A 625W dimmer is quite a big unit. Remember with GU10 lamps you need to add extra 25% to rating. I know you can get 1000W dimmer units but the problem is they often also have a minimum rating too. So typical 200W to 1000W which means one has to be careful to replace any blown bulbs.
Of course one should not really dim quartz halogen lamps. To work they need to be at the correct temperature. The idea is the quartz is so hot the tungsten can't re-deposit itself on the quartz so it is re-deposited on the tungsten filament.
So normally one would not use a dimmer with quartz lamps but use a 1/3 and 2/3 split so 4 on one switch and 6 on another so you can have 4, 6 or 10 lamps on.
Hi thanks for the reply Eric ,my dimmer switch was a 400w max , I have ordered 10 new bulbs at 35w so new total 350w but I may see if I can get a dimmer with a higher rating. Do you think a dimmer is a bad idea with the Gu10 bulbs ? Maybe I should just change the dimmer for a standard switch ?
I would not normally use a dimmer for quartz lamps. There are of course exceptions where for some reason one has to except the shortened lamp life but in the main a standard switch is better.
Although you can get powerful dimming switches they tend to be very expensive and of course lamps do blow so the dimmer really needs to work from a single bulb to all bulbs and as far as I can see all the very powerful dimming switches will be damaged if under loaded and well as overloaded.
There is also a problem with heat. 500W is a fair amount of heat and the room would need thermostatic radiator valves or the like to compensate for the heat from bulbs. If the main thermostat was in that room switching on lights would mean rest of house would get cold.
Reducing the lamp sizes will help with heat problem.
Personally I find the 50mm spot lights are great for when a spot is required. For example as a bedside lamp shinning directly on my book, lighting a picture on the wall, or an area well away from the light source where normal lights would not reach. However for general lighting they are rubbish.
People refer to them as mood lighting but really you only what that as an extra for when the mood suits not as only lighting. By moving to a plain switch it opens up the options to use other types of lighting. It does not really matter if you fit cold cathode lamps into existing GU10 holders or if you swap fitting and replace at least some lamps with for example 2D light fittings until the dimmer is got rid of you can't use them.
I replaced all my fittings in living room and dinning room with CFU's which take some time to reach full brightness so even without a dimmer we still get a soft start. So they do not wake my wife if she falls asleep in chair when I switch on the lights.
Most houses some where have ceiling roses which are used as junction boxes and rated at 5/6A so the consumer unit will likely have a 5A fuse or 6A MCB so with one room using 2A there is a good chance from time to time the 5/6A is exceeded plunging you into darkness so I would be looking at a method to reduce the power going to your lamps.
There are a few lamps which are LED and discharge that can be dimmed but in the main most need a standard on/off switch.
I have an 11W cold cathode GU10 lamp on the wall behind the bed to read with one side and a 50W quartz halogen the other side. Although the 11W lamp is good enough at 3 foot to light the page the 50W is far better and I have never been temped to change the second lamp to cold cathode type.
With 10 lamps in a room likely the 11W lamps would work OK but to fit 10 x 4W I think you will find is going too far. The spread of light is also important and cold cathode tends to have a bigger spread than tungsten but LED a smaller spread. So with LED lamps likely will look like a planetarium.