This is a review of the 20-27" model (so I guess the medium sized one). Also note this is an initial impression review. As I just received this item and installed it on my tank, I do not yet have any long term experience with it. And also, I run my tank lights off timers, so I have set the light to fully on and let the timer turn it off/on each day and so don't use the "blue LEDs only" option. But this light does work fine off a standard light timer (one of those mechanically operated ones with the round face the slowly rotates and you put the little plastic pieces in at the times you want on or off)LED Aquarium Hood Lighting Fish Tank Light for Freshwater and Saltwater, Blue and White LightMy standard 10 gallon tank's hood finally crapped out on me. It was your standard 15W, 18" T-8 fluorescent light hood which served me well for over 20 years. But now was an opportunity to upgrade. I do grow easy low light plants in my tanks so I wanted to upgrade to LEDs but also needed to make sure the light was at least equal in brightness to a standard 15W T-8, which is roughly 800 lumens. This light is noticeably brighter with a very natural sunlight look (I was worried it would be too blue looking but it isn't). I tend to buy 5000K lamps and find ones upwards of 6500L+ to be much too blue for my liking. This hood appears very much in the 5000K to 6000K region I prefer so very happy there.A standard 10 gallon is about 20 inches long, so one might think the smaller version, the 11-19" model is just right. And if you don't group any live plants that model is probably going to be perfect for most people. But if you have any ideas of growing any sort of live plants, then I would strongly suggest the 20-27" model is the way to go. It fits a standard 10-gallon tank perfectly, stretching across the entire length and still a enough room on each side for the legs to sit on the tank edges.This particular tanks is neither heated (I keep common guppies in it which do well in cool tanks) nor does it house any fish known to be jumpers. So with this new light I opted to remove the entire hood and am running the light over open water (I have a 30 gallon I have run this way for years without issue). However if you have a full hood with the removable light strip on it (fairly standard), you can use this light with the hood. You just position it over the glass strip where the old strip light used to sit. It does sit a few inches over the glass so I think too much light is lost to the room rather than directed down, but it will work fine if you need to keep heat or jumpers in the tank.Attached photos are to show 1) how well the light fits over a standard 10-gallon (using no glass or hood), 2) How nice the light looks in my planted tank (yes the java moss needs to be thinned out a LOT) 3) how the feet of this light sit on the plastic trim piece of a standard glass aquarium, and 4) how high above the water/hood/glass the light will sit.One thing to keep in mind is that if you use this over a glass top, a lot of light is likely to be reflected up into the room making for a brighter room that just what a lit tank would normally add.