what to replace candles

You can always use stones. That's what I use a lot. You can used stones that are a color that represents each element.

Or use an object that represents each element. Like a feather for air, bowl of water for water, ect.

salt for earth? But what about when casting a circle? I was following something that involves a bigger white candle in the center of the circle for invocation of a goddess.

There are many different types and ways of casting a circle actually. Casting a circle just helps keep your energy contained and outsider energies away to help you focus.
Those that have practiced a lot and have great concentration don't even need a circle. That might be where you heard of the white candle. I have heard of people doing that to and have done it myself.
Again though, its concentration. A circle is recommended to help out those that are new to help them focus and keep them safe aswell. You could try without a circle but if your a newbie, you will probably find it very hard to summon up a lot of concentration and hard to block outside energies as well. I wouldn't try anything without a circle until your used to concentrating your energy and blocking outside ones.

One can also add that when casting a circle you don't need candles. You can simply call the elements come to your circle and bless your space (though I would recommend having a representative (rock or salt for earth, bowl of water for water, a feather or even an open window on a breezy day for air, and charred wood or maybe charcoal to represent fire (though you might be able to use a statue of a dragon)) Many keep in their mind that it is a sphere or a cone for gathering energy until you are ready to release it. Now another reason to use a circle, especially as you start out is that this sacred space is generally a place between here and the ethereal. This makes it a prime place to gather you energy and send it out. Also if you aren't gonna use a circle I suggest in some way getting the negative energy out of your room or space.

Thank you so much for all the help.
I have read that same thing somewhere also that you can cast a circle without candles --- except for invoking the deities wherein you have to have a candle in the center. Is it any true? Or can you replace the candle with anything else?

If you have a little statuette to represent the deity(ies) you'll be just fine. Do not use the same statuette for multiple divinities.

incense is the one thing u can replace candle ,like what chinese doing thing

HI everyone...
The problem is...I am on sa boat and candles are not allowed for safety reasons.
What can I do in place of candles?

Since you are on a boat, i agree with Stones or Crystals. Blue calcite for water/West... etc... as for replacing the white candle, i would use a clear quartz crystal or a goddess statue or some symbol. Casting a circle should be fine without the candles.

Thank you for the help SunshineVal...