Which Bulb is Older

[AV8er]

I have a 2 x 150 hqi / 4 x 54 T5 lighting setup... I was having a flickering issue with one of the hqi bulbs a few months ago, so I swapped it for an older phoenix 14,000k hqi I had lying around to bridge the gap. The problem is that they are both phoenix 14,000k hqi bulbs and I can't remember which one I swapped out. The older phoenix needs to be replaced.

I seem to recall it was the bulb on the right, so the best I got is to trust my gut. (Or switch both bulbs).

Absent using a PAR meter (if that would even work), any tricks on how to tell?

 

[mordibv]

U gotta hate that .
Is there any silvering on the bulb ? I would look for the most of that or the gray black color . Those two would possibly indicate the older of the two bulbs .
BTW I am referring to the bulb and not the outer envelope .

HTH