during vegetative stage, the type of light doesn't matter as much ... the typical 'vegging-lamp', with 'cool/blue' spectrum, produces less stem-stretch ... but, that depends on the wattage/lumens, too ... my 400 HPS vegged just fine, no significant stretch, at all ... but, during the more critical flowering phase, the 'warm/red' spectrum is much more recommended ... it mimicks the Autumn sun, setting lower on the horizon, etc. ... I grew a couple crops with HPS (red) from start to finish, worked out just fine ... I also owned a $90 'full-spectrum' growlamp, that wasn't visibly any better, than a generic $12 HPS bulb ... :smokin: