I am curious to know, what is the difference in light level from the surface of the typical aquarium to the substrate. I see some people with waterproof PAR meters have measured this but I wonder why there is so much attenuation. Is it typical to lose half the light from the surface to the substrate? Is it because light fixtures are poor at directing light downward or is it because plants are blocking the path of the light. I think it is better for the light just under the surface to be as close as possible to the light level at the substrate. In nature there should be very little difference between light at the just below the water surface and light levels at the 2' depth provided the water is clear and there are no obstructions. What do you guys think?
light attenuation
- Thread starter waj8
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In this forum it's not as much as what someone thinks (opinion) but what someone knows (or at least attempts to know by correlation and/or establishing significant differences). Please consider reading information already available here. Each tank is unique but as a rule of thumb standard tanks (say 21"H) one T5HO usually is all that is needed for most plants.
Pepetj
Santo Domingo
Pepetj
Santo Domingo
Thanks for the reply but that is not really what I am looking for. I want the know the ratio between the light just under the water surface and the light at the substrate. I finally built myself a good light fixture with high quality reflectors. It has made a huge difference to the light levels at the substrate with less wattage. From rough measurements I made with a camera I managed to at least double the light at the substrate without increasing light levels near the water surface. In other words, I reduced the surface/substrate light ratio. I like the tank much, much better this way. Since I don't have the right equipment to measure this myself I was wondering what other people are measuring who do have the right equipment.
waj8;60259 said:---In nature there should be very little difference between light at the just below the water surface and light levels at the 2' depth provided the water is clear and there are no obstructions. What do you guys think?
IIRC, there is a rule: the farther the light source from the substrate,
the less different light levels between a fixed distance.
The sun is very very far...
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On a cloudless days at noon, yes the light source is far away and there will be virtually no difference in light level from the surface to the substrate at 2' depth. On cloudy or windy days or in the morning and evening much less light would penetrate the water surface but I still imagine the light loss would be only slightly greater once the light got though the water surface as some of the light would have to travel a greater distance to the substrate.
I am more interested in how much attenuation you get with different light fixtures. I believe a fixture with parabolic reflectors and thin lamps will produce the best (for want of a better phrase) attenuation ratio. It's still not clear to me why there is so much light loss from the surface to the substrate though. A lot of light must be escaping through the sides of the tank before it touches the bottom.
I know it has been long known that good reflectors are helpful but I don't know just how much. I do know that when I switched from diffuse reflectors to parabolic specular reflectors the light at the bottom of my tank increased by a factor of at least 2 and possibly 3. I measured this with a DSLR camera so I couldn't get an accurate result but there was 2 stops difference. Same lamps but different fixture. I was rather shocked by this. I now see pearling on carpet plants with most of my lamps turned off. Anyway, I have long been interested in calculating light levels for a planted tank but without that ratio value it's impossible. Just wondering if there was any data out there now that some people have such nice meters.
I am more interested in how much attenuation you get with different light fixtures. I believe a fixture with parabolic reflectors and thin lamps will produce the best (for want of a better phrase) attenuation ratio. It's still not clear to me why there is so much light loss from the surface to the substrate though. A lot of light must be escaping through the sides of the tank before it touches the bottom.
I know it has been long known that good reflectors are helpful but I don't know just how much. I do know that when I switched from diffuse reflectors to parabolic specular reflectors the light at the bottom of my tank increased by a factor of at least 2 and possibly 3. I measured this with a DSLR camera so I couldn't get an accurate result but there was 2 stops difference. Same lamps but different fixture. I was rather shocked by this. I now see pearling on carpet plants with most of my lamps turned off. Anyway, I have long been interested in calculating light levels for a planted tank but without that ratio value it's impossible. Just wondering if there was any data out there now that some people have such nice meters.