jm23
Active member
This thread comes from a thread Maidia posted on R2R while CR was down the other day. Mai brought up a good question about whether optics are really needed on an LED fixture and I wanted to post it here for those looking into buying an DIY LED fixture and were wondering about which optic or no optic.
LEDs have a built in optic of about 120°. This means that if you draw a line straight down from the center of the LED it will spread 60° off center every direction. So lets look at some numbers.
120° optics (60° coming off of center) equals 41.56" spread on the sandbed at 24" above sand and a 51.96" spread at 30" above sand. So one LED without optics will spread over 83" on the sandbed at 24" above the sand.
80° optics equals 20.14" spread at 24" above the sand and 25.17" spread at 30" above the sand. So one LED with 80° optics covers 40.28" at 24" above the sand.
60° optics equals 13.85" spread at 24" above the sand and 17.32" spread at 30" above the sand. So one LED with 60° optics covers 27.7" at 24" above the sand.
My recommendation would be to use optics. Most people have a 24" high tank and mount the LEDs between 6" - 10" above the water line. So most people are somewhere between 30" - 34" above the sand with their LEDs. Using optics allows for a more efficient use of your LEDs, preventing spillage outside of the tank. I will note that if you have a preexisting non-dimmable fixture and are getting too much light for your corals you can either raise the LEDs higher (not possible for people with canopies) or remove the optics.
Some other things to consider:
LEDs have a built in optic of about 120°. This means that if you draw a line straight down from the center of the LED it will spread 60° off center every direction. So lets look at some numbers.
120° optics (60° coming off of center) equals 41.56" spread on the sandbed at 24" above sand and a 51.96" spread at 30" above sand. So one LED without optics will spread over 83" on the sandbed at 24" above the sand.
80° optics equals 20.14" spread at 24" above the sand and 25.17" spread at 30" above the sand. So one LED with 80° optics covers 40.28" at 24" above the sand.
60° optics equals 13.85" spread at 24" above the sand and 17.32" spread at 30" above the sand. So one LED with 60° optics covers 27.7" at 24" above the sand.
My recommendation would be to use optics. Most people have a 24" high tank and mount the LEDs between 6" - 10" above the water line. So most people are somewhere between 30" - 34" above the sand with their LEDs. Using optics allows for a more efficient use of your LEDs, preventing spillage outside of the tank. I will note that if you have a preexisting non-dimmable fixture and are getting too much light for your corals you can either raise the LEDs higher (not possible for people with canopies) or remove the optics.
Some other things to consider:
The par will drop for every inch off center you go on the sandbed.
- If you only have, say one red LED per unit, you might want to consider leaving it without an optic in order to avoid banding (a red spotlight on the bottom of your tank)
- Use dimmable drivers in combination with your optics in order to prevent bleaching / photoshock and ramp the unit up over time.
