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I'm evaluating the following LED: L130-5080002011001.

It is a 5000K LED with the following range of forward voltage (at 120 mA): min 2.85±0.1 V; max 3.35±0.1 V.

My goal is to drive it with a lower current, about 30/40 mA, with a 5 V voltage source and a limiter resistor.
In this way the declared electrical characteristics given in the datasheet are not reliable anymore (Spectral Power Distribution Characteristics, Light Output Characteristics, Forward Current Characteristics, Radiation Pattern Characteristics, Luminous Flux Bins are all related to the LUXEON 3020 at 120mA, Tj =25°C).

I need to find the working range with my given conditions so I can correctly dimension the driver circuitry.

And how can I characterise the LED with my given conditions (this LED can go up to 240 mA!), at least the Forward Current Characteristics and Electrical Characteristics? Is there a best practice to perform this?

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  • \$\begingroup\$ How accurate characteristics do you actually need? If "should look good to the human eye" is sufficient then just do trial & error with a potentiometer and a bench supply until you find a good series resistance. If you need something more advanced than that, I guess you'll have to build a lab board with a digital pot and some microcontroller. \$\endgroup\$ Commented Aug 22 at 8:37
  • \$\begingroup\$ @Lundin it is a prototyping phase for choosing the right LED. Unfortunately the characteristics can vary for each LED with the same part number because an infinite number of tolerances. \$\endgroup\$ Commented Aug 22 at 8:39
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    \$\begingroup\$ Maybe look into feeding them with a constant current source then, rather than just a 5V. You'll still have to determine the ideal current by tinkering with a bench supply etc though. Or get a better LED with less variations - note that the characteristics can change quite a lot after soldering it. \$\endgroup\$ Commented Aug 22 at 8:43
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    \$\begingroup\$ I have designed a number of (relatively niche) real world LED lighting products. I may be able to provide useful input, BUT I would need to know substantially more about what you are trying to achieve and the context. Even if the project proper is commercially sensitive, LED lighting in general is such a well coverered subject that you could tell us much without touching on confidential areas. See pereblepsis questions to start. || A constant current source as Lundin suggests would be a near essential tool when experimenting - and can be implemented with an LM317 regulator and one resistor. \$\endgroup\$ Commented Aug 22 at 11:54
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    \$\begingroup\$ As Andy notes, you can get some of what you want from the data sheet. There are curves for Vf & luminous output with current. Radiation pattern won't change. || NOT shown and somewhat hard to find in datasheets but available in general literature: As current drops Blue LED colour temperature will become SLIGHTLY bluer. Phosphor output will become SLIGHTLY greener. Overall LED CCT will rise slightly. || Probably: For multiple LEDS wall washing together colour difference from 120 mA and 40 mA side by side would be discernible. Operated in isolation few if any would notice the difference. \$\endgroup\$ Commented Aug 22 at 12:03

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Mike James said:

If the system allows pulse width modulation , this will permit the LED to be driven at the rated 120mA current when its emission should be as specified. Intensity is then controlled by reducing the duty cycle to 33% providing an average 40mA current. Provided the application permits the LED to be flashing rapidly (not being used with rotating machinery e.g. ) this will work.

The above was originally posted as a comment, but is really an answer. Therefore, in accordance with the CC BY-SA 4.0 license and following the approach explained here, it has been moved and reposted here, unchanged and attributed, as an actual answer. The answer has been set to "Community wiki" so that I don't earn any points from votes on this answer, as it isn't mine. (SamGibson)

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And how can I characterise the LED with my given conditions (this LED can go up to 240 mA!), at least the Forward Current Characteristics and Electrical Characteristics?

How problematic would it be to use this graph from the data sheet you linked: -

enter image description here

You may also need to factor-in which "forward voltage bin" your purchases are from: -

enter image description here

So, the graph above looks like it applies to bin W.

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  • \$\begingroup\$ Unfortunately there is no strict bin selection in my case, hence the forward voltage can go from 2.8 V to 3.4 V. Furthermore, the Forward voltage/current characteristics is specialized for a 120mA current, what if I use a 40mA current instead of this one? As @MikeJames said, I could use PWM with my 40mA. However It's not so clear for me how I should proceed. \$\endgroup\$ Commented Aug 22 at 12:50
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    \$\begingroup\$ @Crazycircuit look at my first graph and choose 40 mA on the vertical axis and move along to the curve. Then project downwards to find the typical volt drop (maybe 2.83 volts) but, this only works if you had bought W binned LEDs. If you haven't then test each LED at 40 mA and categorize them yourself in terms of what resistance is needed to get 40 mA on a 5 volt supply. \$\endgroup\$ Commented Aug 22 at 13:44
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    \$\begingroup\$ @MikeJames - Hi, As explained by another moderator after your first comment (now deleted), your comments are really an answer and should be posted as such (please see the SE commenting policy for what is allowed in comments). Therefore I moved your expanded comment from today, into an answer. Please avoid answering questions in comments. Thanks for your cooperation with this. \$\endgroup\$ Commented Aug 26 at 12:18

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