No you cant but you need to go in a area that's dark like a dim cave.
Pokemon LeafGreen does not have a time system. This makes it impossible to do evolutions that involve time such as evolving Eevee into Espeon or Umbreon.
I believe that you have to get the eevee to max happiness ( or really high ) and level it up in the nighttime.
In ANY GAME!! If you use a moonstone, i think
Trade it to ruby,sapphire or emerald have them evolve your evee at night then give it back to leafgreen.
so far, you cannot evolve eevee either to umbreon or espeon on FireRed because on FireRed and LeafGreen, there is no clock system. You must trade eevee to Emerald for evolving to Espeon or Umbreon
you can't. to get an espeon or umbreon, you need to evolve an eevee at certain time of day. leafgreen/firered don't have clocks. you have to trade the eevee to ruby/sapphire, max out friendship and level up in the pm for espeon, am for umbreon.
Eevee evolves into Umbreon (the pokemon you want) or Espeon when it is evolved in day or nighttime. Unfortunately, since Pokemon Leafgreen lacks an internal clock, you must trade your Eevee to Emerald/Sapphire/Ruby or later and let it evolve at night in order to obtain Umbreon. The daytime refers to the hours of 12:00 AM to 12:00 PM, and the nighttime refers to 12:00 PM to 12:00 AM. Have fun.
Umbreon
To make Eevee evolve into an Umbreon, you have to level it up with high happiness at night.
Eevee evolves to Umbreon when it has high happiness, and it levels up while it is dark.
you can get a shiny Eevee on Pokemon leafgreen but its rare. its about a 1/5000 to get it
You can get an umbreon by getting an eevee from bill in goldenrod city (in a house) and then you can evolve eevee into umbreon by making it happy and leveling it up at night time.