When Did the Burning of the Ner Tamid become Perpetual?

Question

In Parshat Tetzaveh (Exodus 27:20-21) the first mention of the term "ner tamid" in the Torah appears. I had always thought of the ner tamid as the "eternal" or "perpetual" light. Yet it is clearly stated in this passage that the ner tamid shall burn from evening to morning.

20 וְאַתָּ֞ה תְּצַוֶּ֣ה ׀ אֶת־בְּנֵ֣י יִשְׂרָאֵ֗ל וְיִקְח֨וּ אֵלֶ֜יךָ שֶׁ֣מֶן זַ֥יִת זָ֛ךְ כָּתִ֖ית לַמָּא֑וֹר לְהַעֲלֹ֥ת נֵ֖ר תָּמִֽיד׃

You shall further instruct the Israelites to bring you clear oil of beaten olives for lighting, for kindling lamps regularly.

21 בְּאֹ֣הֶל מוֹעֵד֩ מִח֨וּץ לַפָּרֹ֜כֶת אֲשֶׁ֣ר עַל־הָעֵדֻ֗ת יַעֲרֹךְ֩ אֹת֨וֹ אַהֲרֹ֧ן וּבָנָ֛יו מֵעֶ֥רֶב עַד־בֹּ֖קֶר לִפְנֵ֣י יְהוָ֑ה חֻקַּ֤ת עוֹלָם֙ לְדֹ֣רֹתָ֔ם מֵאֵ֖ת בְּנֵ֥י יִשְׂרָאֵֽל׃ (ס)

Aaron and his sons shall set them up in the Tent of Meeting, outside the curtain which is over [the Ark of] the Pact, [to burn] from evening to morning before the LORD. It shall be a due from the Israelites for all time, throughout the ages.

In the synagogues I've attended the light is kept on perpetually.

1. If "ner tamid" does not mean perpetual or eternal light, what is the correct translation?
2. When did this change in keeping the light on from evening to morning to perpetually occur?
3. Was there some event or reason for the change?

TIA...ron

Answer 1

Exodus 27:20

20 And you shall command the children of Israel, and they shall take to you pure olive oil, crushed for lighting, to kindle the lamps continually.

Rashi explains that Tamid means continually, that is every day. This is similar to the korbon tamid which is brought every day at the appropriate time.

continually: Heb. תָּמִיד. [Since it burns] every night, it is called תָּמִיד, as you say: “a continual burnt offering” (עֹלַת תָּמִיד)” (Exod. 29:42, Num. 28:6), [which is called “continual”] although it is [offered up] only from day to day. Similarly, concerning the flat pan meal offering [of the Kohen Gadol, the word] תָּמִיד is mentioned although it is [offered up] only half in the morning and [the other] half in the evening. [The word] תָּמִיד mentioned concerning the showbread (Exod. 25:30), however, [literally] means from Sabbath to Sabbath [i.e., continually].

Jewish Virtual Library explains this as a remembrance of the menorah as well as the incense altar.

It is often associated with the menorah, the seven-branched lamp stand which stood in front of the Temple in Jerusalem. It is also associated with the continuously-burning incense altar which stood in front of the ark (see First Kings, chapter 6). Our sages interpreted the Ner Tamid as a symbol of God's eternal and imminent Presence in our communities and in our lives.

Chabad.org says that the custom is referenced as a universal custom in the fifteenth century.

Although the origins of this custom have been lost, the anonymous work known as the Kol Bo (published in the late 15th century) records that it was a universal custom in his days. He writes that the reason for the light is to give honor to the Divine Presence that rests wherever a quorum of Jews gather to pray.