Anybody heard of Nanolight?

I once calculated the maximum efficiency for a cool white spectrum (from an XP-G spec) to 320 lm/W.

Taking into account the conversion losses in the phosphor (blue photons of high energy are converted to yellow lower energy ones), the theoretical maximum with that technology should be around 260 lm/W, i.e. max 80% efficiency.

These data depend on LED spectral data, and I took the numbers from the graph "by hand", so it's not that precise.

I wish I had more precise spectral data, and of more tints...

DrJones, thanks for jumping in on that, but can you tell us something about thermal efficiency? How much heat would these LEDs produce at 12W?

Here’s the simple truth… White LED’s (for the most part) are really Royal Blue LEDs which are passed through a phosphor to convert the blue light into white light. As with ANY conversion, there is loss involved in the conversion.

So, lets start with a Cree Royal Blue LED like the XT-E.
Since, in this application, we’re talking about fairly light drive-currents, I’ll use the minimum published (most efficient) (350mA) numbers in this example.

Vf at 350mA: 2.85
Current: 350mA
That gives us 0.9975 Watts of input power.

Even the highest bin only has 550mW of output power (light) which means that 447.5mW of heat is generated.

The three bins of Royal-Blue output 500, 525 and 550mW respectively. It’s fairly safe to assume that those same power levels are in the White LED’s with a phosphor on top.

So, even the highest rated Royal-Blue LED is only 55% efficient at converting electricity into light. The phosphor on top will further decrease that efficiency (quite substancially, in fact). It’s a fairly safe bet that AT BEST, a white LED is about 35% efficient at making light from electricity. Hence, 12Watts of LED’s will probably produce about 7.8 Watts of heat.

And that’s at VERY low drive strengths. At higher currents, it get’s worse and fast.

At 1500mA (full drive), the same XT-e now figures like this:
Vf @ 1500mA: 3.37V
Current: 1500mA
That gives us 5.055 Watts of input power.

But output has only gone up by about 310%, so the highest binned Royal-Blue is putting out 1705mW of light.

Now the efficiency is calculated as: 1.705/5.055 = 33.7% efficient.
Add the phosphor on top, and you’re going to be darn lucky to be left with 25% light and 75% heat.
So an XT-E driven at 1500mA will generate about 3.8 Watts of Heat from about 5 Watts of power.


Thanks Pilot. :)

But you did once post that you calculate with 100% transformation to energy for safety margins, or is my mind playing games with me?

Nope, I did post that, and we still do. It’s a safety thing. It gives us some automatic design margin. Why calculate out 25% and then add it right back as typical design safety margin? Two unnecessary steps…


@NightCrawl: Assuming my calculated 320lm/W and their 133lm/W is correct, the efficiency would be 133/320=~40, thus ~60*12W=7.2W heat.

Assuming 12W/3V/33=120mA per LED - Maybe… But indeed 40% sounds quite high.

For an ideal 5800 K black-body radiator, truncated to 400–700 nm the Luminous Efficacy of RADIATION is 251 lm/W. This is determined only by definitions of the spectral response of the human eye.

But it’s essential not to get confused between OPTICAL watts and ELECTRICAL watts.

Luminous Efficacy of RADIATION refers only to how the TOTAL radiation within 400–700 nm, coming from a light source can be detected as visible light - so it’s based on OPTICAL watts. It totally ignores heat radiation above 700nm and totally ignores heat CONDUCTED from the LED.

When BLFers talk about how many Lumens a white LED delivers, we’re interested electrical efficacy - how many ELECTRICAL watts are converted to Lumens. So we need to add in the efficacy of converting electrical watts to Blue light watts, then converting blue light watts to yellow light watts.

There are so many assumptions needed here, I decided a practical test was the best way to get an accurate figure of how much heat is CONDUCTED from real world LEDs. My tests came up with the figures others have quoted - about 75% of the electrical input watts are converted to heat watts.

CPF thread

I really like that they use the external shell as the heatsink, TONS of surface area!

Even if it pumped out the lumens that a normal 60 watt lightbulb would produce at 7watts power usage that in itself is a great saving of money, I think their next generation does have heat protection and will self dim, I don't believe this no heat thing, especially since the experience with larger flashlights that make ALOT of light but get very warm very quickly

Bump for great justice

Exactly. Neither do they care to provide any technical specs as to what LEDs they use.

Looks like any other LED bulb to me and they sure don’t cost $30 or more.

Nothing extraordinary. Just another overpriced LED bulb with crappy CRI.