Par

[Craig Matthews]

I've replaced my two t8 fluorescent tubes to two t8 LEDs . The LEDs say the par is 167 at 20cm. If the LEDs are around 50cm above the substrate level would the par drop off alot? There is two of them so they should be ok for a low tech?

 

[John q]

. If the LEDs are around 50cm above the substrate level would the par drop off alot?

Yes, the par will drop quite significantly.
Without getting to technical for you, and me, we can use a formula called the Inverse Square law to try and work it out. Basically if the distance doubles the light intensity can be divided by 4.

If we raised the light to 40cm it would equate to 167 ÷ 4 = 41.75 par.
In your case at 50cm the par output would be around 26.72.
This isn't exact science in an aquarium full of water, refraction, reflection and shading will throw these numbers off, but it will be near enough 😉

If you have two of these fixtures in a low tech tank you have ample light and may well have to raise the lights further or dim them a tad.

 

[Zeus.]

Plus what's the output of the original T8 ? T8 output vary from different types and is usual in lumens and there isn't an accurate conversion from Lumens to PAR or watts esp when comparing between light sources of different technologies.

PAR data is the only data which is really useful for our tanks and manufactures of light sources don't often supply PAR data IMO

 

[Craig Matthews]

Yeah don't get to technical I'm a simpleton haha. The t8s I took out 30 watts each they was fluval aqua glo 90cm I don't have the box anymore for any additional info and I can't find any fine details online. They are dimmable so I'll just have to give it a while and go from there. I was thinking about modifying the lid and having the t8s and LEDs but think that a recipe for an algae farm in a low tech. The LEDs are so much brighter than the old t8s for sure though.

 

[John q]

The t8s I took out 30 watts each they was fluval aqua glo 90cm I don't have the box anymore for any additional info and I can't find any fine details online.

Just to complete the circle. Each of those original T8 tubes provides 900 Lumens.

 

[Craig Matthews]

Just to complete the circle. Each of those original T8 tubes provides 900 Lumens.

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Wow your obviously better than me at this internet thing I couldn't find it anywhere I looked at about 10 websites. Tha you for that John. I put the LEDs in yesterday and boy the plants are literally up almost illuminated. I know pearling only happens with co2 but my valis I've had in there for about two months was absolutely benine didn't grow at all, no taller or any new leafs or runners just stayed the same. After an hour or so the LEDs were in the valis started bleeding and realising O2 bubbles which it never did with the old t8s and it's doing it again today in a different place with no visible wound to the leaf. My crypts have bubbles under the leafs and the sessiflora all point towards the light now like arrows and they close up at night now which they did neither with the other t8s. I think it's safe to say these LEDs are alot more potent that the t8s. I was sceptical because they are retro fit. It's the super fish retro bright 900mm was £37 each I'm pretty happy with that when you can buy a fluval aqua sky for triple the price and I don't think the fluval are much better other than colour changing I had it in the past and it didn't light up my old tank like these do.