The apparent brightness of a planet is related to its size and distance from its parent star. You've stated your brown dwarf has a mass of ~45x that of Jupiter, but planets much heavier than Jupiter are likely to just be a lot more dense and not actually that much larger. Wikipedia has a handy list of known brown dwarf stars including size and mass estimates, and you'll see that those around 40Mjupiter migh be as small as 0.8 jupiter-radii, or perhaps larger than 2 jupiter-radii, but mostly these things seem to be about the same size as Jupiter, which is handy.
The other figure you need to know but haven't stated is the brown dwarf's geometric albedo. I won't go into detail here, but I'll use Jupiter's value of ~0.538 for now.
Now, given that the brown dwarf is probably the same sort of size as Jupiter, and I've declared it to be the same sort of colour and reflectiveness as Jupiter, you can use the real Jupiter as a proxy for all further calculations. I'll also be using the normal Sun as a proxy for your star to make things easy.
The formula for apparent magnitude (how bright things look to an observer) is
$$m = H + 5\log_{10}\left({d_{BS}d_{BO} \over d_0^2}\right) - 2.5\log_{10}\left(q(\alpha)\right)$$
where $H$ is the brown dwarf's absolute magnitude, $d_{BS}$ is the distance between the primary star and the brown dwarf, $d_{BO}$ is the distance between the observer. In this case, they're both conveniently 1.175 AU. $d_0$ is a unit conversion factor, which in this case will be 1 AU because that's the distance unit we're using. The phase angle $\alpha$ between the planet and the brown dwarf will be a constant 60° thanks to their trojan relationship.
Because planets are 3D rather than nice flat sheets, you need to use something called the phase integral $q(\alpha)$ to work out the proportion of light that gets reflected towards the observer. Modelling your brown dwarf as a diffuse reflecting sphere (which is reasonable), you get a constant phase integral of ~0.41.
You can compute a planet's absolute magnitude $H$ using the formula $H = 5\log_{10}\frac{1329}{D\sqrt{p}}$ where $D$ is the object's diameter, and $p$ is its geometric albedo. For Jupiter, this gets you an absolute magnitude of ~9.5.
Throwing all our numbers together, you end up with your brown dwarf having an apparent magnitude of -6.67. This is pretty bright... brighter than any planet in the solar system seen from Earth (~5 times brighter than Venus), bright enough to see during daylight. It might even case faintly visible shadows at night time if your eyes are sharp enough. The moon is still >300 times brighter though.
The apparent angular diameter of your brown dwarf as seen from your planet is ~2'48" of arc. This is approximately the apparent angular diameter of the Mare Vaporum of the moon, which is here:
(image source wikipedia, credit Gregory H. Revera)
You might be able to go an do a size comparison for yourself one night. This is large enough that your brown dwarf will be clearly visible as a blob, not a simple point of light, though do note that it won't appear to be circular because the phase angle means that only a portion of its surface will be brightly illuminated by its parent star. A good pair of binoculars should resolve large surface details if there are any (there may not be), and maybe even any large moons.
The "dark" side of your brown dwarf may or may not glow, depending on the age of the solar system and the amount of deuterium and helium-3 that it was formed with. Given its mass, it would probably be in Spectral class T, being heavy enough to burn deuterium but too light to burn lithium. A possible example of this sort of planet in real life might be Gliese 229B, a 40-60 jupiter-mass brown dwarf.
Alternatively, a younger world might be a lot more like Teide-1. It has a surface temperature over 2000K and a luminosity maybe as high as 0.0005 that of the Sun (but more on that in a moment). Unfortunately, Teide-1 is estimated to be 100 million years old or younger, and as such probably has a reasonable amount of its original supply of fusibles still remaining. 100 Myr isn't really very long by the standards of planetary evolution, let along the appearance of life (assuming the timescales of development of Earth are typical, of course). Gliese 229B may be as old as 3 billion years (according to Physical Properties of Gliese 229B Based on Newly Determined Carbon and Oxygen Abundances of Gliese 229A, arxiv) and as such is a better candidate for the appearance of your brown dwarf.
A more pessimistic take would end up with an old, cool brown dwarf with a surface temperature of <500K. This is also plausible, especially if your solar system is at least 4 billion years old, as ours is. Such a brown dwarf would not glow perceptibly.
(cropped from wikipedia, image credit MPIA/V. Joergens)
Finally (probably), luminosity. Teide-1 has a luminosity of 0.0005 that of the sun. Gliese 229B is much dimmer and cooler, and has a luminosity of 0.000011 times that of the sun. However, luminosity is the total amount of radiated energy, and as the Planck radiation formula tells us (in a complicated way you can gloss over for now) the actual spectrum of radiation emitted by a black body depends on its temperature. With a surface temperature of 2400K, Teide-1 only emits 4% of its energy in the visible spectrum. At only 950K, Gliese 229B emits less than 0.0001% of its energy as visible light.
Now, I'm less certain about turning these numbers into apparent magnitudes, so take these results with a bit of salt... my working suggests the brown dwarfs could be surprisingly bright which seem suspicious, but I don't have any better figures to go on right now. Teide-1 would be 50000 times dimmer than the sun, but that's still 8 times brighter than the full moon and quite bright enough to cast shadows at night. Gliese 229B by comparison would glow at magnitude -4.4... quite bright by the standards of our solar system, as bright as the brightest planets in our own sky, but isn't going to be casting shadows. The "dark" side would glow about 1/8th as bright as the sunlit side as seen from your trojan planet. The cool brown dwarf would not visibly glow.
All three dwarfs would produce a reasonable amount of near-IR light and be clearly visible in that spectrum. Teide-1 emit more than 30% of its energy output in the 650nm-1400nm band and would appear very bright, and even Gliese-229B emits 0.5% of its energy in that band. Longer wavelength IR is strongly absorbed by water and so would likely be less visible from the surface of your habitable trojan world. Night vision on your trojan world with one of the brighter dwarfs could be quite effective, though naturally evolving useful near-IR vision is likely to be challenging, because vision tends to rely on energetic short-wavelength photons with lazy long-wavelength IR photons getting literally lost in the noise.
