What is Brightness: Definition and 144 Discussions

Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. It is not necessarily proportional to luminance. This is a subjective attribute/property of an object being observed and one of the color appearance parameters of color appearance models. Brightness refers to an absolute term and should not be confused with lightness.The adjective bright derives from an Old English beorht with the same meaning via metathesis giving Middle English briht. The word is from a Common Germanic *berhtaz, ultimately from a PIE root with a closely related meaning, *bhereg- "white, bright".
"Brightness" was formerly used as a synonym for the photometric term luminance and (incorrectly) for the radiometric term radiance. As defined by the US Federal Glossary of Telecommunication Terms (FS-1037C), "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light.A given target luminance can elicit different perceptions of brightness in different contexts; see, for example, White's illusion.
In an RGB color space, brightness can be thought of as the arithmetic mean μ of the red, green, and blue color coordinates (although some of the three components make the light seem brighter than others, which, again, may be compensated by some display systems automatically):




{\displaystyle \mu ={R+G+B \over 3}}
Brightness is also a color coordinate in HSL color space : hue, saturation, and lightness, meaning here brightness.
With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude.
Brightness is, at least in some respects, the antonym of darkness.

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  1. S

    Brightness of two lamps in a circuit having a changing magnetic field

    The answer key is (D) but I don't understand how to approach this question. I am guessing the wire is acting as short circuit path but how to know which bulb will be short - circuited? Thanks
  2. milkism

    Oscillating dipoles, energy and brightness

    Problem: Attempt at solution: So "energy passing through per unit area per unit time" is equal to $$I = \frac{E_i}{A t}$$ So for a the graph will be in the form of ##y=1/x##? For b) do we have to solve the differential equation $$dI = \frac{E_i}{A dt}$$?
  3. L

    B How bright is the Sun compared to the sky?

    What is the brightness of the sun compared to the sky that it lights up? I have a solar filter that only sees the sun. I just wonder if it is needed to be so dark that I can't see the sky anymore. I have plenty of camera options left to shorten exposure even with a filter a fraction as dense...
  4. Slimy0233

    I Heating a tungsten filament to find out the maximum brightness emitted

    I was taking notes from a lecture on Quantum Physics and during the introduction, they gave an example of what led to the discovery of Quantum Physics: The electric bulb example where the brightness and colour of light depended on the temperature of the filament(see...
  5. D

    B Exploring Light with a DIY Spectroscope

    Hello, I built myself a spectroscope with a CD (where I removed the coating), similar to this one: With this I now want to look at light sources. However, some interesting lamps are a bit too bright to comfortably look directly into (through the spectroscope). Does anyone have an idea how to...
  6. alan123hk

    B Measuring Light's Brightness & Power Flux Relative to Observer's Speed

    Assuming that the observer moves along the direction of the light, does the speed of the observer's measuring instrument relative to the light source (which may be close to the speed of light) affect the brightness and/or power flux density measured by the observer? I'm not sure about this...
  7. V

    B Newton's Rings central spot brightness

    How come when the illumination is from below, the central spot is bright, but when the illumination is from above, the central spot is dark?
  8. K

    I Do stars in the ecliptic seasonally change brightness?

    Has any astronomer observed any seasonal changes in the brightness of stars lying close to the ecliptic plane? (Other stars are: d Cnc b=+0.08, mag.=+3.9; d Gem b=-0.18, mag.=+3.5; a Lib b=+0.33, mag.=+2.7.) Once a year these stars are occulted by the Sun. What happens from the date of...
  9. M

    I Brightness and solid angle

    I have a doubt regarding the role of the solid angle when calculating the power(W) with the brightness of the source I'm observing with area Asource. I was given the definition: with A the Aantenna. If now I take as an example the picture below to calculate W, we conisder as solid angle the one...
  10. LCSphysicist

    Cavity and coals: brightness and its consequences

    Cavities formed by red-hot coals appear brighter than the coals themselves. Is the temperature in such cavities appreciably higher than the surface temperature of an exposed glowing coal? At first i tried to interpret the "brightness" as a synonymum of intensity, anyway, a radiation emitted by...
  11. K

    I Does a particular star's brightness change throughout the year?

