I'm just wondering if anyone can help...I have some old Philips lamps one has a date code 0M this is the oldest one of the lot 2 others i have are slightly newer they the codes on these are 3C and 3E Some of my newer ones have 7J just wondering if anyone can explain how these codes work?
thanks

The Philips letter-digit and v.v. date coding format is as follows:

early 60s till December 1969, 1980s, 2000s: letter-digit format
1970s, 1990s, 2010s: digit-letter format

digit = last digit of the year. E.g. 4 = 1964, 1974, 1984 etc
letter = month: A= January, B= February ... M=December. The letter I is excluded.

So 0M could be December 1970, December 1990. In your case of an old lamp, it's probably December 1970.
3C is March 1993 or 1973, 3E is May 1993 or 1973  and 7J is September 1997 or 1977.

Ideal thanks for that. I would of thought by the lamp end caps being the design they are that the 0M lamp i have is more like december 1960 Thanks for your help anyway i will know this for future use!

Ah thanks for this, I knew how the date codes worked but not that letter I is excluded so I was confused why one of my tubes had M7 on it. 1960s design so must be December 1967

I'm not sure when Philips adopted this production code format. The earliest examples I have seen date back to 1964. But maybe it was introduced already before that year?

This sounds about right.  The Philips specs which indicate the structure of the previous dot-dash system only disclose code combinations as far as December 1963, so by January 1964 the new system would have had to take over.  However it is possible that the new system was also implemented in some factories before Jan 64.

I have a light here I would appreciate is any one could tell me it has c1 which I believe is March 1991

I have two 135W Philips sox lamps whith the code 7H on.
I can't find any date-information on the internet about them.

See here. 7H is August 1977/1997/2017 - you will have to decide the decade based on the lamp design, if you think thay're very new or very old lamps.

I don't know anything about Sox lamp design. I got my very first Sox lamp last autumn. But I guess it is probably 2017.

I don't think this date code is applied to all Philips luminaires.For example, the date code of Philips LEDs is 4 digits, and there is no regularity. Philips HPI-T (conventional), including China, uses the date format of "Mfg:yyyy/mm/dd".

  Here in the US philip starts in 1980s format
  But from 1984 to 1987 will have tale tale sign
   Of philip westinghouse.   Then philip etch
   And date code.  Same for 1990s with digit
  Swap.  Lamp started alto series in 1998
   Carries onwards 2000 lamps will have letter
    E for EPACT compliance.  2010 time period
  Is  dead giveaway with green endcaps
    And lamp started containing mercury
   Wording.  Then  2020 philip undergoing
     Lamp plant closing process.   July 15 2021
    Ended long lamp production of HO here in the
     US.   Now lamp production carries on in Poland
    And India  with EU style endcaps on slimelines
     And there in process setting up the HO lines as
     Philip over produce the HO lamps here in the US.
      And T8 are from Poland.  So that will give u better
      Clue how to Date US Philips lamps

        In 1970s sox lamp in the US is norelco ones
   This lasted until philip bought out westinghouse
      Change to  philips fallow EU date coding

       US hid lamps philip-westinghouse till 1987
   And most lamps in this perod is the westy BT
 Shape lamps.  1990s philips ED shape glass
  Came out this carries over unti bath plant lamp
    Closure 2008  all our hid lamps comng from
    Poland and China
     

Here’s a question?, why did they even use codes???
What was up with just printing 15/07/64, or 07/15/64 for US lamps, why go to to all the bother of breaking dates up into codes?

Could have been lack of space on the etch in the early days 

Or maybe it was just to confuse the masses, i.e. us 

July 15 2021   Is when last American fluorescent produced
Here in the US.  And Exit the North Amarican Manufactureing
  The last Lamp they made for that day was HO 8 foot 110 watt
   Fluorescent.   Whaf make a end period though years
  Of 1983 to july 2021 date codes date codes on American
  Philips fluorescent tubes.   But this date code will carry on
   With poland and India tubes. This make a new start line
  For tubes comminng into the US.   But we have older poland
   Lamps  such as CFLs and EU Ts  and some of there hid lamps.

    So finding a August 2021 North American tubes not going to happen as there is no such tubes

   Philip in the US bought out few lamps plant in the late 1960s or 70s time time frame such as Itt and Champion lamp plant.  But there was bit of a problem philip could not Use there own name
 Because it would create confusion with Philco radio.  So philip
Had to rename the company under North American electric lamp company
So they took all that wording Nor as in north and E as electric L as in lamp and CO company and that how Norelco got it name.  Until 1982
Philip bought out Philco radio.  And then They bought westinghouse Lamp Division in 1983.  So any philip lamps that were made in the US
Before philips was sold under norelco and yes that included sox lamps for US market.   So it bit easier dating US philips lamps because there lot of changes in manufactureing in each of it decades. That what I am pointing out to.