To put it exactly, the “rays” you described is actually wavefronts, but the wavelengths of visible light are too small for our brain to perceive as having wave-like behavior. However, the wave-like behavior of light can be observed through polarization and diffraction experiments.

Visible light is a kind of electromagnetic radiation in the form of energy emitted which exhibits wave-like behavior as it travels through space. Electromagnetic radiation does not have physical shape. Thus, our eyes cannot see light in physical manifestation. Instead, we see colors when light travels through space. However, phenomena such as the Photoelectric effect and the Compton effect offer ironclad evidence that when light and matter interact, the light behaves as if it were composed of particles having energy hf and momentum h/l.



The end result is that we must accept both models and admit that the true nature of light is not describable in terms of any single classical picture. In other words, the particle model and the wave model of light complement each other.

Assumption: All five filament bulbs are designed to operate on the fixed voltage (V). The brightness of the bulb depends on the power delivered to the filament (P = I²R), which depends mainly on the resistance of the filament. Therefore, our interest is the resistance of the filament that depends primarily on two factors: material it is made of, and its shape.

(1) Filament Material
Copper has higher electrical conductivity than Tungsten. Thus, Copper is a better conductor, and the current would pass through the filament without dissipating much energy, which means nothing would light up. Moreover, copper has lower young's modulus than tungsten, which means it will easily break.

(2) Filament Thickness
By R = ρl/A, a thick tungsten filament has lower resistance than an otherwise identical thin tungsten filament.

(3) Filament Length
Similarly, by R = ρl/A, a straight tungsten filament has lower resistance than an otherwise longer coiled tungsten filament.

(4) Inert Gas Pressure
The main cause of the failure of bulb is the evaporation of tungsten, which causes weak spots in the filament. By PV = nRT, the pressure is proportional to the temperature. As the temperature is raised, the filament evaporation rate rises. The inert gas also has the cooling effect.

Conclusion: To produce the brightest light among five, the characteristics of the bulb have to be (1) tungsten filament, (2) thin filament, (3) coiled filament, and (4) low pressure inert gas. And Bulb R has all these features.

I don't run the experiment to verity that but your point is valid. I made mistakes on Post #894 because I was misled by the marking scheme, and you probably should consider making a experimental validation. It is generally true that the brightness of a light bulb is a function of its filaments. For a given voltage of operation, a less resistive filament will draw more current, run hotter and will glow more brightly, as to say getting more incandescent.

Consider the following power rating of two bulbs:

(1) 120V 60W Bulb: The ideal filament resistance must be R = (120V)² / 60W = 240Ω. The measured rms current shall be approximately I = 60W / 120V = 0.5A.

(2) 120V 100W Bulb: The ideal filament resistance must be R = (120V)² / 100W = 144Ω. The measured rms current shall be approximately I = 100W / 120V = 0.8333A.

For more info, read this article [attachmentid=3464884], and study the experiment on the last page.