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Light-activated lamp, cries out "Me too!" when other lights are turned on Answered

Disclaimer: I have little-to-no electrical experience, but want to use this rather involved project as a starting point to hone my abilities and technical know-how. Any non-basic terms I use are based purely on assumed naming schemes. I only have fuzzy notions of what things like photovoltaic cells or flux capacitors are, but I'll write as if I know them perfectly, just in case I'm actually using the terms properly. If this post starts a thread that can answer all aspects of how to get this done, I'll update it as an instructable for others to learn.


I'm looking for some guidance. I have a plan to modify one of my lamps to brighten and dim based on the amount of light hitting it: Essentially, if I turn on a larger light, this lamp will turn on as well. As this is still simply an idea in my head, though, I plan to make it rather complicated and feature-rich.


Two main settings for the light: Absolute and Relative.

When in Absolute mode, the lamp will turn on and off based whether or not the amount of light hitting its photosensor surpasses the necessary threshold energy level (TEL). The TEL will be adjustable by the use of a small dial, so that as the TEL approaches 0, the lamp turns on regardless of any additional light, and as the TEL approaches Infinity (or, at least, the maximum amount of light the photosensor can detect), the lamp turns off. Of course, I'd plan on primarily keeping the TEL at the level at which the lamp only turns on when I've turned on another light in the room, but there are times when I'd want the lamp to be independent of other lighting.

When in Relative mode, the light would brighten and dim based on the relative amount of light hitting its photosensor, so that the more lights I have on around it, the brighter it gets. I'd like to be able to use the same dial from Absolute mode to calibrate the relative brightness of the lamp, but that may be overly complicated for the amount of benefit it provides. Additionally, it would be interesting to invert this relationship, so that as less light hits the photosensor, the brighter the lamp gets.

A next step could be to layer the exterior of the lamp with solar cells so that it can not only activate based on its environment, but actually power itself (at least partially) based on its environment. This is not as important as any other features.


I plan on developing this post with a diagramed model of how this would work, but first I'd like to iron out a few issues:

-How does a photosensor detecting light export information?
-Assuming the photosensor exports electricity, what does the sensor need to be hooked up to in order to become meaningful?
-How would I set TELs, and how could I set TELs with a controllable dial?
-How would I swap between Relative and Absolute modes? How could I add a switch in to do this easily?
-How would the lamp's own light effect the photosensor if the photosensor was positioned on an opaque lampshade?
-Has anyone else done this, or something similar, so that I could look to those projects as a model?
-What else do I need to know?

I'm not specifically asking for someone to answer every question for me, but I would greatly appreciate it if I could be pointed in the right direction towards resources that would help me figure out the technical aspects of this project. With the small amount of experience I have, I'd expect to have to do a lot of reading.

Thanks for any responses!


Anyone else thinking OP-AMP comparator?

me too the same op amp can be used for both modes. in hte relative mode it has negative feedback so it really works like amp and not comparator iirc some audio amps (like tda2002) are power opamps

I wasn't, but now I'll be researching them! Thanks!


9 years ago

As has been noted, there are several avenues you can explore on this one--I like the analog approach, since you won't need to program any uCs.

Here's a link to get you started: analog light dimmer circuits. Look specifically at the "Simple voltage controlled dimmer," which uses an LDR (light dependent resistor) to control the output. Cadmium sulfide (CdS) photo resistors are cheap and easy to find...

How you place the CdS cell, together with a resistor or two (a voltage divider) will determine the sensitivity and the "direction" (brightness + or - relative to ambient light.) Some additional (but simple) circuitry would be required to make the lamp turn off when brightness reaches it max.

What a great posting! You have a terrific idea (it may have been done before, but it is still your idea), and you are well on your way to achieving it. NachoMahma has given you some good, detailed guidance for the specific questions you asked.

I second his recommendation that you read some of the I'bles (or other resources on the Web) for "how to solder," "basic electronics," "microcontrollers" (if you really want to go that route).

In principle, you should be able to do this project with just two components: a small solar/photovoltaic cell and and a normally open relay might be enough: the solar cell would generate a small voltage/current to trigger the relay, turning on the lamp. When the external light goes away, the solar cell turns off and the relay opens.

. The only real issue I see is the sensor seeing the light it is controlling and getting unwanted feedback. . Using the same pot for different functions in different modes is just wiring up a multi-pole switch. You'll need the switch to change modes, just get one with enough poles/contacts. . . Some detectors are variable resistors, some are transistors. Probably other types. Which is best depends partly on the application, but a lot depends on what you have in your junk box. You can buy a black box with just about any type of output, but they all use the same few detectors. . A photo-resistor does not require power to do its' thing, but you have to pass current through it to measure the resistance. Transistors require some source of power to operate. . Your idea of using a pot is probably your best bet. If you use whatsisface's comparator idea, you will probably be adjusting the gain of an op-amp. . If you have only two modes, a slide switch will work well. For more modes, a rotary switch might be a better choice. . There's the rub. It shouldn't be an insurmountable problem, but you may have to do some experimenting. . I haven't, but I bet someone has. Probably more than one person uses a microprocessor (eg, Arduino). Try searching for something like "programmable light dimmer", "adjustable light dimmer", &c.; Appending "+DIY" or "+schematic" should help narrow things down if you get too much trash. Try replacing "dimmer" with "controller". . A lot, but you're on the right track. While you're waiting for other answers might be a good time to check out the iBles on soldering, op-amps, microcontrollers (uC), &c;.

"Light-activated lamp, cries out "Me too!" when other lights are turned on" Well for a start you would quadruple your audience, by making the lamp cry out "Me too!" when the other lights are turned off. In this NEW Green world little reminders like that ,would be greatly appreciated.

Yup, that's exactly the functionality I'm looking for – this lamp would be subordinate to any other lighting in the room, thus would deactivate as soon as any other lights are turned off. Sunlight is a non-issue in this space, but, as that won't necessarily be the case for everyone, I'm going to see if I can't find some way around that as well. It'd be pretty impractical if the lamp turned itself on in the daytime when no-one's around.