# Emitter (And electronics) choice for a pleasant (High CRI? Low temp?) bedside lamp



## ftql (Oct 20, 2015)

Hi,

I'm currently thinking about making a small bedside lamp and I'm in the process of understanding the design space by considering potential emitters, drivers, controls, dimmers, power-supplies...

My current thoughts on it are the following.

My main goal is to have a pleasant bedside lamp. By pleasant I'm thinking about the quality of light, but also of the lamp and its ergonomics (Switching and dimming the lamp, moving it, plugging it to a wall...)
An important constraint is to keep things simple enough for me to actually be able to make the lamp and not add it to my ToDo pile. Keeping in mind that it is my first lamp project.

To fix a few ideas here are a few constraints/estimates I was thinking about, all being challengeable:

Max luminosity around 1000 lumens (Balance between having enough light to influence room ambiance in the evening and keeping things small and cold enough).
Dimmable to low levels. It doesn't have to be continuous but I do like the feel of a smooth potentiometer and light dimming.
Non audible electronics.
Non visible flicker even at low levels.

*Emitter
*As far as the emitter go, I was initially targeting high CRI (>92) and low temperature (~2700K) to get a warm and cosy natural feeling. From what I read down here I understand that things are not as simple as this and that high CRI and 2700K do not guarantee a 'natural' bedside ambiance.
*What kind of leds should I look for if my goal is to have a pleasant light and I cannot rely on simply selecting highest CRI and lowest temperature I can get?
*
A few specific led manufacturers I've been looking at:

Xicato which some CPFers seem to rave about. Xicato modules do not seem to be thoroughly available to purchase though (But I was able to find one on eBay) And they seem quite expensive.
Sharp Zenigata leds seem nice.
Bridgelux
Cree
Osram
Nichia (Which advertises a Candle Color range (2580K-1870K) which sounds interesting for a cosy feeling but I couldn't find any emitter below 2700K)
And should I look at bare emitters or is it worth it to considers modules with integrated drivers?

*Power supply
*I don't want the power supply to be an afterthought as it can be hard to find a good quality and compact power supply in the 15-20W range that I'm considering. The integrated one are often a bit underpowered (Example) or have a voltage which requires to be boosted and limit driver choice (Example) or are fine but bulky and ugly (Example).
A fun power supply I'm considering is the... Apple 29W usb charger which can deliver can deliver 2A @ 14.5V and might be of excellent quality (http://www.righto.com/2012/05/apple-iphone-charger-teardown-quality.html). It would requires a Power controller chip though (Example) Standard USB Power Delivery protocol even allows 5A at 20V

*Driver*
I'm considering a driver that would allow to easily dim the led through a potentiometer such as http://www.ledsupply.com/led-drivers/buckpuck-dc-led-drivers It would requires the led forward voltage to be below my power supply output voltage though.


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## brickbat (Oct 20, 2015)

I've had in mind a similar project. 'Pleasant' light is subjective. I experimented with some Cree CXA1304 CoB arrays - 3000K, 90+ CRI. I found that when dimmed they are too cool-looking for my taste. I don't have a way to measure if the CCT is shifting as they are dimmed, but I just want something warmer at low light levels.

So, I'm pondering adding in a 2nd warmer source - maybe a Luxeon 2200K 90 CRI L2C3 array. The only way to know is to order one and tinker with it. They're in-stock at Mouser and pretty inexpensive...

Then the two sources have to be blended so I don't get multi-color shadows. Not sure what the best solution is for that in my case.


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## FRITZHID (Oct 21, 2015)

I have a dedomed xml2 3000k +92 CRI in my beside light that I love. Dim or bright, light is very close to halogen. Imho


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## SemiMan (Oct 21, 2015)

Nichia 2000K LEDs are available. It's buried in the data sheet for the 3000K (warm) data sheet.


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## ftql (Oct 21, 2015)

Thanks for your comments.

