Science Buddies: "Ask an Expert"

i need do this as fast as i can. So please help if anyone knows how to make a solar sensitive cell. plzzzzzzzzzzzzz

Do you have a specific project in mind? You can get ideas from the Science Fair Project Home page.

By solar sensitive cell, did you mean a device that makes electricity from sunlight? If so, would it be OK for you to buy one to experiment with or do you want to actually fabricate such a cell? (That might be difficult.)

Please write back so I can provide more specific help.

Yes, i do have a specific idea in my mind. Everyday we see that street lights are switched on and off at any time. Sometimes it is switched off when it is still dark and switched on when there is light. So my project is to make a working model showing a new way of solving this problem. My idea is that if sunlight sensors are attached to the street lights then in the morning(when there is light) it will go off . I don't want to make electricity out of sunlight. Instead I want to make cells which sense sunlight.
It is also fine if I am able to buy them from anywhere.
However thanks for your time.

tejaswini - This is a power control project, where the power to the light is controlled by the sensed ambient light. A clock timer has the problem of turning on and off at a preset time. As you point out, it can be on during sunlight periods and off during dark periods. There are many commercial or home lights that use a cadmium sulphide cell (CdS cell) to sense ambient light and control the power to the light bulb. The CdS cell is essentially a light sensitive resistor, that changes it's resistance in different light situations. A CdS cell can be obtained at stores like Radio Shack and are quite inexpensive. You will have to do some research on how to create the circuitry to make this happen. I would use a small DC bulb, like a flashlight bulb for the experiment so you can avoid more complex, and dangerous, high voltage AC current. You will probably only need a few inexpensive components like a transistor, a few resistors and such to finish the project.

Rick Marz

thank you rick marz
your idea has helped me a lot
I have a small doubt. Can i use something else in the place of the CdS cell?
and i must be using the DC bulb as the bulb of the street light right?

tejaswini wrote:... Can i use something else in the place of the CdS cell?
and i must be using the DC bulb as the bulb of the street light right?

You sure can, for example something like this
http://www.amazon.com/Velleman-Encapsul ... 614&sr=8-4
will generate 200 mA at 2V from sunlight. That's plenty to run an LED, which only draws roughly 10 mA (depends on color and brightness). However, that lights the LED during the daytime -- just the opposite of the effect you are looking for So the next challenge is to store the energy for night-time use. One way would be to use the solar cells to charge a rechargable NiCad battery during the day, which would then run an LED during the night. But going this route will require some knowledge of basic electronic circuits. We have a primer at
https://www.sciencebuddies.org/science- ... ntro.shtml
You can learn a whole lot more, pretty much all you'll ever need as a scientist unless you want to be an EE, from the classic textbook "The Art of Electronics" by Paul Horowitz. This is expensive so you should borrow it from a local library. Warning: this may be too hard for your grade level. Maybe Rick could suggest a better elementary text?

You'll learn a lot doing this, but learning the electronics and tinkering up the circuits may take quite a while (which, fortunately, you seem to have).

Good luck.

I have another idea in my mind.
What if I could use glow-in-dark substances like zinc sulphide in street light?
They are usually charged by natural light due to which they glow in dark. So it wouldn't use electricity at all.
But the doubt is whether they will be able to produce light as bright as the present electrical street lights.
Please help me.

Alas, I think you are right, zinc sulphide will not be bright enough, nor last long enough for street lighting.

If you want a bright light, a project that might appeal to you would be to use a small 12V battery, for example

http://tinyurl.com/7cj7oj2

(adult supervision needed to add acid to battery when first used) to store the energy from the sun using a solar power motorcycle battery charger (sold many places) and an LED headlight. You would need to build or buy a circuit that would turn on the headlight when it’s dark. I think you could find a suitable combination of charger, battery, and light that would charge for 8-12 hours and shine rather brightly for 8-12 hours. I would guess a cost of about 100 dollars.

You could do the same sort of thing with less cost using a combination of rechargeable flashlight batteries, a bright white LED array, the solar cell I first mentioned or equivalent, plus electronics for voltage conversion, battery charge control, and day/night control. I would guess you’d need some expert help designing and building the electronics, which would take two or three special function chips and a few power control transistors along with an assortment of resistors.

John Dreher wrote:Alas, I think you are right, zinc sulphide will not be bright enough, nor last long enough for street lighting.

yah....Zinc sulphide is not so bright......you can use led light.....it is more bright then zinc sulphide and so longer than other lights.
Led lights

John Dreher wrote:If you want a bright light, a project that might appeal to you would be to use a small 12V battery, for example

http://tinyurl.com/7cj7oj2

(adult supervision needed to add acid to battery when first used) to store the energy from the sun using a solar power motorcycle battery charger (sold many places) and an LED headlight. You would need to build or buy a circuit that would turn on the headlight when it’s dark. I think you could find a suitable combination of charger, battery, and light that would charge for 8-12 hours and shine rather brightly for 8-12 hours. I would guess a cost of about 100 dollars.

You could do the same sort of thing with less cost using a combination of rechargeable led flashlight batteries, a bright white LED array, the solar cell I first mentioned or equivalent, plus electronics for voltage conversion, battery charge control, and day/night control. I would guess you’d need some expert help designing and building the electronics, which would take two or three special function chips and a few power control transistors along with an assortment of resistors.

For more bright light I can suggest you to buy Maglite flashlights because it has powerful battery,warranty and various light effects as well