What do you think about UHE LEDs?
It is advertised as an efficient LED, achieving 190lm/W compared to SST40 150lm/W.
What do you think about it in general?
I will be reviewing Nitecore HC65 headlamp, which uses UHE LEDs, and I will write about my thoughts, but meanwhile I would like to know what are your thoughts.
I am skeptical of this emitter for a couple of reasons.
- Does Nitecore specify the current input for the 190lm/W figure? All LEDs are increasingly efficient at lower power densities; consequently one can hack the efficiency metric by distributing power across multiple LEDs (which Nitecore seems to be doing) or using LEDs with a large die.
To avoid these hacks, one way to measure efficiency of an LED is to look at the limiting efficiency as current approaches zero (i.e., the right-derivative of the output-power plot at zero). This is because no matter how one tries to distribute power, the resulting efficiency can never exceed this limit. In this case the SST40 can do more than 217lm/W at 0.2A, per this test. That’s more than the 150lm/W cited, and more than Nitecore’s 190lm/W.
- Also Nitecore’s LEDs are generally very green, which helps tremendously with efficacy. Note here that lm/W is actually a measure of efficacy, while efficiency is a unitless quantity. For light with the same spectrum, e.g., different drive levels for the same LED, the efficiency and efficacy are proportional and thus often used interchangeably for comparison purposes. But since we are comparing different LEDs, the distinction must be made.
To illustrate: a perfectly efficient source (converting 100% of electrical energy into light) of white light can achieve an efficacy of around 300lm/W, depending on the definition of white. Maybe a bit higher if one allows for lower CRI and more tint deviation. However, a green light at 555nm can have an efficacy of up to 683lm/W. The more green a white light is, the closer it can approach this higher efficacy, without being more power-efficient.
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3 Thanks
Has anyone here sharp macro images of these emitters? They look like some sort of CSP style ones, but in an odd shape.
Where datasheet?
I think we will never see a real datasheet for these, as with Chinese emitters in most cases…
Seems to be a top secret.
Yeap. Efficiency probably because of matrix of 8 in parallel.