TLDR version: if you have a large fixture (lots of LEDs) turn them down and hang them closer. If you have a small fixture, hang it higher for better (more even) canopy coverage.
We compared the Photone Ap against a $1600 hand-held spectrometer (Lighting Passport) and as long as you covered the phone camera with a piece of white paper to diffuse the light, it was quite accurate.
Lifting the light
Pros: Easy to do, easy to reference (by distance from plant canopy); can give a fairly uniform coverage of light over the canopy
Cons: Wastes energy and light; doesn't reduce heat in the grow area; may run out of head height; usually reduces penetration due to wasted light and wall losses
Reducing intensity
Pros: Increases efficiency of the LEDs; reduces energy usage and heat; usually increases penetration by increasing the angles of available light that can penetrate through and under the foliage; increases life of LEDs
Cons: Lights must be constantly adjusted for growing plants (easier for plants to grow into the LEDs); reduces light footprint, which can create uneven canopy lighting if the fixture is small and the canopy area is large
Light meters are great, but every plant is different and some respond better to higher levels of light than others (sativas vs indicas for example). For that reason, a simple Watt meter (also known as an energy cost meter or wall meter) can be invaluable for setting up your lights by simply turning them down to a suitable wattage until your plants are happy, and using that wattage reading as a reference for each time you need to turn the lights up and down.
