diff --git a/src/drivers/nl_sm2135eh.c b/src/drivers/nl_sm2135eh.c
index da0f95e..6730251 100644
--- a/src/drivers/nl_sm2135eh.c
+++ b/src/drivers/nl_sm2135eh.c
@@ -7,6 +7,7 @@
 #define SM_ADDR_CURRENT 0xC0u
 #define SM_ADDR_WY      0xC5u
 #define SM_CHANNEL_WY   0x80u /* channel select bit 7: 0 = RGB, 1 = WY */
+#define SM_CHANNEL_STBY 0x20u /* standby bit 5: powers the outputs down */
 
 extern void delay_us(unsigned int us); /* provided by libwlan.a */
 
@@ -76,7 +77,15 @@ void nl_sm2135eh_set(const uint8_t ch[NL_CH_COUNT])
     s_have_last = true;
 
     if (!white) {
-        uint8_t d[6] = {SM_ADDR_CURRENT, s_current, 0x00, ch[NL_CH_B], ch[NL_CH_G], ch[NL_CH_R]};
+        /* All channels dark: put the driver into standby instead of just writing zero duty.
+           Without bit 5 the chip stays active and leaks enough current to keep the lamp
+           faintly glowing - measured on a migrated GU10 RGB, 2026-09-13. The old QConnex
+           firmware had this logic but left it commented out (qcl_lamp.c), which is why the
+           behaviour was inherited. Lamps driven straight from PWM pins (G95, the CW variants)
+           are unaffected. Turning back on writes 0x00 or SM_CHANNEL_WY here and clears it. */
+        bool dark = !ch[NL_CH_R] && !ch[NL_CH_G] && !ch[NL_CH_B];
+        uint8_t chan = dark ? SM_CHANNEL_STBY : 0x00u;
+        uint8_t d[6] = {SM_ADDR_CURRENT, s_current, chan, ch[NL_CH_B], ch[NL_CH_G], ch[NL_CH_R]};
         sm_send(d, 6);
     } else {
         uint8_t h[3] = {SM_ADDR_CURRENT, s_current, SM_CHANNEL_WY};