Hi,

I've been looking into some daylight kits and I saw one that carried 4 30w fluorescent ligth bulbs. I have read somewhere that a 30w fluorescent light is equivalent to about 150w regular. Is this right? Because in this case a set of 4 30w fluo light bulbs (total of 120w) would be equivalent to 600w, which is actually good.

It is my understanding that fluorescent light is 4 times as efficient as tungsten. That is, multiply the wattage of the flo by 4 and you get the comparative tungsten output. So, each one of your 30W flo bulbs will be putting out the equivalent of 120W tungsten. All four would be equivalent to 480W.

I'm not an expert in photometrics, so it would be best if someone (Richard of Cool Lights?) could verify my response.

~~Dave

Richard has pointed out that compact fluorescents are not as efficient as externally ballasted fluorescents. You might want to use 3x for compact fluorescents instead of 4x the efficiency of tungsten. The real benefit comes if you are trying to match daylight. The huge loss of using a full CTB blue filter in front of tungsten really makes fluorescent a better choice. That 120W of daylight fluorescent will be stronger than 650W of tungsten in daylight. If you really want to have strong daylight fixtures, look into the ones that have separate ballast and PL55 (55Watt) tubes. They are bright and reasonably compact.

Yes to be conservative, I would say 3 times then your expectations are set such that you won't be disappointed if the CFLs you choose don't seem as bright as you'd hoped.

Thanks, guys. This information helps a lot.

Better still, just take note of the number of rating in lumens.

Be careful with household fluorescents. I recently bought a 25Watt fluorescent bulb that said "daylight". It is relatively bright, but the cri of this lamp is more than bad. The light is very blue (at least 7000K I guess) but it lacks a lot of wavelengths. It looks very blueish and it is bright, but you don't see very well with it. It's a light I wouldn't want anywhere in my home...
You can use it as a daylight fill, but as your only light source it's worthless.