Fluorescent to LED night light conversion

[jtr1962]

I've been cleaning my workshop lately ( one reason I'm not on CPF much last few days ), and came across an old flourescent night light:

I remember it had died about a decade ago, and I put it aside in hopes of eventually doing something productive with it. Truth is I was ready to toss it but I needed a break from the cleaning. Just as luck would have it all the little pieces which made the project feasible where in place. That's when the brainstorm came. The Osram LW E6SG surface mount LEDs which I picked up on eBay would be perfect candidates. They had held up well in several LED night lights I put them in. And JohnR66 has an ongoing fade test in which they show no degradation so far at 39 mA.

OK, so I made the decision to mod the light. This was obviously a more ambitious project than just replacing stock LEDs as I had done with my other LED night lights. Moreover, I wanted the output to at least rival the output of the original fluorescent tube ( I think it was a 2 or 3 watt tube-overall power usage for the tube and ballast was 3.5 watts ). No idea of the output, but most small fluorescent tubes aren't particularly efficient. I'd be surprised if the tube put out more than about 50-60 lumens.

The circuit I decided to use was simply the classical capacitor-fed full wave-bridge. The basic principals are discussed here. I first removed the original innards:

And I replaced them with the new driver circuit made up of parts I had handy:

The hard part was mounting the LEDs on a board. I decided to use 24 in series because that's what fit evenly-spaced given the size constraints:

After wiring everything up, I took a few measurements. The LEDs were being driven at around 20.7 mA, and the total forward voltage of the string was 78.9 V. Total power consumption from the mains was around 1.7 watts. As a finishing touch I put some foil duct tape in the large blank area between the rows of LEDs. The idea was to have a nice reflecting surface so everything would appear uniform:

I put the diffuser on and fired it up:

Finally, I put the night light in its place of honor, the bathroom:

The picture appears roughly how it looks in person. My tests of the Osram LED extrapolate to about 3.2 lumens at 20.7 mA. So that's about 75 lumens total, probably more than stock, and using half the power. More importantly, the light stays fairly cool, and should last many thousands of hours.

 

[Paul Baldwin]

I wish the little project lights I threw together looked that neat! Nice use of re-cycled parts too, very green, that lights been waiting patiently for you for a decade lol.

 

[jtr1962]

I found two of these night lights in brand new condition. Here's the bathroom lit with the stock fluorescent tube ( with the LED version for comparison below ):

CCT of the tube is slightly lower than the LEDs, and the beam is a little smoother ( although sanding the diffuser would probably smooth out the LED version ). Overall light output looks pretty similar to my modded one actually, perhaps marginally less. Not shown is that the flourescent tube flickers at 120 Hz, and the night light makes a slight buzzing sound ( you only notice this if the room is really quiet ). None of these issues exist on the modded light.

Well, when the stock fluoro tubes go on these other two lights I'll have another modding project.

 

[JohnR66]

Nice modding job.:thumbsup: I have one of those fluoro nightlights around somewhere just waiting to be hacked.

The Osram LED is well over 1000h now with no fading. JTR sent me some even smaller Nichia surface mounts for testing. I'll report when I get some hours on them.

 

[Paul Baldwin]

You can see from the wall switch that more of the light from the leds is directed forwards. Could you cut the board they are mounted on down the middle to angle it down a bit? I'm thinking you dont really want to angle it upwards as they will shine directly at you.

 

[jtr1962]

You can see from the wall switch that more of the light from the leds is directed forwards. Could you cut the board they are mounted on down the middle to angle it down a bit? I'm thinking you dont really want to angle it upwards as they will shine directly at you.

The board is glued down with hot melt glue, so I'd rather not mess with it at this point. Looking at the light now, I think the foil in the center area was a mistake. That's what is producing the two "beams" widely angled from each other. I might replace the foil with matte white plastic. This should hopefully make things a little less specular. Other that that, I'm pretty happy with the way this project turned out. When the other two night lights burn out, I'll fine tune what I did here.

On another thought, as great as these Osrams are, it's a pity they haven't released a higher efficiency version ( these are 50 lm/W @ 20 mA which isn't terrible, but higher is always better ). Or if Nichia's Raijin were less expensive and more readily available, I could have had either 1/3 the power consumption for the same output, or 3 times the output at the same power consumption. But honestly, minor things like this aside, the project turned out better than I had hoped for. For $4.80 worth of LEDs plus a little time, I turned potential landfill into a very useful item.

 

[jeffosborne]

Well done, jtr1962! The minimalist power circuit is refreshing. And the finished mod is a winner.

Your proto board soldering is very tidy, I'd say you've practiced quite a bit. Sometimes I find soldering to be therapeutic. And rewarding.

The Osram LED color looks a little less warm than the incan, but not at all cool on your nearby tiles. Were they 5000K?

Maybe a piece of rice paper inside the cover would tamp down those light stripes on the side.

Thanks for sharing your mod! Good luck with your workshop cleanup.

Jeff O.

 

[jtr1962]

Well done, jtr1962! The minimalist power circuit is refreshing. And the finished mod is a winner.

