Perceived Brightness: Are my eyes fooling me?

[-Logzor]

The other afternoon I picked up some frags from a local reefer. He runs 2x400w MH on his 90g system. Gets insanely growth rate, great color, etc.

One thing I noticed is that my aquarium looks way brighter to the naked eye. I'm only running 7x54w T5's on my 150g.

I noticed that his Appleberry Montipora was in almost complete shade, under a large tabling acropora. It had perfect color, deep green, blue polyps. Mine tends to be super-washed out, even though it's at the bottom of the tank.

So what gives? Is my tank actually more bright and putting down more light or are my eyes fooling me?

I raised my light fixture way up, we'll see what happens.

 

[Poseidon]

Our eyes are TERRIBLE at comparing light from one tank to another, especially when they are not right next to each other.

Short answer to can T5 be "brighter" then halide? Absolutely.

Long answer... Get a PAR meter and measure it.

 

[mgdmirage]

T5s can really fool your eye though because of their even coverage instead of point source.

 

[caudill187]

T5s can really fool your eye though because of their even coverage instead of point source.

Agreed here. "brightness" is produced by more light leaving a tank in a horizontal direction, thus more light to stimulate our retinas. This does not necessary translate to more light, or more PAR available to corals. Halide direct more of the light in the vertical, downward direction toward the corals...so do LED's.

 

[-Logzor]

Agreed here. "brightness" is produced by more light leaving a tank in a horizontal direction, thus more light to stimulate our retinas. This does not necessary translate to more light, or more PAR available to corals. Halide direct more of the light in the vertical, downward direction toward the corals...so do LED's.

That's a really good point. I suppose this also means that T5's are hitting the sides of the corals A LOT more than MH bulbs.

 

[shred5]

Well cetain color light will look brighter to the human eye. I work in the lighting industry and we have tricks to lower light levels and make it apear brighter.

Funny thing is in a reef tank usually halides apear brighter.. T-5 usually have more efficent reflectors that direct the light straight down so there is less wasted light. Halides usually bounce light around more so they hit your eyes and also reflect off walls etc. thus appearing like there is more lights. Could be his halides are also higher kelvin which makes them appear dimmer too. You may actually have more light.

Par numbers are not right when measuring t-5 and especially leds. They are narrow spectrum where halides are more wide spectrum. Par meters will read certain wavelengths of par higher than they are and other wavelengths lower than they are. Basically a par meter will read halides more accurately than t-5 or leds. It one reason people are getting bleaching events so easy with them. They have higher par than whats read.

Apogee Instruments Quantum Sensor - Spectral Response

 

[-Logzor]

That's some really great information, thanks for posting. I've always suspected that T5's were a lot more powerful than people realize, even if using a PAR meter, matching their MH counterparts. Notice that most T5 tanks have corals that are much lighter in appearance, as well as "pastel" coloration. I think this is 100% due to having too much light.

 

[pumarjr]

LEDs are notorious for having an unassuming appearance. You may think with LEDs as with T5's that your tank is not that bright, but slap a par meter on there and see how the par numbers are doing.