An incandescent light bulb like a household bulb has an efficiency of about 5%. This means that 95% of the energy is converted to heat.

The design of a light bulb can be played around with to improve light output, but the trade off is reduced lifespan.

Generally speaking, you increase the light efficiency by running the filament at a higher temperature where, although the heat output increases, the light output increases more. But the problem is that the filament burns out faster. That's why halogens are more efficient because the halogen gas reacts less with the hot tungsten in the filament than the residual gas in an ordinary light bulb, so the temperature can be pushed up with an acceptable lifespan. Xenon reacts even less, so these are more efficient again.

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Cheers, Neil