How do I know when my lights are bright enough?

[ReefsandGeeks]

I just started coral this weekend with a dimmable 165W LED over a tall 40 gallon tank. I put the coral where I'd like their final placment to be, and have my light turne down to about 25% of full power for both blue and white. I'll increase light just a touch every few days untill I get to the final intensity.

How will I know when I've reached the amount of light I should use for my coral? I know coral can bleach out if the light is too bright, but getting to that point would be already subjecting the coral to light that is too bright. So how would I know when is enough?

Also, as far as the blue to white(full spectrum) goes, do I need to acclimate the coral to both colors at the same rate, or can blue be set wherever and only need to acclimate the white light?

 

[RVANANO]

You need to get or borrow a PAR meter. Our LFS has one they lend out. It's got an eye connected to a reader via cable. You place the eye in the tank at different locations and the reader will display what the PAR is for each area.

 

[phillrodrigo]

Some clubs have them also. I know our club has one that is always on rotation

 

[mpderksen]

I've heard that the spectrum of LEDs give odd results, and that algae tends to grow more in more blue lights. I can't find anything really definitive on it, though.
Below are the results of my PAR testing at 2 different levels.
The "full" test is at 100% blue, and 80% white. You can see that setting them at 80% yields values very close to the calculated values.
Even at the lower levels, I'm still seeing bleaching of some SPS, yet the Zoas on the bottom seem stretched.

 

[chill86]

You may have the par level at the recommended rating for specific corals but they still need to acclimate to the light. I have had a lot of trouble trying to fine tune the leds to get good growth so I went back to mh and used the blues on the leds for supplemental lighting. I have a 150g tall reef and the led's are 20" off of the water on blue 40% white% 35% and I am still burning up coral even after a few months of acclimation. Btw, when the zoanthids are growing stalks, that means that they are not getting enough flow.

 

[ReefsandGeeks]

Thanks for te replies. I'll try to get ahold of a PAR meter and find the final settings i'd like to have my lights set at and acclimate towards that. Interesting point about the zoas, I'll keep that in mind while I watch them grow. Where can i find recomeded PAR values for different coral? Getting a reading is only useful if I know what they should be. Currently have a green birdsnest, zoas, green toadstool, hammer, and green finger leather.