diff --git a/libs/spandsp/src/t42.c b/libs/spandsp/src/t42.c
index fc90ddba63..6117cd3f19 100644
--- a/libs/spandsp/src/t42.c
+++ b/libs/spandsp/src/t42.c
@@ -102,23 +102,23 @@ typedef struct
 
 static const illuminant_t illuminants[] =
 {
-    {"\0D50",  "CIE D50/2°",   96.422f, 100.000f,  82.521f},
+    {"\0D50",  "CIE D50/2°",   96.422f, 100.000f,  82.521f},    /* Horizon Light. ICC profile PCS */
     {"",       "CIE D50/10°",  96.720f, 100.000f,  81.427f},
-    {"",       "CIE D55/2°",   95.682f, 100.000f,  92.149f},
+    {"",       "CIE D55/2°",   95.682f, 100.000f,  92.149f},    /* Mid-morning/mid-afternoon daylight */
     {"",       "CIE D55/10°",  95.799f, 100.000f,  90.926f},
-    {"\0D65",  "CIE D65/2°",   95.047f, 100.000f, 108.883f},
+    {"\0D65",  "CIE D65/2°",   95.047f, 100.000f, 108.883f},    /* Noon daylight, television, sRGB color space */
     {"",       "CIE D65/10°",  94.811f, 100.000f, 107.304f},
-    {"\0D75",  "CIE D75/2°",   94.972f, 100.000f, 122.638f},
+    {"\0D75",  "CIE D75/2°",   94.972f, 100.000f, 122.638f},    /* North sky daylight */
     {"",       "CIE D75/10°",  94.416f, 100.000f, 120.641f},
-    {"\0\0F2", "F02/2°",       99.186f, 100.000f,  67.393f},
+    {"\0\0F2", "F02/2°",       99.186f, 100.000f,  67.393f},    /* Cool white fluorescent */
     {"",       "F02/10°",     103.279f, 100.000f,  69.027f},
-    {"\0\0F7", "F07/2°",       95.041f, 100.000f, 108.747f},
+    {"\0\0F7", "F07/2°",       95.041f, 100.000f, 108.747f},    /* D65 simulator, daylight simulator */
     {"",       "F07/10°",      95.792f, 100.000f, 107.686f},
-    {"\0F11",  "F11/2°",      100.962f, 100.000f,  64.350f},
+    {"\0F11",  "F11/2°",      100.962f, 100.000f,  64.350f},    /* Philips TL84, Ultralume 40 */
     {"",       "F11/10°",     103.863f, 100.000f,  65.607f},
-    {"\0\0SA", "A/2°",        109.850f, 100.000f,  35.585f},
+    {"\0\0SA", "A/2°",        109.850f, 100.000f,  35.585f},    /* Incandescent/tungsten */
     {"",       "A/10°",       111.144f, 100.000f,  35.200f},
-    {"\0\0SC", "C/2°",         98.074f, 100.000f, 118.232f},
+    {"\0\0SC", "C/2°",         98.074f, 100.000f, 118.232f},    /* {obsolete} average/north sky daylight */
     {"",       "C/10°",        97.285f, 100.000f, 116.145f},
     {"",       "",              0.000f,   0.000f,   0.000f}
 };