lumens to par/pur conversion

[jaysonsd]

Hey everyone, was talking to a fellow reefer about a new mh bulb I was buying and that it listed lumen count (supposedly 3000 for the 14k I bought) and didn't list par. He said he read about a conversion on RC, but I, for the life of me, can't find it. Anyone familiar with it, if it exists? Or can ya tell me if 3000 lumens is a decent rating for a 70w mh?

Thanks,
Jayson

 

[shag26272]

I cant answer your question but which bulb do you have??

 

[jaysonsd]

Found it on reefshops.com. Its made by 'marine color'; came from China, couldn't pass up the fact that it was 20bux w/ shipping. If it puts out crappy light or the sps don't take, I'm only out 20 and can swap the old bulb in until I get something else (moving from a 20k unknown make to this 14k).

 

[shag26272]

the best bulb in the 70watt variety is the astralux 14k. btw, par is the portion of the light spectrum thats referred to as photosynthetically active radiation, lumens are a measurement base on what the human eye can see, im not sure if there is some type of conversion for this and if there is it is probably very complicated

 

[hahnmeister]

shag is right, there is no way to convert directly... they are measuring two different sets of wavelengths. Its just like saying, 'how much light 10% blue, 40% green, and 50% red equals the light of 33% blue, 33% green, 33% red?' You cant compare the two directly. That being said, if the wavelength of the bulbs do not change, you could come up with a rough conversion for things that dont change... but comparing different color bulbs will lead to errors if comparing PAR and lumens/lux.

As you can see from the following tables, the direct conversion is not possible, as it varies depending on the color of the bulb/source...
http://www.apogee-inst.com/conv_fc.htm