Another interpretation: "from evening until morning" (Exodus 27:21). You have no service that is valid [stretching] from evening until morning except this one alone. The Sages estimated three and a half [log] for the menorah, half a log for each and every lamp, from nightfall until daybreak. There are those who say the measure was reckoned from above downward [from the longest summer nights], for there is no stinginess in a place of wealth. And there are those who say the measure was reckoned from below upward [from the shortest nights], for the Torah spares the money of Israel.
The Half-Log of Oil and How the Torah Spares Israel's Money
Yalkut Shimoni on Torah 378:12
דָּבָר אַחֵר, מֵעֶרֶב עַד בֹּקֶר. אֵין לְךָ עֲבֹדָה שֶׁכְּשֵׁרָה מֵעֶרֶב וְעַד בֹּקֶר אֶלָּא זוֹ בִּלְבַד, וְשִׁעֲרוּ חֲכָמִים שְׁלֹשָׁה וּמֶחֱצָה לַמְּנוֹרָה, חֲצִי לוֹג לְכָל נֵר וְנֵר, מֵאוֹרְתָא וְעַד צַפְרָא. אִכָּא דְּאָמְרֵי, מִלְּמַעְלָה לְמַטָּה שִׁעוּר, אֵין עֲנִיּוּת בִּמְקוֹם עֲשִׁירוּת, וְאִכָּא דְּאָמְרֵי, מִמַּטָּה לְמַעְלָה שִׁעוּר, הַתּוֹרָה חָסָה עַל מָמוֹנָם שֶׁל יִשְׂרָאֵל.