Turns the Mac Studio's front power LED into a load meter. It pulses while the machine works, brighter the more power it draws, and holds its normal glow when idle.
board power (SMC PD0R) LED
idle, < 50 W ─▶ steady, stock brightness
50 W ─▶ slow pulse, dim peak
60 W ─▶ pulse, peak ~75%
180 W and up ─▶ pulse, full peak
Tested on one machine: a Mac Studio with M5 Ultra, macOS 27. Other Apple Silicon Macs may name their keys differently. Run sudo ./led-probe.sh to find out.
make
sudo ./studio-ledIt needs root because every SMC write does. Ctrl-C, SIGTERM, or a dropped ssh session puts the LED back the way it found it.
| Flag | Default | What it does |
|---|---|---|
-w WATTS |
50 | board power that counts as working |
-F WATTS |
180 | board power for a full-brightness peak |
-p SECONDS |
2.4 | one breath |
-l HEX |
0000 | the dim end of each breath |
-f PATH |
none | also count as working while this path exists (a lock dir your long jobs hold) |
-k KEY |
LSLN | the brightness key to drive |
The 50 W default is a guess, since the idle draw hasn't been measured yet. Check yours with ./smcdump PD0R before you rely on it.
make
sudo make install # /usr/local/libexec/studio-led + /Library/LaunchDaemons/local.studio-led.plist
tail -1 /var/log/studio-led.logsudo make uninstall stops it, which restores the LED, and removes both files. It has to be a LaunchDaemon rather than a LaunchAgent, because a LaunchAgent runs as your user and SMC writes need root. The binary is copied to a root-owned path, so the daemon never runs a file your account can edit. To pass flags, add them to ProgramArguments in local.studio-led.plist before you install.
Apple documents none of this. These are the LS* SMC keys on the M5 Ultra Studio and what writing them did to the LED:
| Key | Stock | Write | LED |
|---|---|---|---|
LSLN |
ffff |
0000...ffff |
smooth dimmer; 0000 is dim, not off |
LS0S |
b366 |
0000 |
very dim |
LS0C |
ffff |
0000 |
dim |
LS0P |
66b3 |
0000 |
bright |
LSOF, LSLB, LSLF |
no visible change | ||
LS1* |
little or no change (probably a second channel the Studio doesn't wire up) |
Some writes push the LED brighter than stock, but which key does it isn't pinned down yet. LS0P and LS0S are byte-swapped copies of each other, so they probably work as a pair. Keys such as LSOO and LSSB fail on read. They drove the sleep light on Intel Macs, and they may be write-only here.
| File | What it does |
|---|---|
studio-led |
the daemon |
smcdump [prefix] |
prints every SMC key with that prefix, with its type and value; no root |
smcwrite KEY HEX |
writes raw bytes to one key and reads it back; root |
led-probe.sh |
steps through the LS* keys one at a time and restores each one; root |
smc.c and smc.h come from mactop (MIT).