lm/w for ordinary cheap 5mm leds?

[Flummo]

Does anyone know how good the cheap chinese 5mm leds are when it comes to lm/w? This kind of leds are usually rated in cd/mcd only, and for an amateur that is hard to compare to something rated in lumen.

 

[Illum]

until you can drive a 5mm match-head with 1 watt of power without frying it the value of lm/w is so small its insignificant and vague to rate 5mms. Hence the utilization of mcd or luminous intensity value for specs for LEDs, usually with other parameters, such as junction temperature, forward voltage, etc.

Different 5mms yield different values depending on which spectrum they are designed to emit.

 

[Calina]

Good white 5 mm LEDs provide about 4 lm at 20 mA (about 60 lm/W). Expect about 10 lm when driven at 60 mA, but they're dropping rapidly.

I think the very best ones now reach around 6 lm at 20 mA, but please correct me if I'm wrong.

 

[jtr1962]

Good white 5 mm LEDs provide about 4 lm at 20 mA (about 60 lm/W). Expect about 10 lm when driven at 60 mA, but they're dropping rapidly.

I think the very best ones now reach around 6 lm at 20 mA, but please correct me if I'm wrong.

Probably closer to 5 than to 6. It seems 5mm LEDs have petered out, with the majority being in the 60 to 70 lm/W range at 20 mA (~4 lm@ 20 mA), but a few better ones such as the Jeled 55,000 mcd hitting perhaps 80 to 85 lm/W. Nichia allegedy promised to release 150 lm/W whites this year or next, but I haven't even seen the 100 lm/W ones promised last April out yet. Most of the R&D these days is going into power LEDs. I guess for most very small lighting uses 60 to 80 lm/W is considered "good enough" by LED manufacturers. Another possibility is that all of the higher-grade blue chips are being using for applications like cell-phone backlighting, leaving the less than prime grades for commodity 5mm LED manufacture. That would certainly explain the apparent stagnation of efficiencies for the last year or so, although I think average efficiencies of the really low grade stuff is still rising. A year ago the super cheap (i.e. less than $0.05 in quantity) white 5mm LEDs might only manage 20 or 30 lm/W. Today they're probably doing 40 or 45 lm/W. The premium stuff has been stuck at around 80 to 85 for a while though.

Remember that an 80 to 85 lm/W white requires a blue chip with an efficiency of around 33%. That would mean approximately 21 mW of light energy at 20 mA. Getting much above this efficiency is still probably proving to be difficult and expensive in mass production. They have made blue chips with >75% efficiency in the lab. Once these go into mass production, we'll probably have 150 to 180 lm/W 5mm whites. As for when, that's anyone's guess.

 

[Flummo]

Okay, thanks!

 

[Calina]

Probably closer to 5 than to 6. I haven't even seen the 100 lm/W ones promised last April out yet.

I thought these were out and were the new DS, hence the 6 lm. They're more than due.

 

[jtr1962]

I thought these were out and were the new DS, hence the 6 lm. They're more than due.

I know about the specs for the new DS. However, extremely limited availability at ridiculous prices isn't "out" in my book. When you can buy these for a similar price to the CS at the Nichia store, and get all you want, I'll consider them available. Like I said, they were supposed to have been out last April according to Nichia's press release. I'm still waiting.

Jeled's 55K mcd is nearly as good as the DS for perhaps 1/3 the price of the CS. And you can get them by the tens of thousands on eBay if you want.

 

[kongfuchicken]

The DS have been available for a while.
You can order them direct from Nichia and they'll ship from Japan.