Discerning LED white light from natural sunlight?

[MC1992]

Hello, I'm sorry if I didn't word the title better.

 

Summary: I'm trying to detect sunlight while the LED luminaires are present and turned on.

 

I know it may sound kind of strange but this is the idea: say you have a lounge. The LED ceiling light is on, and at the same time, natural light is coming from outside through the window. And the natural sunlight is sufficient, thus the LED lighting clearly is a waste of energy and one more reason to increase carbon emission.

 

But often times people are too busy with themselves to care about this. You just finished an important meeting and are thinking about something really stressful, no one would notice the light is on, esp. when the room is already fully lit by natural sunlight.

 

Now imagine 100 office buildings with 1000 such lounges over a year, the waste could be significant.

 

So is it possible to detect certain section of the spectrum of natural sunlight, the section where it is strongly correlated with sunlight, but almost non-existent in the lights emitted by WHITE LEDs?

 

I know most people probably would immediately think of infrared, problem is, this may not be the easiest direction since there may be extra heat source in the room, for example, a boiling coffee pot or a freezer.

 

Also I wish the solution could be relatively affordable, so I'm guess I may have to stick with infrared/ultraviolet, however difficult. Because anything beyond is either exponentially more difficult to detect or simply too pricey.

 

Last but not least, you can not temporarily turn off the LEDs themselves, it'll take another thread to explain why that is not an option, so I'll just simply put it here: that is not a viable solution, due to some reasons.

[Klaynos]

Different types of white LEDs have different spectra.

 

If you have a given type of led you could measure at a single frequency which is low intensity (last time I looked most white LEDs are quite spikey in their spectrum) and wait for it to increase. This won't be universal though.

 

A better option is a photodiode in a shielded case you place against the window. You can then measure the light entering from outside.

 

UV is unlikely to work as glass tends to be a good UV absorber.

[mistermack]

Wouldn't it be more simple to just monitor the overall light level in the room?

Does it matter if it's sunlight or LED, if the light level falls below a certain point, the LEDs come on.

 

Just like a thermostat on the heating. It doesn't matter where the heat is coming from, it's the temperature that's important.

[Klaynos]

Wouldn't it be more simple to just monitor the overall light level in the room?

Does it matter if it's sunlight or LED, if the light level falls below a certain point, the LEDs come on.

 

Just like a thermostat on the heating. It doesn't matter where the heat is coming from, it's the temperature that's important.

You need to be careful with sensor placement. But yes.

[Tim88]

To add to mistermack's reply: usually daylight is relatively strong, and people are only interested to switch off the LED light when the room is well lit by the Sun.

It may be good enough to detect on the outside of the LED lamp, with the sensor area on the outside, if the environmental light strength is above a certain threshold.

[koti]

It is possible but I dont think it makes sense both financially and practically in your particular case. In order to measure distinct temperatures of light you would need a spectrometer. These are widely used for calibrating monitors and printers. As opposed to a luxmeter (these are used in photo shoots for example) a spectrometer (spectrophotometer) is capable of not only measuring intensity of light but also its color temperature. You can get a chepo spectrometer for calibrationg your monitor for around 600 USD. In order to accuratly measure distinct tints/colors of light in different areas in a big room you would need to spend tens of thousands of dollars for a system. As for the LED's, its a constant chase after the ideal tint/bin type of the emitter to represent natural sunlight. The "Nitchia" company manufactures 90+ Cri LED emitters which are widely considered as best in representing natural light, they are nowhere near as bright as the "Cree" emitters like the XH-P 70 which can be used in street lights for example. What mistermack wrote above is probably your best direction, this light/intensity/color stuff gets really complex and nasty once you digg deep into it.

Edited March 15, 2017 by koti

[swansont]

It is possible but I dont think it makes sense both financially and practically in your particular case. In order to measure distinct temperatures of light you would need a spectrometer. These are widely used for calibrating monitors and printers. As opposed to a luxmeter (these are used in photo shoots for example) a spectrometer (spectrophotometer) is capable of not only measuring intensity of light but also its color temperature. You can get a chepo spectrometer for calibrationg your monitor for around 600 USD. In order to accuratly measure distinct tints/colors of light in different areas in a big room you would need to spend tens of thousands of dollars for a system. As for the LED's, its a constant chase after the ideal tint/bin type of the emitter to represent natural sunlight. The "Nitchia" company manufactures 90+ Cri LED emitters which are widely considered as best in representing natural light, they are nowhere near as bright as the "Cree" emitters like the XH-P 70 which can be used in street lights for example. What mistermack wrote above is probably your best direction, this light/intensity/color stuff gets really complex and nasty once you digg deep into it.

 

 

Alternately if there was one part of the spectrum that had distinct-enough characteristics, you could use a bandpass filter and photodiode. But monitoring the overall light level is an easier and more direct solution to the problem.

