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measuring light at a distance

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moinkey

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hey guys,

First off let me start saying that i plan to make millions/billions with this design. But its missing a few key components, the first being a device that can measure the light intensity of a wall ~1m away.

Had a quick look and couldnt find what i need, wondering if you guys could help.

Basically i would like to sense light intensity at a certain distance. So i would point my sensor at the wall, and it would return the light intensity. When the light changes on the wall i should be able to detect this. The measured sample area should be small (ie narrow beam) and 50-100cm away.

I know there are devices out there that can measure the light intensity at the sensor, but i need to measure the intensity at the pointed object.

This can be best compared to those Sharp IR distance measurement modules, but i need to measure light intensity at the pointed object instead of distance.

Are there devices out there like this? Or how do i make one?

Thanks in advance for your help

p.s. if i get this going i'll be sure to put it up so everyone can make their own mil.
 
Yes, there are lots of devices like this. You could even use a webcam with fixed (or known) exposure time to get measurements of light intensity.. any light-sensitive sensor with a proper lens will do the job. All diodes are light-sensitive (don't scratch the surface of a regular diode, it can mess up your circuit). Some of them are designed for measuring/detecting light (photodiode, avalanche photodiodes). There are also phototransistors and light-depended-resistors.

Photometer - Wikipedia, the free encyclopedia
Light meter - Wikipedia, the free encyclopedia

What is the intended application of the device?

I have seen a LED matrix that uses the LEDs to measure the ambient light intensity during the off stage of a PWM control cycle. Then the PWM duty is adjusted according to the ambient light. When its dark the LEDs become brighter and vice versa. If you put your hand over the LED surface the LEDs under your hand will brighten up. Very cool effect. Sorry about the off-topic.
 
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It was a very long time ago...I had a camera. Minolta SLR, and it used film! I wanted to find the illumination of the full moon and install lights twice that bright. I learned how to use the camera as a light meter. It worked. I came to the conclusion that devices that measure the light on the subject have been invented. One of them is called a camera with auto exposure.

I hope this confirms your idea.
 
hey guys,

Thanks for your replys. Dx3 - its not so much a proof of concept but its more that i need one. And it needs to be fast (max 20ms) response, thats why i was thinking analog.

MisterT - yes i've heard i can use photo sensitive components and put on a lens, but are there any devices with this configuration already? are there any projects that you know of that have already done this. I just had dicking around with lenses and different components until i get the right combination.

Application - well highly confidential, but essentially i want to check a spot on the wall and when that changes brightness, i need to react IMMEDIATELY (50ms from lighting up to actuator in full force, which gives me about 20ms for detection)

Cheers
 
Buy this one: Phidgets Precision Light Sensor - RobotShop
And this one: **broken link removed**

Replace whatever is inside the webcam with the light sensor. You may have to experiment with the position of the sensor to get good focus.

These could be useful also: **broken link removed**

You could also try a magnifying glass in front of the camera lens to get more narrow angle of view.

One option is to use a parabolic mirror and put the sensor in the focal point of the mirror. You can find parabolic mirrors in flashlights.
http://en.wikipedia.org/wiki/Parabolic_reflector
 
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Most light changes are acompanied by temperature changes. Maybe an IR thermometer (even modified, sensor changed or IR filter removed?)
 
misterT - great answer. thats exactly what im after. So basically rip out a cheap webcam and put a light sensor instead. I like it. will give it a crack.

canadaelk - i think the temp change wouldnt occur at 20ms interval - or would it?

cheers
 
Just a warning that is probably not necessary, Cadmium Sulphide light dependent resistors are too slow for this application.
 
Well call me slow! I did not see that the change to be measured was to be within 20 msec, only that the measurment was to be within 20 msec.
As this is to be a top secret project, I can not wouch for my own confidetiallity!
Cheers, E
 
Hey guy. Had a brainwave. (which is rare)

I could use a video camera with like 30x optical zoom and put my light sensors at the end of those lenses. Gonna rip apart an old camera tomorrow and see what happens,

Cheers
 
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