As far as I've understood 4 different wavelengths in the color spectrum are important in photosynthesis, 2 types of red (~620nM, ~660nM) and two types of blue (~440, ~470 nM).
Those are the most important 4, but Infrared and ultraviolet are usefull as well.
The menu of colors required differs for each type of plant. Using just cheap normal red and blue leds (630nM and 470nM) will be enough for tomatoes for example, but other plants are lot more selective.
Leds emit a narrow bandwidth of light and you'll there for find growlights emitting up to 11-13 wavelengths on the market.
Since a lot of research is still going on, the effects of using a very large number of colors is also
questionable, It may... for example help to add Ultra-violet leds, but the lowest wavelength of an UV-led is about 390nM, while one of ~300 would be most effective. How much UV-leds contribute is therefor a question.
Led companies are also trying to cover every wavelength possible, but still have a hard time doing that. Using a lot of "non-standard" wavelengths is there for a lot more expensive. The 660 and 440 nM leds are already 2-3 times as expensive as common red and blue leds. Other wavelengths leds can cost much more. In case your spices aren't that selective, it could be throwing away money.
What you would need is knowing the specific light requirements of the plants you want to grow. That can be quite hard since growing using Leds is still a relative new technique. There is some... data available, mostly agricultural, but a lot is still uncharted.
I don't know which spices you want to grow, personally I grow weed. What I know from fellow growers is that growing using led lights is great to decrease the costs of electricity, but that it can be quite hard to grow using leds only. Besides leds a lot of them use other light sources as well. CFLs for example cost close to nothing and emit a much broader bandwidth. Using a few cfls as well will give the plants at least some of the missing wavelengths resulting in better crops.
What I know of led-growlights is that they often use a ratio of 5-6 watts red to every watt blue.
It may be an idea to divide the led-part in 40% 620nM, 40% 660nm, 10% 440nm and 10% 470nm. Using extra non led-light as well a ratio of 20-25% non-led light and 75-80% led-light might be an idea. Unfortunately it's hard to give good advice on led grow since so much still is unknown.
The suggestions I make are by the way more complicated since I should mention all light emitted in lumen instead of watts. Led development is going quite fast and there is a huge variety in output per watt, depending on which fabrication method is used. To get a good balance in light one should keep that in mind as well. Using old types red, new types blue or vice versa will make a lot of difference.
Last grow remark, besides needing different wavelengths of light, the needs of plants are different during the whole journey from seedling to crop. While growing a little more blue is better, while flowering more red.
Personally I grow in a 2x3 ft (50x75cm) closet, have used 200 watts CFL so far and am planning to do the opposite of a lot of fellow growers by keeping the CFLs and adding 40 watts of common 630nM red leds.
If you ask me using leds for growing probably will be a matter of experimenting a lot for the next decades.
When building your own "sun", keep in mind that plant-DNA has developed in millions and millions years.
Plants there for "expect" seasons to be as they should and react on the difference in hours of daylight they get. One can "fool" plants to a certain degree by starting to grow in "summer" and after growing going from "summer" to "autumn" quickly, but if they "think" it's a certain season since you've set the clock a soft-/hardware failure resulting in 24/7 daylight or non at all will have a lot of effect in the development of the plants.