[John Cuthber]

LED lights typically have a "notch" in the spectrum between the blue/violet and the green.
Like the one here

http://electronics.stackexchange.com/questions/124095/how-to-generate-red-light-from-a-blue-dominated-spectrum

 

So, if you had two light sensors with narrow filters and measured the brightness at, say 450 and 510 nm you could tell if the light was from an LED.

However the suggestion from Mistermack is a lot easier and better.

Edited March 15, 2017 by John Cuthber

[imatfaal]

The overall measure of light intensity was an option when I refitted my offices - to be honest we went for motion sensing with over-ride insteadd - but our prefered choice was a mixture of light intensity and motion; but we could not get both options merged together (ie turns on light if there is someone in the roon AND room is dark). We made a saving of around 40% on our electricty as it was - so an even more refined system would be fantastic.

[John Cuthber]

The overall measure of light intensity was an option when I refitted my offices - to be honest we went for motion sensing with over-ride instead - ...

Glad you got an over-ride

 

http://dilbert.com/strip/1995-02-22

[imatfaal]

Glad you got an over-ride

 

http://dilbert.com/strip/1995-02-22

 

Gotta love cubicles

 

The over-rides are the best bit - little hand-held thingies; after a few days of turning other peoples lights off everybody tended to use natural light for whatever portion of the day allowed it and control their lights manually. People will not get up and turn off a light - but with a remote they do it regularly

[Phi for All]

Apologies if this has already been mentioned, but aren't we talking about daylight harvesting? The controls for that are available now, and they're awesome. Lutron makes some commercial models that will dim on bright days and boost the light on cloudy days.

[imatfaal]

Apologies if this has already been mentioned, but aren't we talking about daylight harvesting? The controls for that are available now, and they're awesome. Lutron makes some commercial models that will dim on bright days and boost the light on cloudy days.

 

I was talking about that - not sure it wasn't a bit of a branch.

 

At my offices we couldn't use a dimmer system as the fluorescents we use don't do dimming. Not sure if LEDs do either - but with LEDs you could, I guess, turn on a limited number of the array

[Phi for All]

 

I was talking about that - not sure it wasn't a bit of a branch.

 

At my offices we couldn't use a dimmer system as the fluorescents we use don't do dimming. Not sure if LEDs do either - but with LEDs you could, I guess, turn on a limited number of the array

 

The diodes are all capable of dimming (yay, solid state!). With LEDs it depends on the driver used. If the driver (which replaces the ballast fluorescents use) is dimmable, the luminaire is dimmable. Daylight harvesting is mostly effective for the lights that are closest to windows. Further into the building, the need for light is pretty constant, so dimming isn't necessary.

[MC1992]

Different types of white LEDs have different spectra.

 

If you have a given type of led you could measure at a single frequency which is low intensity (last time I looked most white LEDs are quite spikey in their spectrum) and wait for it to increase. This won't be universal though.

 

A better option is a photodiode in a shielded case you place against the window. You can then measure the light entering from outside.

 

UV is unlikely to work as glass tends to be a good UV absorber.

 

Thank you very much for your input. What you mentioned is a legit problem, because we haven't decided which type of LED/LEDs we will be using, the logistics and sourcing can be a tricky business, I'm looking for the general direction at this ponit.

[imatfaal]

One point - if you are looking to place a sensor then it should not be on the window measuring natural light coming in, it should be on the desk or maybe on the top of the monitor to measure total light arriving at work station.

 

A double sensor of total light and an LED specific band would allow simple troubleshooting and monitoring

[Bender]

On dimming of LEDs: they don't usually dim, because they operate at a much lower voltage, and therefore contain electronics to convert any input to the supply they need (there have been problems with LED lights being on even with the switch turned off, because of a small voltage caused by capacitive coupling between the wires).

 

Dimmable LEDs contain additional electronics to implement e.g. PWM based on the input they receive, which is quite similar to how a traditional dimmer works.

Edited March 16, 2017 by Bender

[mistermack]

You need to be careful when buying dimmable systems.

If the objective is to save energy, you may be wasting your time on dimmable ones, because the electronics involved in dimming them might be just dumping the extra energy as heat.

I have a couple of LED torches that work on batteries.

One is dimmable and the other is not. They both have the same Cree T6 LED and both are very good and bright.

But the dimmable one gets warm, even when dimmed, and the battery actually doesn't last as well as the non-dimmable one, even if it's on the lowest brightness setting.

Clearly, the reason that it gets warm in the hand is because the electronics are dumping some power as heat, in order to make the thing dimmable.

 

It doesn't really affect the use of it, but it's ironic that the non-dimmable one on full power lasts longer on it's battery, than the other on the dimmest setting.

 

It defeats the object of having dimmable lights.

Edited March 17, 2017 by mistermack

[StringJunky]

You need to be careful when buying dimmable systems.

