Having decided to upgrade my lighting from T8 to T5 I treated myself to a second-hand 120cm T5 Arcadia Luminaire off eBay. It came with used marine tubes so I ditched those as they aren't designed for planted tanks. Next was to purchase four 54 watt T5 tubes for it. Looking at the £15 or more for a single tube from online aquarium shops, I decided to look elsewhere. The problem with using normal tubes is that they are designed for lighting rooms and not fish tanks so a bit of trial and error was required to get the best results. There are lots of reports on what wavelengths are best for plants but nearly all this data comes from terrestrial plants and not aquatic ones. I'm of the opinion that as long as you have a well balanced spectrum with plenty of red, green and blue wavelengths then the plants will grow fine.

Armed with my credit card I went and visited my favourite online light shop Lamp Specs and purchased a range of fluorescent tubes.



Osram Lumilux 1149mm T5 840 Fluorescent Tube 54W
Osram Lumilux 1149mm T5 865 Fluorescent Tube 54W
Osram Lumilux 1149mm T5 880 Skywhite Fluorescent Tube 54W
Philips de Luxe Pro T5 965 Fluorescent Tube 54W (Known as Colour 96 on Lamp Specs website)
Sylvania Grolux 1149mm T5 54W

Before I go into tube comparisons I'll explain a bit about the numbering on the tubes.
CRI or Colour Rendering Index describes how a light source makes the colour of an object appear to human eyes and how well subtle variations in colour shades are revealed. It is measured on a scale of 0 to 100 where 100 is best.
Kelvin (K) or Colour Temperature is a measurement in degrees Kelvin that indicates the hue of a specific type of light source. Normal daylight colour is around 6,000K. Reds have a lower K value and blues have a higher K value.

So if you look at my first bulb it has a number of 840. This means that the CRI is between 80 and 89 and has a temperature of 4,000K. The first digit is the CRI and the second and third are the temperature. The Philips de Luxe Pro is 965 so CRI is 90 or higher with a temperature of 6,500K. Even with all this info it is not possible to really tell what the colour of a particular tube is going to be until you see it for yourself. Generally speaking the higher the CRI the better the light is at representing different colours.

Results

Osram Lumilux T5 840 Fluorescent Tube - This tube by itself looks quite white but when next to a daylight tube it has a definite orangey glow to it.
Osram Lumilux T5 865 Fluorescent Tube - A daylight tube but with a lowish CRI and is a bit too green for my liking. If you want a daylight tube on a budget then this is possibly OK.
Osram Lumilux T5 880 Skywhite Fluorescent Tube - Very bright white with a hint of blue/purple. Red's don't show up too well.
Philips de Luxe Pro T5 965 Fluorescent Tube - Very good daylight tube and could be used by itself if need be. Still a bit green for my liking but seems to give a nice range of colours in the tank.
Sylvania Grolux T5 - Very pink/purple looking tube. Looks a little dim compared to the other tubes due to it having not much in the way of green wavelengths.

These are the tubes I took photos of my tank with:
Osram Lumilux T5 840 Fluorescent Tube 54W
Osram Lumilux T5 880 Skywhite Fluorescent Tube 54W
Philips de Luxe Pro T5 965 Fluorescent Tube 54W
Sylvania Grolux T5 54W

Osram Lumilux 840

Osram Lumilux 880 Skywhite

Philips de Luxe Pro 965

Sylvania Grolux

Osram Lumilux 880 Skywhite + Osram Lumilux 840

Philips de Luxe Pro 965 + Sylvania Grolux

Osram Lumilux 880 Skywhite + Sylvania Grolux

Conclusions

Colour is a personal choice so I'm going to leave it to you to decide which tubes you think are best. The filter tube at the back top left of the tank in normal daylight is white in colour. From the various photos above you can quite easily see the different colours of the fluorescent tubes by looking at this tube. Also looking at the wood I'd say it looks quite similar in natural daylight to the last two photos. The Sylvania Grolux tube is the most expensive tube I tested but I feel it gives a rich mix of colours when blended with daylight tubes. If you like rich greens then the Philips de Luxe Pro 965 tubes by themselves are also very good. I would have used the Osram Lumilux Deluxe 965 tubes as these are supposed to be very good and are used in Europe, but unfortunately seem to be unavailable here in the UK UPDATE: I believe a version of these are now available - Check Lamp Specs for details. I would guess that they are very similar to the Philips de Luxe Pro 965 tubes I have used.
Just in case you are wondering, I'm using the Philips de Luxe Pro 965 and Sylvania Grolux combination.