Are these numbers at the substrate?Good question! From the PAR meter rules:
"What Do My Results Mean?
There is no universally accepted interpretation of PAR values for aquaria. Here are two proposed scales for comparison. All values are given in micromoles per square meter per second.
20-40 low light
40-100 medium light
100+ high light
40-70 low light
70-150 medium light
150-300 high light
300-600 very high light
By reporting your results and comparing them to others, you can help to develop realistic guidelines for light levels in planted tanks."
From the information we've gathered to date, I tend to agree with the first scale. You can definitely grow low-light plants with less than 40 umol.
I notice lots of people having reduced PAR deeper in the tank. I measured my PAR and found almost no difference. Done with a Seneye which compared to the Apogee gave almost the same readings.PAR VALUES MEASURED AT WATER LEVEL: 201
PAR VALUES AT MIDDLE: 120
PAR VALUES MEASURED AT SUBSTRATE: 82
Agreed. Would need to know this to be 100% sure, but even so 45 seems like a very low value for 220w.But what was the PAR of the 220 to begin with? Maybe lots of green, no red or blue? Someone on a Dutch forum stated that Philips t5ho had only 5% reduced PAR over a few years...