If the objective is to save energy, you may be wasting your time on dimmable ones, because the electronics involved in dimming them might be just dumping the extra energy as heat.

I have a couple of LED torches that work on batteries.

One is dimmable and the other is not. They both have the same Cree T6 LED and both are very good and bright.

But the dimmable one gets warm, even when dimmed, and the battery actually doesn't last as well as the non-dimmable one, even if it's on the lowest brightness setting.

Clearly, the reason that it gets warm in the hand is because the electronics are dumping some power as heat, in order to make the thing dimmable.

 

It doesn't really affect the use of it, but it's ironic that the non-dimmable one on full power lasts longer on it's battery, than the other on the dimmest setting.

 

It defeats the object of having dimmable lights.

If the purpose is to save power.

[mistermack]

If the purpose is to save power.

Yes of course. That's the stated purpose in the OP, but in the case of the torches, I guess there could be times when you want to dim it for other reasons. I find it pretty easy just to put a finger over the lens, if I want a dimmer light.

 

In the case of torches, I think what would be ideal would be to have an optional selectable low-power LED, rather than some electronics to dim the supplied T6. You would get more battery life that way, than the set-up that's in the dimmable one.

The one I have that isn't dimmable has a much longer battery life, on the same batteries.

 

Some LED torches that have multiple LEDs can select different numbers of LEDs to light up, I think that's a better system.

[StringJunky]

Yes of course. That's the stated purpose in the OP, but in the case of the torches, I guess there could be times when you want to dim it for other reasons. I find it pretty easy just to put a finger over the lens, if I want a dimmer light.

 

In the case of torches, I think what would be ideal would be to have an optional selectable low-power LED, rather than some electronics to dim the supplied T6. You would get more battery life that way, than the set-up that's in the dimmable one.

The one I have that isn't dimmable has a much longer battery life, on the same batteries.

 

Some LED torches that have multiple LEDs can select different numbers of LEDs to light up, I think that's a better system.

I have a bike light that dims. Apparently, it works by reducing the number times it flashes/pulses. I noticed that the tread on my tyres was strobing and it was explained to me that the emitted light is not continuous... on a cheap one anyway, like mine is.

[koti]

I have a bike light that dims. Apparently, it works by reducing the number times it flashes/pulses. I noticed that the tread on my tyres was strobing and it was explained to me that the emitted light is not continuous... on a cheap one anyway, like mine is.

 

Dimming in LED's is done by PWM (Pulse Width Modulation) It's a technique of varying brightness of the emitter by flashing it on and off very quickly, making it appear to the eye that the LED is dimmer. "Good" PWM is considered at such a high rate that you can't notice it.

So yes Stringy, that somebody gave you accurate information

BTW, and I hope I will not be getting a second warning for advertising this...in the next 10 days or so I will be releasing a small batch of my small, handheld, pocketable custom flashlights with advanced firmware, latest XP-L2 emitter, a custom driver and a dedicated bike mode for all the bikers out here. I will be selling a complete package including a high drain 18650 LiIon cell which is needed for this light and a small portable charger to go with it. PM me if anyone would be interested in a small monster flashlight in your pocket.

[StringJunky]

 

Dimming in LED's is done by PWM (Pulse Width Modulation) It's a technique of varying brightness of the emitter by flashing it on and off very quickly, making it appear to the eye that the LED is dimmer. "Good" PWM is considered at such a high rate that you can't notice it.

So yes Stringy, that somebody gave you accurate information

BTW, and I hope I will not be getting a second warning for advertising this...in the next 10 days or so I will be releasing a small batch of my small, handheld, pocketable custom flashlights with advanced firmware, latest XP-L2 emitter, a custom driver and a dedicated bike mode for all the bikers out here. I will be selling a complete package including a high drain 18650 LiIon cell which is needed for this light and a small portable charger to go with it. PM me if anyone would be interested in a small monster flashlight in your pocket.

Cheers.

[mistermack]

That's a good spot. I just tried my torches to see if they strobe. (simply waved them fast in front of my face).

You can see the on/off clearly.

The plain torch with no dimmer setting doesn't strobe. The one with the dimmer doesn't strobe, on full power, but does, on dim.

Not something you would notice, unless you were told it, or noticed it in your bicycle wheel.

 

It's a mystery why that one gets warmer, and has poor battery life, whereas the other doesn't.

It might just be a poorer design, not related to the dimmer circuits.

But it does get warm, even on dim, and even on dim the battery does run down faster.

 

They both use a quality 18650 Lithion cell, they are great batteries, and seem to hold full charge for ever if you don't use them.

A huge improvement on NiMh.

[Bender]

Bycicle lights can strobe even without dimmer, because alternator produces alternating current, so when it goes through zero, and there is no cfpacitance in your light, it goes out at least twice every revolution. In very cheap lights, it is possible that it is off half the time, because LED's are polarised and conduct the current only in one direction.