Could somebody explain to me why in a series circuit with 3 lights one at 4.2w , 60w and 50w only the 4.2W lamp will light up I understand that the current will be the same through out but I am a little confused thank you

If in doubt try the practical experiment, obtain three mains voltage filament lamps of the stated wattages and connect them in series to the mains. Firstly observe that only the lower wattage lamp lights. Secondly measure the voltage across each lamp and observe that very nearly full mains voltage is present across the lowest wattage lamp and that only very low voltages are present across either of the higher wattage lamps. This only works with traditional filament lamps, various perplexing results may be obtained with low energy lamps.

Lamps of differing wattages CAN be used in series provided that they are of the same current ratting. For example a 20 volt 3 watt and a 230 volt 40 watt lamp  will burn in series on the mains as the current ratting is 0.15 amps or very close thereto in both cases. 

For reliable long term operation, the current ratings have to be closely matched. Trams used 5 lamps in series each of 110 or 120 volts nominal, on the trolley wire voltage of about 550 volts DC. These lamps were specially manufactured, or specially selected from standard production, for accuracy of current rating.

Early Southern region electric trains used 65 volt lamps, ten in series for interior lighting, from the conductor rail voltage which was then 650 volts. Later trains used a motor generator set to produce 65/70 volts from the live rail rail, this being safer than hundreds of volts to earth on lamps within reach. A 64 volt nominal battery supplied emergency lighting and also control circuits.

If in doubt try the practical experiment, obtain three mains voltage filament lamps of the stated wattages and connect them in series to the mains. Firstly observe that only the lower wattage lamp lights. Secondly measure the voltage across each lamp and observe that very nearly full mains voltage is present across the lowest wattage lamp and that only very low voltages are present across either of the higher wattage lamps. This only works with traditional filament lamps, various perplexing results may be obtained with low energy lamps.

Lamps of differing wattages CAN be used in series provided that they are of the same current ratting. For example a 20 volt 3 watt and a 230 volt 40 watt lamp  will burn in series on the mains as the current ratting is 0.15 amps or very close thereto in both cases. 

For reliable long term operation, the current ratings have to be closely matched. Trams used 5 lamps in series each of 110 or 120 volts nominal, on the trolley wire voltage of about 550 volts DC. These lamps were specially manufactured, or specially selected from standard production, for accuracy of current rating.

Early Southern region electric trains used 65 volt lamps, ten in series for interior lighting, from the conductor rail voltage which was then 650 volts. Later trains used a motor generator set to produce 65/70 volts from the live rail rail, this being safer than hundreds of volts to earth on lamps within reach. A 64 volt nominal battery supplied emergency lighting and also control circuits.