I’m sure most of us know about the date code that Philips has used on their lamps since the 1960s. The code consists of a number which indicates the last digit of the year, and a letter which indicates the month, starting with A = January and skipping I, and the ordering of the number and letter reverses every decade.

This is one of the most well-known and easiest lamp date codes to decode, but I think where most of us become stuck (myself included) is with the ordering of the number and letter. I noticed that the position of the number happens to be even (2) for the even decades and odd (1) for the odd decades (or maybe that is intentional). The position is odd for the 1970s, 1990s, etc. and even for the 1980s, 2000s, etc..

So behold my mnemonic device for remembering this:

Position Odd, Decade Odd
Position Even, Decade Even

I hope you this helps with remembering these date codes. It will certainly help me.