LEDs - For the curious

[XFool]

Some while ago I purchased in a B&Q closing down sale a Diall brand 9.5W 806 Lumens LED light bulb (my first!). It was supposed to be dimmable, equivalent to a 60W incandescent and have a 15,000hours life. It lasted about 15 seconds. Usually careful about such things, on this occasion I had lost the receipt.

I found it lying around today and decided to investigate before disposal. Firstly I tried to smash the bulb with a heavy wine bottle and the light safely in a plastic bag wrapped in a towel. Several heavy blows revealed it to be plastic, not glass. So I sawed my way in with a small hacksaw.

The LED light consisted of a circular aluminium disc with fourteen LED chips arranged with eight around the perimeter and six in a central block. A thick plastic 'lens' diffuser structure was mounted above the central block of LEDs. A pair of small folded metal 'clips' formed a pinch connector to two metal pins coming from the little power supply PCB which was slid into a surprisingly heavy duty sintered type metal base.

It may make sense for the power supply to be surrounded with metal, but why such a heavy duty base, which accounts for most of the weight of the whole light?

Why did it fail? Well, the two pins from the PCB going to the pinch connectors looked to me a possible weak link. The pinch connectors did not close tightly when the LED disc unit was lifted and the PCB pins while not definitely corroded looked far from shiny clean and had solder on at least one side. It occurred to me it could still possibly work in this condition (unlike an incandescent bulb) so I worked the pins against the LED disc connectors, put it back in place and carefully put the whole thing into a lamp socket and turned on. Nothing. So likely it was the electronic power supply that had failed.

[AleisterCrowley]

It may make sense for the power supply to be surrounded with metal, but why such a heavy duty base, which accounts for most of the weight of the whole light?
I'd guess heatsinking, reducing operating temp.

[gryffron]

but why such a heavy duty base, which accounts for most of the weight of the whole light?

Back in the 80s when satellite TV first launched, you could buy a box from Amstrad or Pace. They had identical innards, price and capabilities, but initially the Pace box outsold the Amstrad >2:1. Amstrad couldn't understand why. So they did some research in the shops and found customers picked up both boxes, then bought the Pace one because it was heavier, and thus perceived to be "better quality". Amstrad added a lump of useless steel in the bottom of their box (which the Pace box already had) and matched sales 1:1.

Heavier weight = "better built" in the perception of customers. Probably still true for light bulbs. People are used to heavy glass lightbulbs, and a lightweight plastic one would be perceived to be inferior.

Gryff

[Watis]

Four years ago, I purchased three LED bulbs for a three branched light fitting.

Two years ago, one of the bulbs failed and was replaced with the currently available bulb. Although it is equivalent in light output, it is only about half the weight of the older bulbs!

I don't know whether the new bulb runs hotter or cooler than the older two bulbs but you've piqued my curiosity, so perhaps I'll check.

Watis

[bungeejumper]

I have now transitioned the whole house to LEDs - and that's more than 70 bulbs. Shhhhhhh!....The wife only knows about half of them - I'm waiting for her to eventually twig that LEDs are just as good as the tungstens that she used to claim were much better.

As for heat, it if says it uses 5 watts I expect it to use 5 watts. Am I being naïve?

BJ

(Top shed deal at the moment is probably B&Q's three bayonet bulbs for £4.50. They seem fine - I haven't checked whether they're dimmable - I doubt it.)

[gryffron]

As for heat, it if says it uses 5 watts I expect it to use 5 watts. Am I being naïve
...
(Top shed deal at the moment is probably B&Q's three bayonet bulbs for £4.50. They seem fine - I haven't checked whether they're dimmable - I doubt it.)

It will use 5w of electricity. A good LED, about 25% visible light. So 1.25w of light and 3.75w of heat. That isn't much. Just about enough to feel warm. Certainly wouldn't need a heat sink.

My pound shop have 5w/300lumen LeD bulbs. I find them quite adequate for hall, bathroom and bedrooms. Though insufficient for a big lounge or reading light.

Gryff

[jfgw]

As for heat, it if says it uses 5 watts I expect it to use 5 watts. Am I being naïve?

If it something cheap off of eBay, I would expect it to use about 2.5W

Julian F. G. W.

[PrincessB]

I'd guess heatsinking, reducing operating temp.

I understand that the life of an LED declines dramatically if it gets overly hot.

Specialist LED company Dialight were quite inovative with their LED stobes that are placed at the top of communications towers - you don't really want these to fail as changing one involves climbing up a huge tower in the back end of nowhere while lugging a very heavy lighting module in one hand.

See:
https://www.youtube.com/watch?v=hFMHjDqHL_Y&t=12s

You would like them to last for as long as possible so the solution was some really big peltier cooling feeding impressive heatsinks.

This would of course use quite a bit of power but as the idea of an LED was to last as long as possible, having a inefficient cooling solution turned out to be the right decision.

Agree with the Philips bulbs, I have a set of four 1500 lumen units with impressive build quality including finned alumunium cooling fins and a hefty weight. Unfortunately 6000 lumens was not sufficient for the kitchen and they had to be replaced with some 1921 lumen units which make a big difference.

B.

[AleisterCrowley]

I just couldn't watch that YouTube clip..my palms were sweating


I understand that the life of an LED declines dramatically if it gets overly hot.
Yes, I've seen some graphs from Cree that show this.