So you three seems to agree that I should look at warm emitters and SemiMan and Brickbat you even encourage me to look at led warmer than 2700K. I knew that I wanted something on the warmside but I wasn't sure that I should look below 3000K. Thanks SemiMan for the Nichia Tip. I didn't understood why some leds were rated as Candle Color(2580K-1870K) but only 2700K leds were displayed. Those leds indeed have warmer variants described in the data sheet.
http://www.nichia.co.jp/en/product/led_product_data.html?type='NJCLS024Z' for example has a 2400K version
I didn't find anywhere to purchase those below 2700K versions though. (But this 2700K one seems readily available: http://www.leds.de/en/High-Power-LE...ard-Modul-Serie-36-warm-white.html?force_sid=)

On the driver side, those leds do not seem super easy to drive, as the forward voltage can be up to 40V. I will try to dig a bit deeper at that driver thing. Maybe I could drive them at 350mA as I don't need the full brightness.


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## SemiMan (Oct 21, 2015)

Just don't read at 2000k  Higher is better.

40v is easy. Lots of AC drivers for that.

Posted by really crappy Tapatalk app that is questionable wrt respect of personal data.


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## brickbat (Oct 21, 2015)

Does Nichia have any US distributors that sell in single quantities?


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## ftql (Oct 22, 2015)

Ok, I think I've chosen the emitter I want to use for my bedside lamp project. I think I will go with Sharp Tiger Zenigata GW6NGWJCS0C (http://www.sharpsma.com/download/GW6NGWJCS0Cpdf).


It's the warmest emitter which can easily be bought I could find. I didn't manage to find places where to buy the 2000K Nichias.
It goes down to 2000K at ~100 lumen at a ~94 CRI.
It has this fun dim to warm feature ("At an operating current of 350 mA, the ZENIGATA delivers up to 1000 lumens with a colour temperature of 3000K. When dimmed down to 50 mA, the Mini puts out 105 lumens at 2000K.")
Mouser stocks it and sells it in single quantities (http://www2.mouser.com/ProductDetai...Fc4E52DLCza4s54PjaeJSjoHkHDM23KCzTmbTAEFDMg==)
It's in budget (~20$)

*Driving the Sharp Tiger Zenigata GW6NGWJCS0C 
*

240V AC input
Output voltage > 40.2V
Can dim from 350mA to 50mA (100-15%)
Is above 15W
I think I will go with Meanwell LCM-25 which seems to be a good quality and very versatile driver for future projects (http://www.meanwell.com/search/LCM-25/LCM-25-spec.pdf)

I was thinking of dimming it with a 100KΩ pot. Any idea of the power rating for the pot I would need. I couldn't find any info in Meanwell spec sheet.


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## brickbat (Oct 22, 2015)

There's no concern with the 100k pot power rating - pretty much any one will do. I might be inclined to tinker with audio/log taper pots to get a better dimming vs. pot position function.

I LIKE the Sharp LED you found. I'm intrigued - hadn't seen that before....

and I like this one too: http://www.mouser.com/ProductDetail...=sGAEpiMZZMu4Prknbu83y4PIPQP9w0HVgsI4faiSIEQ=

Any competitors in this 'tunable' space offering newer devices with better efficiency?


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## Marcturus (Nov 4, 2015)

LED seems to be rare or special order from Toshiba:
http://trir-pj.com/

a 2500-2900K application:
http://themodernshop.ca/products/ingo-maurer-lucellino-led-table-lamp
(please, please do NOT look at the price before offering your products at the CPF Mall!)


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## Steve K (Nov 4, 2015)

ftql said:


> I was thinking of dimming it with a 100KΩ pot. Any idea of the power rating for the pot I would need. I couldn't find any info in Meanwell spec sheet.



Looking at some of Mouser's panel mount pots, they tend to be 0.25W or so. My guess is that there's no more than 10V that will be across the dimming terminals of the power supply, so the power dissipated in the pot will be V^2/R, where V is 10 volts.

With a 100k pot, you will turn it down to 10kohms for dim light. The power dissipated at 10kohms is 10^2/10k, or 0.01 watts. This is within the ratings for just about any pot. 

The real risk is when you turn the pot down to nearly zero ohms. The power ends up being dissipated in a very small part of the resistive material, and it is possible to cause damage. For this reason, it's not a bad idea to wire a small resistance in series with the pot.... maybe 5kohms? 
Or, you could make a few measurements and see how the power supply is driving the dimming inputs. That should help guide you to the best answer.
I think you should be in pretty good shape regardless.


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