# Can someone explain PAR and how it relates to 10 w LED spotlight



## Zapins (Jul 28, 2004)

I'm bidding on a 10 w LED that puts out about 650 lumens of light. I am going to be using this light for my new experimental emersed setup.

The bulb is rated between 30 and 38 PAR, but I'm not sure if this is enough to grow HC from roughly 15 inches above the plants.

Can someone clue me in to PAR readings and if it will be enough light?

Also about how hot would this LED run?

Details of the bulb:
http://www.greendealsdaily.com/blog...eyond-cfls-but-are-they-ready-for-prime-time/
http://www.eternaleds.com/ProductDetails.asp?ProductCode=HP-10


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## doubleott05 (Jul 20, 2005)

Zapins said:


> I'm bidding on a 10 w LED that puts out about 650 lumens of light. I am going to be using this light for my new experimental emersed setup.
> 
> The bulb is rated between 30 and 38 PAR, but I'm not sure if this is enough to grow HC from roughly 15 inches above the plants.
> 
> ...


i wouldnt worry about par and all that 
you should worry about watts per gallon(i know its emersed) and the color kelvin value of the bulb preferably between 6500-8000kelvin degrees

leds dont run very hot from wht i have experienced and 12-15 inches should be enough 
i personally would put at least 25 watts over it

hope that helps

http://lightbulbs.com/led_light_bulbs.htm
the last paragraph in the article has a number people ther can help


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## cassiusclay (Feb 19, 2007)

i would have to say no on that one 30-38 PAR is not alot of light for plants to use. have you read this thread http://www.aquaticplantcentral.com/...light-intensity-variations-some-thoughts.html
some good info in there long read but you will understand more after it.


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## tropism (Jul 21, 2006)

When I first read this I thought the "between 30 and 38 PAR" was referring to Photosynthetically Active Radiation. I wasn't getting anywhere looking up info on that and what are considered 'good' PAR values.

Then I looked at the second link you posted (eternaleds) and noticed this sentence "_The HP-10 is a great replacement for canned, recessed or track lighting fixtures that use PAR30 or PAR38 floodights._" and it occurred to me that they weren't talking about Photosynthetically Active Radiation. Did another search and found this: "_PAR stands for either "Pressed glass Aluminized Reflector" or "Parabolic Aluminized Reflector," depending on who you ask. The 38 means it's 38 eighths of an inch, or 4 3/4", in diameter._" (from http://ths.gardenweb.com/forums/load/lighting/msg0111043013503.html)

So "PAR" can actually mean two different things related to lighting. (as if one PAR wasn't confusing enough) 

--

I can't say for sure if that's enough light, but I can tell you that I'm currently growing HC in a 40 gallon NPT. I have two 42-watt Coralife (normal output) T5 fixtures on the tank, but since the tank is 18" front to back and I have a lot of plants in there, 90% of the light from one fixture does not reach the HC. So basically it's growing for me with no ferts (until a couple weeks ago, as a test), no CO2, and maybe 1.2 WPG.

In purely practical terms, you could probably just use a screw-in CFL. They're not THAT much less efficient than LED*, but the LED light should last a lot longer. BTW, are you sure the bulb you're bidding on is the same as the one in the second link? That says 400 lumens...

*I found at least one CFL that's supposedly _more_ efficient -- 820 lumens using 12 watts = 68.3 lumens/watt, vs 650 (or 400 according to the eternaleds site) lumens using 10 watts = 65 (or 40) lumens/watt


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