The Not-So-Bright LED Night Light

In theory, a LED light should last for ten years or so, unlike the typical 4W incandescent lamps used in night lights that seem to burn out in only a few months. But as engineer and founder of the website Discover Circuits Dave Johnson discovered, this Chinese-made unit from Costco (apparently designed by some real dim bulbs) didn’t last but 12 weeks:

“I bought a pack of three of these night lights, made by Elumina Lighting Technologies, for about $15. The unit has a pushbutton switch to toggle between settings (dim and bright) and a CdS photocell that turns off the device during the day.

nightlightmod5.jpg nightlightmod8.jpg

Inside are three white LEDs, wired in series. When I first plugged the device in, it seemed to emit an acceptable amount of light. But in a short time, the light gradually faded until it was virtually useless.

This has happened to me several times with other inexpensive LED lights. I think some manufacturers from China are using inferior phosphors inside the LED assembly, which fatigue after only a few hundred hours. Opening the thing up, I traced out the circuit and determined it was one that I could easily modify.

nightlightmod6.jpg I made some component value changes and pulled out the three dim LEDs and replaced them with 10 high quality, super bright surface-mounted units from Osram Opto, which I soldered together into two strips of 5 LEDs each. I paid about $1.00 each for the LEDs. So now for an extra $10 per unit (and therein lies the engineering trade-off!), the light now emits a nice bright white light and should last many years with no risk of someone taking a header down the stairs in the middle of the night!”

View additional product images and the original and Dave’s redesigned circuit , which uses a classic series capacitor method to produce a current limiting LED driver, powered from the AC line.

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8 Comments

  1. Mitch
    July 15, 2013 19:45

    As the original designer of these EXACT Led night lights, I should play devils advocate.
    The design process for these lights started in 2005. and from concept sketch to production ready prototype was 6 months. You seem to understand technology so you must also realize that LED technology has changed drastically since the first LED bulbs were available for mass production. Even from 2005 – 2007. The lights you have swaped were not even Invented for us to use in 2005.

  2. July 17, 2012 05:19

    This bulb is expensive as most LEDs are coemarpd to compact florescent and others. For the money this is about as good of an LED spotlight one can buy. It does have the normal LED problem of spotlighting but it is not as bad as the cheaper and weaker products I’ve tried. I have it in a location where I always want a light on and it does a good job of lighting up the area (hallway). This bulb is not for everyone giving this price point, but if you are looking for the best LED for the money this is the best I’ve found.

  3. Green Consumer
    October 28, 2009 02:01

    I am a big fan of LED lighting. Choose a bulb that fits the application (lumens and color) and you will be happy. Unfortunatly many manufacturers and vendors overstate (I’m being kind here) their products specifications.
    I have purchased 45 LED bulbs and have had mixed reliability.
    The good news – some are very reliable. I have five LED bulbs outside that have run dusk to dawn for two years with no problems.
    The bad news – some bulbs are VERY unreliable. VERY high failure rates.
    I purchased 12 of one type LED bulb and 7 have failed (8.5W product 47856 from LEDLight.com). To make matters worse they are refusing to replace them now.
    Beware of LEDLight.com. These bulbs are very expensive ($20 – $105) and in some cases last only two or three weeks. They refuse to replace defective bulbs. [Comment edited by Webmaster]

  4. Tim Howes
    May 12, 2008 14:46

    Hi I had the same problem with some spot lights.
    They had 36 LED’s in series a bridge rec and two resistors one in series with the limiting cap (just a few k) and one across the capacitor I assume to avoid you getting a belt from any stored energy just as in Clive’s picture. As the capacitor is effectively a high pass filter it is no wonder they die so young. Estimated life 30,000 hours actual about 1000 hours but they were no good as effective light long before then. I paid a lot of cash for lighting that was supposed to last a lifetime and had a long battle with the seller to no avail as they are considered to be consumable (ultra fun).They modified there claims to at least as long as a filement woopie doo considering they cost 20 times more. I now have compact florescent GU10 bulbs they have worked fine.

  5. Gary Henderson
    September 03, 2007 23:11

    Hi
    Opto devices of all kinds are extremely sensitive to over-current spikes due to mains transients; this is partly because they must use very fine bond-wires to avoid internal shading of th eactive surface; also the thermal properties of transparent packages are inferior to normal mineral-filled semiconductor housing plastics. The use of a series capacitor as a ‘current limiter’ is a great way to leave the door open for any spike that chooses to drop in! The peak-current rating of the LEDs must be protected by a resistor or (less likely!) an inductor. In absence of detailed device information, a value to limit at about 1A would be the minimum (120 or 220 ohms, according to your local mains voltage).
    If a shunt resistor or zener is to be used to cope with the “Off” situation, why turn the LEDs off at all? Better to provide a capacitor at C1 rated for rectified-mains operation – these are commonplace since the advent of switching-supplies in wall-warts.

  6. Bernard Green
    August 01, 2007 15:04

    “This LED has a life time guarantee” is used as a selling point….
    Define the life time please……

  7. June 15, 2007 22:38

    same problem for me with led night-lights, though they took the better part of a year to fade. i’ll try replacing the leds for starters and later go for the better-led solution if i have the time.
    thank you SO much for identifying at least one of the causes! my first guess was that a “series dropping” capacitor had gone bad… i actually believed the claims about long-lived leds.

  8. April 26, 2007 11:42

    Although poor quality LEDs are a major part of the problem with the mains powered LED lights, another significant factor is the type of power supply. These lights tend to use a capacitive current limiter that allows a small portion of current through on each half cycle of the mains supply. Unfortunately if there’s any electrical noise on the mains the LED light will also do it’s best to shunt it through it’s load like an interference suppressor and this an subject the LEDs to quite high current pulses. It’s a good idea to add a modestly beefy current limiting resistor of at least 240 ohms in series with the mains input to the capacitor.
    I’ve got some early plug-in LED night lights that I’ve hacked to improve. One of the most interesting features of the original circuit was the way it turned out the LEDs during the day. It just shorted them out! The unit actually took a slightly higher current when the LEDs were off!
    For reference, 240V versions of this circuit use a 330nF capacitor.
    Here’s a link to a picture of a super-minimalist LED lamp based on the capacitive limiter being tacked across the back of the LED PCB.
    http://www.emanator.demon.co.uk/candle2.jpg

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