Saturday, April 09, 2011

Tweaking $6 LED Lamps


Part 2 of 
Tweaking $6 LED lamps

I have several rooms in my house where I have either MR16 or GU10 type spotlight lamps in various fittings. These fitting have had either 35 watt or 20 watts halogen bulbs in them. I had previously tried some cheap Chinese LED lamps and was very disappointed with them on several accounts:

1. The colour of the light was inconsistent.
2. The light output was low and in some cases, so low as to be little more than a joke.
3. The light colour was unstable and changed towards the blue - purple over a relatively short time of use - six months or so.
4. The lamps failed completely very often.

Second Generation of Cheap LED Lamps

More recently I was seduced by the idea of affordable LED lamps again and scummed to temptation and ordered several lots of GU10 and MR16 4watt warm white LED bulbs. Typical construction included 4 x 1 watt LEDs fixed onto a baseplate, which in turn fitted into a fairly reasonable quality aluminium heatsink.

First impressions of these newer type lamps were that the light output and colour was GREATLY improved on previous offerings. However, about 20% of the bulbs failed or partially failed inside of four to five months use of about 12 hours a day..

The Fix - or possible Fix!!

I decided to investigate and try to find the reason for failure. So my first efforts were to find how these bulbs were put together.

Both the MR16 and the GU10 lamps, as shown above,  have a very similar mechanical construction. The lens rim screws off and allows the lens to come away. Behind the lens are mounted the four LED elements. The LEDs are fixed onto a metal mounting disc. This disc is then fitted into the heatsink.

The problem of blowing LEDs IMHO is mainly caused in these Chinese lamps by the total lack or insufficient quantity of thermal heatsink paste at the point where the mounting disc meats the heatsink flange. LEDs generate a lot of heat and the heat must be carried away efficiently and quickly or the LEDs will be damaged or fail completely.

Two months ago I ordered another bunch of LED lamps. This time, before used them I checked each lamp for thermal integrity.  In 8 lamps, I found two with NO THERMAL PASTE - at all.  I found two more with patently insufficient amount of thermal paste. 

I put plenty of CPU type thermal paste on the heatsink flanges of these lamps and they have been burning for 15+ hours a day since - and none have failed or blown in this batch.- I hope I have cracked it!!

The cost is only a few cents per lamp and about five minutes of my time. I now hope that I have good quality LED lamps. 

At $6 a piece including the shipping - that cannot be bad value - even if you have to put a little work into it!!


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