    Since the Earth orbits around the sun and very slightly changes its relative angle and position, does the brightness of a particular star change from season to the season?
  12. J

    Understanding the effect of duty cycle on the brightness of LEDs

    The brightness of an LED is a result of the current passing through it. The current is a function of the voltage across the LED. The duty cycle represents the percentage of the time period that the signal is in the ON state ( which means that the voltage is at max value as compared to 0 V for...
  13. M

    Differences in the Brightness of bulbs for 2 separate circuits

    I came across 2 similar example problems while studying for my exam and I want to make sure I get the differences between the two before I take my test later this evening. (This might be long but I have an exam coming up and I don't want to go into it with any uncertainties. I appreciate anyone...
  14. K

    I Exploring Photo-Sensor Measurements for Brightness Change Evaluation

    Hello, I'm using photo-sensors from commercial and industrial cameras to document an experiment. Afterwarde I evaluate the change in brightness during the test of a fixed segment of every image I took. The ambient light condition is stable and the images are in raw files, but I'm unsure how raw...
  15. O

    Comparing the brightness of each bulb in a circuit

    Homework Statement Four identical light bulbs are connected to a battery as shown in the diagram. Switch S is originally closed. If switch S is opened, what happens to the brightness of each bulb? Homework Equations V=IR The Attempt at a Solution - By opening the switch, no more current...
  16. Krushnaraj Pandya

    Brightness change with temperature

    Homework Statement A black and yellow body at room temperature are thrown into a furnace at very high temperature. How will the initial and final brightness of both compare? Homework Equations λT=constant The Attempt at a Solution The rise in the black body's temperature will be higher...
  17. J

    Arrange bulbs in descending order of brightness

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] Sorry for the messy image . I have got the right answer by assuming certain values of the resistors . But I would like to know whether this question can be done logically without assigning numerical values to the resistors...
  18. B

    I Center of Image - Brightness Distribution

    Hello, I am reading a review on weak gravitational lensing (https://arxiv.org/pdf/astro-ph/0509252.pdf) and they define the center of an image as follows: $$\vec \theta_c = \frac{\int d^2 \theta I(\vec \theta) q_I [I(\vec \theta)] \vec \theta}{\int d^2 \theta I(\theta) q_I[I(\vec \theta)]}$$...
  19. M

    Brightness of bulbs depending on their watt level

    Homework Statement Two 110-V light bulbs, one "25W" and the other "100W" are connected in series to a 110 V source. Then: a. the current in the 100W bulb is greater than in the 25W bulb b. the 25W bulb will be brighter c. the current in the 100W bulb is greater than that in the 25W bulb d. the...
  20. B

    Current, voltage : brightness of bulb in parallel or series

    Hello I'm working through a book (with answers) but am struggling with voltage, current, resistance and circuits. Please check my understanding below and let me know if I've finally understood. Thank you. In particular I'm confused in Q2 Q1. A student connects light bulbs, A and B, and...
  21. G

    B What is the Relationship Between Candelas, Watts, and Brightness?

    The SMPTE 196M standard specifies screen brightness for cinemas, as 55 candela per square meter, open gate (no film in the projector, just white light). It used to be specified in terms of foot-lamberts, but let's stick to SI. I ultimately want to compare the brightness I see in a cinema, with...
  22. G

    How does changing projector lenses affect brightness?

