...In conclusion, if you set 2 PAR 38 15x1W LED with 60 degree lens at height of 30" from the surface of your substrate it is still consider high light range of planted tank and you should use CO2.
The Bulb Product info says:
• Includes twelve 1 watt Cree LED emitters
• Optimum PAR 65K Daylight emitters
• 95 lumens per watt
• 8 inch x 8 inch light spread at 8-12 inches from aquarium
• Simple operations as it fits into a standard household E26/E27 incandescent socket
• The PAR 38 LED is 5 inches wide by 4 inches with a light spread of about 12-13 inches when light is mounted 8-10" above water surface
• Focused Lumen Output
So, now I wonder is I really only need 1 PAR38 bulb?
The tank is only 15 deep and will house low light plants. If I go this route I'll use a track light pendant to mount the light so height adjustment or even adding a 2nd pendant is a non issue.