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About LED's power ratings

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qwertyqwq

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hi all

currently im building a circuit using series connected leds on aluminium pcb board. for that purpose i have some questions about leds.

on my circuit i will use 18v smd 2835 led chips. max amouth of current on each led will not exceed 27,27mA. on so on i need at least 0.5w led chips. But what if i solder 1W 18V led instead of 0.5W 18V led's ??

As wattage increased it must be much more long life but what happens when 27,27mA of current flows through 1W leds ? Will brighness decrease ? Or when i dimm the current less then from 27mA , what will happens on 1W led.

As you can see i have so much miss understoods about leds wattages , please explain more details.

Thanks
 
Do you have a link to these 18V LEDs?

Mike.
Edit, for most LEDs running at half current will mean half brightness - so should be the same as 0.5W but cooler.
 
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Do you have a link to these 18V LEDs?

Mike.
Edit, for most LEDs running at half current will mean half brightness - so should be the same as 0.5W but cooler.
Great its exactly what i have thought , thanks a lot

Actually there is no such a link for that , it s belongs to Aliexpress web page so , unfortunately there is no such an information about leds or produced by whom.

Im thinking that so you are saying , for different type of wattage leds , which on this case 0.5-1W leds , will same lumen(brightness) rating for equal amout of current flowing on them , right ?
 
The only datasheet I could find is here. If you look at the graph on page 18 the luminosity is directly proportional to the forward current.

Mike.
 
The graph shows that the LEDs are slightly more efficient at half current, but it's only a slight effect, but the light will be more than half the maximum at half current.

Also at half current, the voltage will be a bit less than the voltage at full current, so the power will be a bit less than half.

Running at less than half power will extend the life a lot.

explains about running LEDs at lower powers.
 
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Yes, Luminance is radiometric flux corrected for eye wavelength response.

But flux, a component of Luminance, is dependent on the ratio of heat/light
produced by LED, and that ratio is not linear.

Also LED wavelength versus current is not linear, hence affects apparent brightness.

But the above are radiometric.

Eye affects and model inconsistencies well described here -


Other -



Regards, Dana.
 
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We can see in very bright sunlight and also see in very dim moonlight.
Disregarding the brightness adjustment by the iris in an eye I think brightness is logarithmic to the LED current.
Double the current is only a little brighter, 10 times the current appears twice as bright.
 
But the question is, will a 1W LED run at ½W be the same brightness as a ½W LED run at ½W?

Mike.
 
LEDs have a shift in spectral response with current, hence illuminance also changes,
so apparent brightness changes.

Luminous flux is linearity looks like below over most of LED current range -

1648113339481.png


There are other considerations however some of these minor effects.


Regards, Dana.
 
A poor quality LED is dim and a high quality LED is bright when their currents are the same.
Some LED manufacturers test then throw away LEDs that do not meet their specs then scroungers pick the defective LEDs and sell them on ebay or on the other online places "over there".

A LED that has its light focused into a narrow beam is brighter that a LED with a wide angle beam.
 
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