    I have some questions about projection lenses and screen brightness. Background I may be purchasing a BenQ PU9730 (http://www.benq.com.au/product/projector/pu9730/specifications/) for use in a large venue, projecting an image 3 x 5.3 metres. The projection booth is 18m from the screen (maximum...
  23. J

    Brightness temperature in remote sensing

    Hi all, I don't know if I'm on the right forum to ask this, but maybe somebody knows anything about brightness temperatures measured by remote sensing devices. In a paper that I read "Atmospheric corrections for retrieving ground brightness temperature at commonly-used passive microwave...
  24. Asmaa Mohammad

    The rheostat and the brightness of the bulbs

    Homework Statement In the circuit shown in the figure, what will happen to the brightness of bulb A and bulb B when the wiper moves from point X to point Y? Homework EquationsThe Attempt at a Solution [/B] When the wiper moves towards Y we get smaller resistance, hence the current intensity...
  25. Asamad

    Sun ray brightness quality after mirror reflection

    What is the Sun ray brightness quality after mirror reflection and what affects it? How to get the efficiency after reflection?
  26. ikihi

    Ranking brightness of lightbulbs in a circuit

    Homework Statement In the circuit shown, all the light bulbs are the same. Why is the following statement true? : A is the brightest. B and C are equally bright, but are dimmer than A. https://pbs.twimg.com/media/C6GllsQVMAA4chz.jpg:large...
  27. I

    How does the luminosity equation work?

    I've read that L = 4 x Pi x b x d2 Where L = Luminosity (W) d = distance (m) b = brightness (W m-2) But in a real life applied situation, how does it work, how does one measure the distance and its brightness? And what does the 4Pi do?
  28. Biker

    Transformer and the brightness of bulbs

    Homework Statement The brightness of the bulb A in the following picture equals: A) half of the bulb B brightness B) equal to bulb B brightness C) Twice as bright as bulb B D) four times as bright as bulb B Homework Equations Ohms law Conservation of energy Faraday's law The Attempt at a...
  29. dykuma

    Surface Brightness at any angle

    Homework Statement Here is a picture of the problem https://www.dropbox.com/s/2bps6ga2o4hjpgw/hw4.png?dl=0 For those who don't want to click the link, basically the problem wants me to calculate the surface brightness of a flat surface at any angle if the source function S = B(T), which is a...
  30. RoboNerd

    Question on lightbulb brightness in circuit analysis

    Homework Statement Homework Equations I know that power of a lightbulb/resister is I^2 * R The Attempt at a Solution OK. Here's my attempt: Let's consider the situation where we do not close the lightbulb and assume that the wires and switch are ideal because they have no resistance. I...
  31. RoboNerd

    Lightbulbs and a battery circuit

    Homework Statement Homework Equations no equations The Attempt at a Solution I know that we will have an equal current flowing through bulbs 1 and 2 when we connect them in parallel in accordance with kirchhoffs voltage law which says that the voltage drops around both paths must be equal...
  32. C

    Brightness of Light Bulbs in a Circuit

    Homework Statement [/B] Given the circuit diagram (attached below), predict how unscrewing each bulb separately affects the brightness of the other two bulbs? Homework Equations N/A The Attempt at a Solution I predict that by unscrewing one of the bulbs, the other two will get brighter. This...
  33. kamhogo

    Identical bulbs, rank by brightness

    Homework Statement Which bulb(s) will have the higher light intensity?Homework Equations Resistors: Connection in series: same current Connection in parallel: same delta V The Attempt at a Solution A and C are in series. They'll be equally bright. B is not connected to the negative terminal of...
  34. Avijit Palit

    B How to increase brightness of projector

    I have made a smartphone projector. But is has low brightness. How to increase brightness of projector... Help please
  35. C

    Difference in Brightness between Two Bulbs

    Homework Statement Two lightbulbs of resistance R1 and R2 (R2 > R1) are connected in series. Which is brighter? What if they are connected in parallel? Explain. Homework Equations P=V^2/R P=I^2R The Attempt at a Solution I know the solution. In series, P1=I^2R1 < P2=I^2R2, so R2 is...
  36. kamhogo

    Resistors (lightbulbs) Power & Brightness

    Homework Statement A 60 W lightbulb and a 100 W lightbulb are placed one after another ( in series, the 60 W battery closer to the positive terminal of the battery) in a circuit. The battery's emf is large enough that both bulbs are glowing. Which is the true statement? A. The 60 W bulb is...
  37. NihalRi

    Stargazing Brightness of objects through a telescope

    Hi my question is about how the brightness of stellar objects is effected when we look at them through a telescope. Firstly when I looked through a telescope I noticed there were more stars I could see. Is the reason because a telescope can gather more light than our eye or does it have...
  38. A

    Surface brightness and effective radius

    Homework Statement Assuming that the average surface brightness within the effective radius is 19 mag/arcsec2, use the definition of the effective radius to estimate what the effective radius in kpc would be for NGC 4216 if it was an elliptical galaxy. Homework Equations All the logs are base...
  39. S

    Calculating Relative Brightness of Type Ia Supernovae

    Dear all, I am trying to understand the plot below: http://supernova.lbl.gov/PDFs/expansionhistoryphystoday.pdf by S.Perlmutter. However, I don't get the meaning of the "relative brightness" of SN. How is it calculated? Is the brightness of each SN compared to a special one?
  40. AstroJMT42

    Switches changing brightness of bulbs

    Homework Statement All bulbs are identical, (no information given on resistance so assuming all the same) All the switches are closed and then S1 is opened, Does bulb 6 get brighter, dimmer or stay the same? Does bulb 4 get brighter, dimmer or stay the same? Explain briefly why. Homework...
  41. M

    How Six 2V lamps could be lit to their normal brightness.

    Homework Statement [/B] Homework EquationsThe Attempt at a Solution I'm not really sure how to attempt this question tbh. In order for the lamps to have normal brightness I think the circuit must be parallel. I also think maybe for A there can only be one lamp per branch because there's...
  42. H

    Surface vs Apparent Brightness

    I'm confused what the difference between the two are...I thought surface brightness was luminosity, but apparently it's not: L=Surface brightess x Area...But I came across a similar equation that seems to assume surface brightness is the same as apparent brightness. Please help! Edit: Also, why...
  43. B

    Brightness of bulbs in series and parallel

    Homework Statement Bulbs in series are less bright than those in a parallel circuit. But are all the bulbs in the series circuit equally dim? Homework EquationsThe Attempt at a Solution I think for the purpose of high school physics bulbs in series are considered to be equally dim in a series...
  44. A

    Lamp Brightness with Varying AC: Understanding the Consistent Output

    AC is varying.So why does the brightness not vary?
  45. 2

    Stefan-Boltzmann law, luminosity, brightness and magnitude?

    From what I understand, in the equation P=\sigma AT^4, P is the power output of the star which is the energy radiated per second in EM radiation of all frequencies, and I think luminosity is also defined as the energy radiated per second in EM radiation of all frequencies. Therefore luminosity...
  46. G

    Determining the brightness on a projected surface

    I'm trying to determine how bright my projection image will be on a projected surface. I'm struggling to find a formula for this. I'm using (for example) the Canon Rialis projector which is 4500 lumens. I would be using the zoom lens with maximum zoom so the throw ratio would be 7:1. At a...
  47. J

    Prism -- brightness of a ray of white light as it passes through a prism?

    What happens to the brightness of a ray of white light as it passes through a prism?
  48. K

    The relationship between brightness of bulb and power rating

    I came across a question: Four bulbs with different power rating, bulb A (240V, 40W), bulb B (110V, 36W), bulb C (12V, 60W) and bulb D (6V, 0.5W) are connected to relevant power sources. Which bulb is the brightest. At first, i thought the highest power will be the brightest. But the answer is...
  49. P

    Lightbulb brightness in a circuit

    Homework Statement The circuit has identical light bulbs. A fourth identical light bulb is added to the circuit. How does the brightness of the original light bulbs change? a)All of them get dimmer b)X,Z get dimmer, Y brighter c)X,Z brighter, Y dimmer d)X,Y dimmer, Z brighter e)X,Y brighter, Z...