The standard measure that quantifies the energy available for photosynthesis is "Photosynthetic Active Radiation" (aka "Photosynthetic Available Radiation") or PAR. It accounts with equal weight for all the output a light source emits in the wavelength range between 400 and 700 nm. PAR also differs from the lumen in the fact that it is not a direct measure of energy. It is expressed in "number of photons per second". The reason for expressing PAR in number of photons instead of energy units is that the photosynthesis reaction takes place when a photon is absorbed by the plant; no matter what the photon's wavelength is (provided it lies in the range between 400 and 700 nm). In other words if a given number of blue photons is absorbed by a plant, the amount of photosynthesis that takes place is exactly the same as when the same number of red photons is absorbed. This is why it is so important to get the spectral output of a bulb before deciding if is a 'good plant light'. You may need to add/mix bulbs to get a lighting that has good visual effects for the human eye and proper light for plants because 'plant bulbs' tend to be purplish. There is an additional term called "Photosynthetic Usable Radiation" or PUR which takes in to account blue and red light only.

I don't understand why people insist on distinguishing between lamps on the basis of their color temperature. No lamp renders color correctly or looks natural unless its Color Rendering Index (CRI) rating is very high. When CRI is over 90 the color temperature shouldn't make much difference; colors rendered accurately will always look about the same regardless of the Kelvin rating. Many bulbs render red and orange colors poorly and give you a look with very flat color contrasts. Other bulbs produce a lot of green light and don't render either blue or red very well at all.

CRI or Color Rendering Index is an indication of how close the light is to daylight (full spectrum) on a scale from 0 to 100 with respect to how it makes objects appear. In the case of the Philips PL-L 950, the CRI is 92, so it has pretty good color rendering properties. Two bulbs with the same Kelvin temperature but different CRI ratings can produce very different appearances. Compare a 5000K that has an 80-something CRI with a 5000K that has a 90-something CRI. The 80 CRI bulb is very bright, but it renders greens with a distinct yellow cast. The 90 CRI bulb is dim, but it renders rich colors across the whole spectrum.

Whether or not a bulb looks "natural" to you is totally subjective. It depends in part on what you're used to. If you only see the world under cool white fluorescents then that is probably what looks natural to you. If you live somewhere with frequently hazy or overcast skies then you may be accustomed to "natural" light having a color temperature near 7000K. If you live somewhere with clear skies and infrequent cloudy days then your natural light might have a color temperature closer to 5000K. If you are used to north skylight then maybe a color temperature close to 10,000K seems more natural. In any case of actual natural light the light will render colors pretty well. That is usually not the case for fluorescent lamps with a high Kelvin temperature rating. If you want a high K lamp that does render colors accurately then you might try finding the Philips C75. It has a 7500K color temp and a 90+ CRI. It could be hard to find and a bit pricey. 

Plants will grow with ordinary bulbs as they tend to have both some blue and red emissions. The problem is that they also have wavelengths between 500 and 600nm, which algae likes. Green algae and green plants use the same pigments for photosynthesis (chlorophyll a/b & carotenoids). So, light that helps one helps the other. The algae that are different are the blue-green algae (cyanobacteria), which contain Phycocyanin and absorb light heavily in the low 600nm (orange-red), which is unfortunately present in most standard fluorescents. In the planted aquarium artificial light should ideally peak (or be stronger) in the red area of the spectrum. The tanks’ appearance can be compensated (balanced) with blue light and some green light for brightness to the human eye. Strong blue light will cause plant growth to be more compact and bushy and will also tend to promote algae growth. So remember to balance 2/3 red to 1/3 blue light emissions.