The volt drop is different across each bulb. The 4.2W bulb uses the most power due to less resistance and will light up while the other two bulbs will use less power because smaller voltage but as you say the same current. The 4.2 W is the rating of the bulb (max power) so will probably light up to much and break.

You haven't stated the voltage, but let's go with 230 V.

The rating will be at 230 V.

W = VI so for the 4.2 W lamp, I = 18 mA. R = V/I = 230/0.018 = 12.6 kΩ.

For the 50 W lamp, I = 0.22 A and R = 1060 Ω.

For thé 60 W lamp, I = 0.26 A and R = 880 Ω.

Total resistance = 14.5 kΩ.

Current through the series = 16 mA. W = I²R. So the 4.2 W lamp draws 3.2 W, which is enough to illuminate it. The 50 W lamp uses only 0.27 W, so it gets a bit warm and does not glow. The 60 W lamp gets 0.23 W, which is even worse.

HTH.

Ah that makes sense I thought that was the processes but I wasn't sure if I was maybe miss understanding 

Just to add to to Chris P's answer - presuming we're talking simple filament (incandescent) lamps - that the "cold" resistance will usually be significantly lower than it's normal working resistance (when it's perhaps a couple of thousand degrees hotter) - so the 50W and 60W lamps probably get an even lower share of the voltage in practice than calculations based on normal working conditions would suggest.

   - Andy.

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 you get twenty multicoloured 12 volt bulbs with the same wattage and connect them in series to a 240 volt supply, you’ll have a set of Christmas tree lights.

And if you are bit mean and don't like buying replacement Christmas light bulbs, you can use pilot lamps or small vehicle bulbs wired in series, colour them by hand if desired. Back in the day, replacement lamps for Christmas lights were a shilling each, a significant sum then.

But if vehicle side light bulbs or pilot lamps could be obtained from ones work ?