda]

Hi,

FYI, i already complete doing this project for my semester.
The objective of this project is to measure the light intensity in terms of voltage.
Im using photoresistor as component to convert physical qty aka light intensity.
Then,using basic Wheatstone bridges and amplifier to control the voltage output to maximum 5V.
Measurement then display with µC based processor.
Actually,this project use simple concept.

Thanks,

Hey photoelectric,

Do you have a schematic diagram or something regarding this topic? I'm trying to build the exact same thing.

 

[photoelectric]

Hi brenda,

i will be closing this thread soon. So u can email me at paansmat@yahoo.com for more information about this project.

Unfortunately, my laptop now have a serius problem and need to be repaired.
All data about the project in that laptop.
So, i cant guaranteed u about the schematic diagram of the project now.

Thanks,
Photoelectric

 

[brenda]

Hey Photoelectric, I'm still struggling with this project at the moment. Would really appreciates it if you can email me with the schematic an such. My email brenda.bb7@gmail.com. Thank you.

 

[Ubergeek63]

as i recall photocells are not particularly stable or accurate.

https://www.electro-tech-online.com/custompdfs/2009/03/TSL237T.pdf is a decent light to frequency converter that Future sells for $3.60 in singles. There is also a side view TSL237S.

Dan