Notices by teddy (tedyapo@fosstodon.org)

@gorplop opaque black acrylic cover. zero lux counts with the LED off, but i do measure the dark current just in case

@gorplop atm, it's using a carefully calibrated VEML7700 ambient light sensor IC, making sure to stay in the linear region. i have a 7-decade photodiode/TIA meter in the works

but why?, you ask.

LEDs efficiency is a strong function of driving current. e.g., here's the measured relative efficiency of a "3W" LED. the LED is rated for 350 mA forward current, but if you drive it that hard, efficiency drops by 40%.

if you've heard of the dubai lamp, this is how they did it. this particular LED is most efficient when driven around 35 mA, 1/10 of its rated current (which is set by thermal constraints)

i'm developing an ultra-efficient LED driver, so i need this data

in front, there's an optical rail made from 2020 extrusion and 3D printed parts. the fan isn't needed for testing this 5mm LED, obvs, but it comes in handy with the bigger ones. a black acrylic cover slips over the rail in use to block ambient light

i lost something like this a couple years ago, so had to build a new one for an upcoming project. it's an LED/LD tester that can record forward voltage and relative optical flux from devices under currents from 1uA to 1A. 16-bit differential ADCs kelvin-connected thru a relay switching network. 0.1% FS accuracy in 1mA, 10mA, 100mA, and 1A ranges