In هُوَ اللَّهُ, the word preceding Allāh ends with fatḥah, so the lām of the Divine Name is pronounced heavily. The trigger is the preceding vowel, not an emotional or honorific choice.
In الصَّمَدُ, the definite-article lām assimilates into ṣād; this is the sun-letter rule. The two decisions concern different features: heavy/light lām in the Divine Name versus pronounced/assimilated lām in the definite article.
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Al-Ikhlāṣ: two different lām decisions
Applied Tajwīd Diagnostics: Four Short Sūrahs
In هُوَ اللَّهُ, the word preceding Allāh ends with fatḥah, so the lām of the Divine Name is pronounced heavily. The trigger is the preceding vowel, not an emotional or honorific choice.
In الصَّمَدُ, the definite-article lām assimilates into ṣād; this is the sun-letter rule. The two decisions concern different features: heavy/light lām in the Divine Name versus pronounced/assimilated lām in the definite article.