Thanks! Besides low parts count, the capacitor-fed full-wave bridge is surprisingly efficient. The only losses are in the 150 ohm resistor ( needed as a safety feature in case the 1 uF cap fails, and also to clean up the voltage spikes a bit ), the bridge diodes, and some minor losses due to capacitor impedance. Going by the numbers I measured, 1.633 watts of the ~1.70 watts it's pulling from the mains is going into the LED string. That's 96% efficient, give or take a few percent.

EDIT:

Here's the schematic in case anyone is interested:

Your proto board soldering is very tidy, I'd say you've practiced quite a bit. Sometimes I find soldering to be therapeutic. And rewarding.

Actually practiced a lot. My business involves building up to 500 surface mount regulators at a time. Suffice it to say I have soldering down to a science. Yes, I also find soldering to be therapeutic, especially laying out parts on a proto board. It even helps my CTS to some extent, provided I don't over do it.

The Osram LED color looks a little less warm than the incan, but not at all cool on your nearby tiles. Were they 5000K?

They're roughly 5500K, but I'd say the diffuser had a slight touch of yellow, so that's bringing the CCT down to around 5000K. And the tile color looks pretty close to how it looks in daylight.

Maybe a piece of rice paper inside the cover would tamp down those light stripes on the side.

I'm thinking of doing something like that. Perhaps I'll find something suitable in the course of going through my things.

Thanks for sharing your mod! Good luck with your workshop cleanup.

Thanks again! The workshop cleanup is a major ordeal which will probably take the better part of a week. Lots of parts I just came into which I threw into the cabinets without really organizing them. I need to do this so I can work more efficiently again. I know it gets bad when I can't find things I know I have. That's been happening too much lately. And the opposite as well-finding things I forgot I had, like this night light.

 

[jtr1962]

Well, I found another night light, and was thrilled when it didn't turn on! Time for another mod:

This time I put the two rows of LEDs closer together:

I found something which works reasonably well as a diffuser ( a plastic milk container, believe it or not ):

And here's the finished result:

Note how much more even the lighting is. The "diffuser" does cut down on the output a bit, I'd estimate 10% give or take, but it's barely noticeable. The improvement is well worth any loss in output. I'll also add that I put in a 22 µF filter cap instead of 100 µF because that's all I had handy. There is no visible flicker, so I guess 100 µF is overkill for this application. The nice thing about using 100 µF however is that the LEDs visibly glow for over a minute ( and glow brightly for a few seconds ) after turning the light off. With the 22 µF cap the LEDs ramp down almost instantly, and only glow maybe 10 or 15 seconds ).

EDIT: In case anyone else has this same light, the size to cut the diffuser is 54 mm x 98 mm ( 2⅛" x 3⅞" ).

 

[Paul Baldwin]

That now looks like a "boughtun" as they may say round here That diffuser really does the trick! I've been using strips of 3M Transpore tape, the sort you use to hold dressings on. My mothers a nurse so always has a bit kicking around. I was going to suggest it for your other light but now I see there is no need

 

[eyeeatingfish]

is there any sort of good idiot's guide for how to do these kind of mods? I would love to be able to mod various house things with energy saving LEDs but I dont know where to start. I can barely solder and I dont know about how to figure how many resistors etc. And a lot of the LED bulbs you buy are kind of expensive, $40+. Maybe worth it in the long run though....

 

[jtr1962]

Four years later and both modded nightlights are still working great! We usually forget to turn them off, so I could probably say they're on an average of at least 16 hours per day, probably more like 20 hours. That's ~25,000 hours in four years. To my eyes they seem as bright as the day I modded them, if not slightly brighter.

On another note, Osram now has much more efficient LEDs which I'll be using if I mod any more night lights. The ones I used in these lights achieve ~50 lm/W @ 20 mA. I have some Osram surface mount LEDs from Mouser which achieve ~120 lm/W @ 20 mA. They are available in CCTs from 2700K to 6500K to suit anyone's preference ( the low CCT ones are slightly less efficient ).

 

[Illum]

decided to make one based on this [finally] and got a little taste of the shock factor when I accidentally switched the hot with neutral. When the power supply is connected as shown in your drawing, the negative rail is 0.7v above neutral. If the mains is reversed, the negative rail is 170v (peak) above neutral. Good news is, I'm still here, and the circuit was more or less isolated via the old tired variac, which allowed me to monitor the progress as I slowly increased the forward voltage.

Got me thinking...I have several common mode chokes desoldered from florescent ballasts, printer supplies, etc. Given the low current nature of this project, could a common mode choke be used as an isolation transformer? Efficiency might take a hit, but it sounds theoretically possible.

 

[parametrek]

could a common mode choke be used as an isolation transformer?

No, that does not work. Common mode is the opposite wiring of isolation. See this picture of a basic Common-mode_choke wiring. Zero safely because you still have a short-circuit path to the mains.

edit: Unless you meant putting a common mode choke in "sideways" so it appears as an isolation transformer? Probably also not going to work, unless the choke is really big and it uses iron instead of ferrite.

 

[Illum]

edit: Unless you meant putting a common mode choke in "sideways" so it appears as an isolation transformer? Probably also not going to work, unless the choke is really big and it uses iron instead of ferrite.

That was what I had in mind yes...
hmm... I'm not sure if iron core chokes exist

 

[FRITZHID]

Build one.