LED Optics Angle Question - The Planted Tank Forum
LinkBack Thread Tools Display Modes
post #1 of 3 (permalink) Old 02-12-2013, 01:13 PM Thread Starter
Planted Tank Obsessed
Join Date: Jan 2013
Location: Los Angeles, CA
Posts: 400
LED Optics Angle Question

I am looking into a DIY CREE LED fixture that is suspended ~3 feet over the substrate (tank is 30" x 18" x 18" high) and was looking at 20 degree optics to control the amount of light spill. I made a mockup in Solidworks and at the substrate, there is full coverage, but not that much overlap.

Using Hoppy's LED Par Calculator, I am getting 87 PAR, assuming a 5 x 2 XM-L array (6" spacing, 300 lumen per LED). My question is, are LED fixtures supposed to be designed such that each LED has large coverage over the entire tank? I'm ok with spotlighting as long as I'm not cheating the equation somehow and ending up with far less PAR than I was expecting.
Chronados is offline  
Sponsored Links
post #2 of 3 (permalink) Old 02-12-2013, 04:30 PM
Planted Tank Guru
Join Date: Dec 2005
Location: Sacramento, CA
Posts: 21,015
That equation was derived from data from LED lights with rows of LEDs, from 2 to 4 rows, all spaced from 2 to 3.5 inches apart. It is reasonably accurate with 40 or 60 degree optics, and with some tweaking, with no optics. But I haven't tried it with 20 degree optics.

You can design your light so that each LED lights up most of the tank, so many LEDs contribute light to every spot in the tank, or you can design it so each spot in the tank is lit by only a few LEDs. For the latter you obviously need to concentrate the light from each LED enough to get adequate PAR. There is no requirement to do it either way or a combination of the two ways - it is a choice you have to make. The more LEDs there are lighting each spot, the more you can mix in different colors without getting ugly colored shadows, and the more likely you are to have uniform lighting over most of the tank. But, this does mean the ends of the tank will be at a lower PAR than the middle, since there will be many fewer LEDs lighting the ends. If each spot is only lit by one LED it is possible to have virtually the same PAR along the entire length of the tank. But that is likely to show spotlighting effects too. It is a trade-off.

For an accurate PAR reading you have to use a PAR meter and measure it yourself. All that an equation can do is get you in the right ballpark, so a dimmable driver or drivers will let you adjust to the PAR you want.

Hoppy is offline  
post #3 of 3 (permalink) Old 02-14-2013, 06:47 PM Thread Starter
Planted Tank Obsessed
Join Date: Jan 2013
Location: Los Angeles, CA
Posts: 400
Thank you for the response, I think I've got a direction to head in now!
Chronados is offline  

Quick Reply

Register Now

In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome